You may have noticed that I haven't posted anything in a while. That's largely due to the fact that nothing interesting has happened in a while. I'm pleased to report the Z3 continues to zip along trouble free and in relative quiet (still can't find that pesky rattle). People occasionally ask me about the car, but I haven't had any interactions that are worth mentioning lately. I've had a number of people tell me I should drive it down to the BMW dealership nearby and show it to them. I'm kind of torn on this, I can see it going one of two ways. One, they are interested and a few people come out to look at it. Or two, they don't give a damn and are irritated that I'm taking up their time and not there to buy a new car from them. I'm just not sure it's worth my time.
The batteries have been a complete non-issue. Meaning that I charge them, I discharge them, and they do nothing out of the ordinary or unexpected. I still need to bottom balance the pack, but I simply haven't had the time, what with the holidays and all. However, I have had time to think about it and draw my own conclusions on the topic.
As I see it, bottom balancing means I'm not going to run the risk of ruining one or more cells by driving them to reversal if I draw the pack down too far. So that's one argument for the case. I may not be able to charge all the cells all the way up if they have slightly different capacity, but that difference is so minimal, it has almost no impact on range; less than a mile, probably 1/2 a mile at worst. I may have to tinker with the charger to make sure it cuts off at the 3.45 volts I've been using, but so be it. Having to set the charger for the proper cut-off is necessary regardless where you balance the pack, top or bottom, or even if it's not balanced at all. So that is not a factor. If we tally that up, we have one positive and two non-issues.
If I top balance the pack, I can be sure all the batteries are fully charged at the end of a charging cycle, which gets me nothing really. I may be able to squeeze out that extra 1/2 mile I mentioned before, but there is always the ever present danger of reversing a cell or two if I discharge too far because some hit bottom first. Setting the charger for the proper cutoff still has to be done, so that's not any different from bottom balancing. So, that's one strike against top balancing, and two non-issues. If you weigh it up, you see where the balance falls (no pun intended).
I learned something about Ohm's law in September. I had no idea why turning down the current I was charging at would push the batteries to too high a voltage. To be clear, I had no idea it would happen, and after it did, no idea why! I tinkered around with the charger settings for a month before I understood what was happening, but still had no idea why. Jack Rickard was kind enough to explain it to me and mentioned that even he'd fallen victim to it. I suggested to him that if we both had been bitten, others might as well, and that he may want to mention it on one of his weekly shows. Boy did he! Fully half of one of his shows was dedicated to showing how I messed up and explaining why it happened. To me, this may be one of the best shows he's published. If we can point out the land mines involved with these batteries, hopefully people won't step on them. They really are the best solution for enthusiast, home built EVs at this time. Fortunately, the batteries are robust enough to withstand even my clumsiness. Dr. Jay Whitacre pointed out that as long as the cells are not charged above 4.3 volts, they are more or less unaffected. Mine never came close to that kind of voltage.
From the time the car rolled out of the garage until roughly two months ago, I watched the Link-10 meter like a hawk, and range anxiety was a real issue for me. I suppose that watching the meter over that time was necessary for learning purposes. But eventually what I learned is that there really isn't much reason to watch it at all. I know how far the car will go, I know how far my trips are, so range anxiety is really not part of my reality anymore. This year I've come across only a handful of instances where I needed to use my ICE car instead of the Z3. Most of those times it was because I needed to carry more than one person. One of those was because I needed to carry some 2x4's home from the hardware store (tough to do in a Z3). I can recall only one occasion where I needed the ICE because I needed to drive across town and range was an issue.
Summer was tough. It was too hot to drive the car because there was no AC. The Zilla kept flashing at me warning that it was getting too hot. I'd back off the throttle, or coast,a bit and the Zilla would stop complaining. I can fix the AC problem, but it will involve removing the batteries up front and hiring someone to come out and fabricate hoses for me. I could throw a bigger radiator at the Zilla to dissipate heat better, but I'm not too sure that would be very effective when the air is 120 °F or hotter on the street. I may try, but it may be a mute point as I'm about to explain.
My real concern is the batteries. They typically warm up to between 15° to 25° over the ambient air temperature, and that's the temperature taken at the terminals, internally it's bound to be warmer. I have no idea how much warmer, but it's probably on a few degrees. They all have plenty of airflow around them, but there is only so much cooling 120° air can do. The problem is the electrolyte in the cells starts to degrade between 135° and 140 °F. It's easy to see how that temperature can be achieved in the Arizona summer if the batteries run 25° hotter than the ambient air. Keep in mind that when you hear that it's 110° in Phoenix, that's at the airport. If you actually measure the temperature of the air over any surface street in the valley, it's going to be North of 118 °F. Heat is the second biggest threat to these batteries, and unfortunately summertime in Phoenix has that in spades. I may very well end up using the car only 9 months out of the year, which is too bad.
There you have it; the good and the bad, the ups and the downs. Nothing really earth shattering on either side of the spectrum, and I suppose that's good. I was shooting for a car that I could just charge and drive, relatively worry free, and that's pretty much what I got, now that everything has settled down from the motor problems in May and the charging problems in September. I've put over 3150 miles on the car. It has become my daily driver. It's rare that I have to drive my ICE car. I've said this many, many times before and I think that manufacturers need to use this logic when selling EVs, If you have more than one car, the chances are very good that one of them could be an EV and you wouldn't notice a difference in your life except that it would save you money in the long run. If you have more than 2 cars, then it's an almost certainty that one of them could be an EV and you'd never feel any inconvenience apart from a heavier wallet.
When we get to March 2nd, the anniversary of the Z3's road debut, I'll publish every sordid detail and piece of information I can find on the car. I've been keeping tabs on quite a lot of data, and I'll share it all then. In the mean time have a wonderful new year, and thanks for reading!
Friday, December 31, 2010
Friday, December 3, 2010
Test Driving a Leaf
Today was the day I had signed up to test drive the Nissan Leaf. Every year around this time, the city of Tempe has a street fair with artists and artisans displaying their wares for Christmas shoppers. Nissan set their tents up in and advantageous spot adjacent to the fair, sure to get a lot of traffic.
Once I arrived and was checked in, I had to wait about 15 minutes before the next group of people were taken on the tour. I, and all the others were walked through three different tents each designed to educate you on a specific aspect of the Leaf.
First was the technology tent. They explained the Leaf has a 24 kWh pack that weighs 600 lbs, and a lot of other information that is readily available on the web. What I did learn was that the engineers at Nissan have designed the software to allow you to draw down to a 95% depth of discharge (vs. the Volt's 50%). That's pretty gutsy and must mean they are very confident in the battery pack. The pack is composed of 48 Lithium Ion manganese cells. Apparently it's the manganese that tames these cells and prevents them from spontaneously combusting like standard lap top batteries can do. I was also surprised to learn that the battery pack is cooled only by the natural flow of air through the compartment. No fans, no liquid, just wind generated by moving forward, directed into the pack. They said they'd tested it in Tucson during the summer and the batteries were fine. Not unlike what I've found with my LiFePo4 cells.
The second tent was more about sales and painting customer expectations. They touted the cost advantages of driving the car, specifically of electric vs. gas, and they showed off the iPhone app that you can use to keep track of the car. The app is pretty slick. It will tell you all the current status, and even alert you if someone unplugs your car. You can also start the AC system from anywhere; a feature people in Arizona and other hot states will find particularly appealing. While they didn't mention it, I'm sure the same applies to the heating system for colder climates.
The last tent was simply to talk about range and deal with range anxiety. The Leaf comes with Sat-Nav standard and it will paint on the screen circles radiating from your position, that indicate how far you can go. Nifty.
Then it was out to look at the car and drive it. They had the hood open on one and I saw what looked like a valve cover with the Nissan logo. It was actually the top of the inverter, but they said the designed it to look like a valve cover so people would feel more familiar with it.
I met my Nissan co-driver, a pretty young girl named Alex. This was her first day and she knew nothing about the car. Easy enough, it meant I could save my questions for later. I got to drive the Leaf for a grand total of... .3 miles. That's right, around the block. It was slow traffic, but I did get to experience it. I was surprised that when I took my foot off the brake, the car started creeping forward, just like an automatic. Again, Nissan trying to mimic what you're used to and make you comfortable. I never got the car over 25, so I have no idea how it handled at speed. Hell, I never took a corner faster than 5 MPH. I did gun it from a stop at one corner and I was impressed. Just what you'd expect, plenty quick. A tad faster than the Z3.
The brakes took some getting used to. A little pressure and you were slowing down, a little more and you jerked to a stop. I don't quite know how they have the regenerative braking set up, but the scale of pressure applied to the pedal to the amount of regen was not as linear as I would have thought. Over all, the car was remarkable in just how ordinary it was. It's clear that's what Nissan is shooting for. All the benefits of a fully electric car, without scaring people with anything unfamiliar.
Had I not went ahead and built my own, I'd be very tempted to buy a Leaf. For people who want an EV but don't want to build their own, then I'd say go for it. It's just too bad that while the engineers were so hard at work designing the car to be so good and feel "normal" that they couldn't have designed out some of the ugly.
Once I arrived and was checked in, I had to wait about 15 minutes before the next group of people were taken on the tour. I, and all the others were walked through three different tents each designed to educate you on a specific aspect of the Leaf.
First was the technology tent. They explained the Leaf has a 24 kWh pack that weighs 600 lbs, and a lot of other information that is readily available on the web. What I did learn was that the engineers at Nissan have designed the software to allow you to draw down to a 95% depth of discharge (vs. the Volt's 50%). That's pretty gutsy and must mean they are very confident in the battery pack. The pack is composed of 48 Lithium Ion manganese cells. Apparently it's the manganese that tames these cells and prevents them from spontaneously combusting like standard lap top batteries can do. I was also surprised to learn that the battery pack is cooled only by the natural flow of air through the compartment. No fans, no liquid, just wind generated by moving forward, directed into the pack. They said they'd tested it in Tucson during the summer and the batteries were fine. Not unlike what I've found with my LiFePo4 cells.
The second tent was more about sales and painting customer expectations. They touted the cost advantages of driving the car, specifically of electric vs. gas, and they showed off the iPhone app that you can use to keep track of the car. The app is pretty slick. It will tell you all the current status, and even alert you if someone unplugs your car. You can also start the AC system from anywhere; a feature people in Arizona and other hot states will find particularly appealing. While they didn't mention it, I'm sure the same applies to the heating system for colder climates.
The last tent was simply to talk about range and deal with range anxiety. The Leaf comes with Sat-Nav standard and it will paint on the screen circles radiating from your position, that indicate how far you can go. Nifty.
Then it was out to look at the car and drive it. They had the hood open on one and I saw what looked like a valve cover with the Nissan logo. It was actually the top of the inverter, but they said the designed it to look like a valve cover so people would feel more familiar with it.
I met my Nissan co-driver, a pretty young girl named Alex. This was her first day and she knew nothing about the car. Easy enough, it meant I could save my questions for later. I got to drive the Leaf for a grand total of... .3 miles. That's right, around the block. It was slow traffic, but I did get to experience it. I was surprised that when I took my foot off the brake, the car started creeping forward, just like an automatic. Again, Nissan trying to mimic what you're used to and make you comfortable. I never got the car over 25, so I have no idea how it handled at speed. Hell, I never took a corner faster than 5 MPH. I did gun it from a stop at one corner and I was impressed. Just what you'd expect, plenty quick. A tad faster than the Z3.
The brakes took some getting used to. A little pressure and you were slowing down, a little more and you jerked to a stop. I don't quite know how they have the regenerative braking set up, but the scale of pressure applied to the pedal to the amount of regen was not as linear as I would have thought. Over all, the car was remarkable in just how ordinary it was. It's clear that's what Nissan is shooting for. All the benefits of a fully electric car, without scaring people with anything unfamiliar.
Had I not went ahead and built my own, I'd be very tempted to buy a Leaf. For people who want an EV but don't want to build their own, then I'd say go for it. It's just too bad that while the engineers were so hard at work designing the car to be so good and feel "normal" that they couldn't have designed out some of the ugly.
Thursday, December 2, 2010
A Good Drive
Earlier in the week I made plans to go see a friend of mine who lives about 25 miles away in Maricopa. I had planned on taking my gas car, but when my daughter absconded with it, I was left with the Z3. Now, a 50 mile trip shouldn't be a problem for the car, after all it's full range is closer to 60 miles. But this would be the longest trip I've clocked up and most of it would be at freeway speeds. I asked my friend if I could charge up a bit when I arrived and he graciously agreed.
The ride down was pretty uneventful, and I averaged just over 55 mph. At that rate, I watched about 2 amp/hours per mile (320 Watt/hours) click off the Link 10. By the time I arrived, I'd used 52.1 amp/hours for a total of 8.34 kW/hours of the 19.2 available. Some of you may remember that I've got 120 amp/hour CALB cells.
As I rolled into the driveway, the trip meter clicked to 25 miles, we ran the extension cord out and I gratefully plugged in. I set the charger so that it would pull no more than 10 amps. I watched for a minute, no breakers tripped and all was good.
When I went to leave, I saw the charger was off; uh oh. While the breaker never tripped, the power strip that he'd plugged into was not happy with the current and it tripped. I'd managed to pack in 1 full amp/hour before it tripped. Should have checked it. So, with 51.1 amp hours down on the pack I headed for home. "Should be no problem, I've got up to 120 to use," I thought.
Apparently Maricopa is slightly down hill from my house, which now meant I was going back up the hill to Phoenix. I watched as just over 2 amp/hours per mile clicked off the Link 10. I was 95% confident that there would be no problems. I guess you could call that 5% range anxiety (something I gave up on as silly some time ago). For the record, traveling at 55 MPH in 4th gear, the motor turned at about 2800 RPM, and it drew between 2.0 and 2.1 amp/hours per mile, or between 320 and 336 Watt/hours per mile if you prefer.
By the time I rolled up into my driveway, I'd drawn a total of 106.5 amp/hours off the pack. This marked the first time I drew the batteries down below 80% depth of discharge, 88.8% to be precise. There was absolutely no noticeable difference in the way the car drove from when I pulled out of my driveway, apart for the Link 10 blinking at me incessantly that I'd used too much current.
I was curious to see how the batteries measured up after that drive, so I left them to rest for 15 minutes and then took a reading off each cell. The highest cell was at 3.248V, and apart from one cell, the lowest as at 3.231V, but 80% of the cells were at 3.241 + or - 0.003V. The entire pack was at 155.7V vs. 160.0V when it's fully charged.
There was one cell at 3.221V. If I weren't careful, and I ran the pack down too far, that cell is likely the first that would die a horrible death. I'm seeing more and more why bottom balancing the cells is a better strategy than following no strategy, and way better than top balancing. If you're watching amp/hours in and out, not over charging is a snap. But if you're interested in drawing the pack down beyond 80%, you'd be better off making sure all the cells hit bottom at the same time. I need to re-watch some of Mr. Rickard's videos to get details on how to do it.
All in all, it was a great learning experience and I was terrifically impressed with how well the car did. These batteries really are amazing.
The ride down was pretty uneventful, and I averaged just over 55 mph. At that rate, I watched about 2 amp/hours per mile (320 Watt/hours) click off the Link 10. By the time I arrived, I'd used 52.1 amp/hours for a total of 8.34 kW/hours of the 19.2 available. Some of you may remember that I've got 120 amp/hour CALB cells.
As I rolled into the driveway, the trip meter clicked to 25 miles, we ran the extension cord out and I gratefully plugged in. I set the charger so that it would pull no more than 10 amps. I watched for a minute, no breakers tripped and all was good.
When I went to leave, I saw the charger was off; uh oh. While the breaker never tripped, the power strip that he'd plugged into was not happy with the current and it tripped. I'd managed to pack in 1 full amp/hour before it tripped. Should have checked it. So, with 51.1 amp hours down on the pack I headed for home. "Should be no problem, I've got up to 120 to use," I thought.
Apparently Maricopa is slightly down hill from my house, which now meant I was going back up the hill to Phoenix. I watched as just over 2 amp/hours per mile clicked off the Link 10. I was 95% confident that there would be no problems. I guess you could call that 5% range anxiety (something I gave up on as silly some time ago). For the record, traveling at 55 MPH in 4th gear, the motor turned at about 2800 RPM, and it drew between 2.0 and 2.1 amp/hours per mile, or between 320 and 336 Watt/hours per mile if you prefer.
By the time I rolled up into my driveway, I'd drawn a total of 106.5 amp/hours off the pack. This marked the first time I drew the batteries down below 80% depth of discharge, 88.8% to be precise. There was absolutely no noticeable difference in the way the car drove from when I pulled out of my driveway, apart for the Link 10 blinking at me incessantly that I'd used too much current.
I was curious to see how the batteries measured up after that drive, so I left them to rest for 15 minutes and then took a reading off each cell. The highest cell was at 3.248V, and apart from one cell, the lowest as at 3.231V, but 80% of the cells were at 3.241 + or - 0.003V. The entire pack was at 155.7V vs. 160.0V when it's fully charged.
There was one cell at 3.221V. If I weren't careful, and I ran the pack down too far, that cell is likely the first that would die a horrible death. I'm seeing more and more why bottom balancing the cells is a better strategy than following no strategy, and way better than top balancing. If you're watching amp/hours in and out, not over charging is a snap. But if you're interested in drawing the pack down beyond 80%, you'd be better off making sure all the cells hit bottom at the same time. I need to re-watch some of Mr. Rickard's videos to get details on how to do it.
All in all, it was a great learning experience and I was terrifically impressed with how well the car did. These batteries really are amazing.
Tuesday, November 30, 2010
A Visitor
Since I finished the car, I've had a number of people either visit me at my house, or who I've met up with. Each visit has been a lot of fun and I've written about most. Last week, a man from Tucson named Wes stopped by to see the car. We'd been trying to schedule a time to meet for a couple months and our schedules just didn't quite work out. But as it happened, we both had time the day before Thanksgiving.
Wes rolled up in Ford Ranger. He'd purchased the truck a few months back with the intent of converting it to an EV. Who can blame him, it's a good choice. Then he happened across the EV Z3 on the web and thought it was a great idea. He's now reconsidering the Ranger in favor of a Z3. The ranger has a lot of advantages over the Z3: more room for batteries, it can carry more weight, parts are likely cheaper and it has way more room to work with when locating and installing components. But you have to admit, a Z3 is a tad sexier, and I can attest that its way more fun to drive.
Wes and I stood around the car for an hour or so talking about different elements of the construction. He had a lot of good questions and I could see his mind spinning as he was filing it all away. We went out for a ride, and took it on the freeway near my house. Of course the car did just fine, and Wes had an opportunity to see just how fun riding in an EV is. We got back and I shot this picture of Wes next to the car.
I needed a bigger flash. I don't know if Wes will sell the Ranger and pick up a Z3 to do the conversion, but I hope he does. If he does, I hope he figures out better ways to solve some of the problems I encountered. I offered to share anything I'd learned with him, but I think it would be fantastic if he builds one that puts mine to shame. Leave a comment with some encouragement for Wes. How great would it be to have two EV Z3s on the road in Arizona?! Thanks for stopping by Wes.
Wes rolled up in Ford Ranger. He'd purchased the truck a few months back with the intent of converting it to an EV. Who can blame him, it's a good choice. Then he happened across the EV Z3 on the web and thought it was a great idea. He's now reconsidering the Ranger in favor of a Z3. The ranger has a lot of advantages over the Z3: more room for batteries, it can carry more weight, parts are likely cheaper and it has way more room to work with when locating and installing components. But you have to admit, a Z3 is a tad sexier, and I can attest that its way more fun to drive.
Wes and I stood around the car for an hour or so talking about different elements of the construction. He had a lot of good questions and I could see his mind spinning as he was filing it all away. We went out for a ride, and took it on the freeway near my house. Of course the car did just fine, and Wes had an opportunity to see just how fun riding in an EV is. We got back and I shot this picture of Wes next to the car.
Thursday, November 18, 2010
The Leaf
Today was the first day I've seen a Nissan Leaf on the road. I was cruising along in the EV Z3 when I saw it approach from the other direction. I recognized it as a Leaf right away, but had second thoughts because I didn't think they'd be available for sale just yet. I figured it must be a Versa, which is the same platform.
But it had that unmistakable trapezoidal door on the front bumper where the charging receptacles are hidden. As it passed I looked back and it had new car plates on it. Sure enough, it was a Leaf. I thought how cools is that, two electric cars passing each other on the busy streets of Phoenix. Of course the driver of the Leaf had no idea there was another electric car anywhere nearby.
I've actually signed up to go test drive a Leaf on December 3rd. I'm really looking forward to it. I'm eager to see how they packaged the whole thing and how well it drives. I'm sure it will be just fine. I really do hope Nissan sells a bunch of these cars. I really hope that every other manufacturer sells thousands of the EVs they're each planning for the future. It's going to be fun to ask the salesman about the car. I hope they have someone there who really knows what he or she is talking about and can give me real data on the car. We shall see. I have no intention of buying one at this time. After all I already own an EV.
As I drove past the Leaf, I couldn't help think to compare the only two EVs in what was very likely a several mile radius. The Leaf was designed from the ground up as an EV and was built by professionals. It's likely to be relatively free of problems and will come with a sweet warranty. It will travel around 100 miles per charge and has A/C.
By comparison, the Z3 was stuck together by some hack in a garage. It has no warranty, and can only go 60 miles on a charge. Plus it currently has no A/C, and won't until that same hack gets off his butt and does something about it. But I ask you. Which one would you rather drive? I knew unequivocally what my answer was as I drove by.
But it had that unmistakable trapezoidal door on the front bumper where the charging receptacles are hidden. As it passed I looked back and it had new car plates on it. Sure enough, it was a Leaf. I thought how cools is that, two electric cars passing each other on the busy streets of Phoenix. Of course the driver of the Leaf had no idea there was another electric car anywhere nearby.
I've actually signed up to go test drive a Leaf on December 3rd. I'm really looking forward to it. I'm eager to see how they packaged the whole thing and how well it drives. I'm sure it will be just fine. I really do hope Nissan sells a bunch of these cars. I really hope that every other manufacturer sells thousands of the EVs they're each planning for the future. It's going to be fun to ask the salesman about the car. I hope they have someone there who really knows what he or she is talking about and can give me real data on the car. We shall see. I have no intention of buying one at this time. After all I already own an EV.
As I drove past the Leaf, I couldn't help think to compare the only two EVs in what was very likely a several mile radius. The Leaf was designed from the ground up as an EV and was built by professionals. It's likely to be relatively free of problems and will come with a sweet warranty. It will travel around 100 miles per charge and has A/C.
By comparison, the Z3 was stuck together by some hack in a garage. It has no warranty, and can only go 60 miles on a charge. Plus it currently has no A/C, and won't until that same hack gets off his butt and does something about it. But I ask you. Which one would you rather drive? I knew unequivocally what my answer was as I drove by.
Saturday, November 13, 2010
An Interested Individual
Yesterday, as I was leaving the grocery store, a man walked up to me and asked if the Z3 was a conversion. I told him it was, and he asked if it was a hybrid. I said that no, it was an full electric car, to which he said "Really!?"
What initially caught his eye is that he has a Z3 that is also Helrot (bright red in German) and he noticed the Alternative Fuel plate. He said his first thought was that it was a propane/gas dual fuel vehicle. There are quite a few of those here in AZ (mostly SUVs) due to a botched program sponsored by our state legislature which nearly bankrupted the state. But then he realized it probably wasn't, as there would be no room for a propane tank. Once I told him it was electric, he started asking a lot of great questions.
He asked if he could peek under the hood and I happily opened the car up. He said that he'd had no idea BMW was making electric Z3s. I explained that they weren't, I had made it. He was surprised, as most people are and continued to ask more insightful questions. Every time this happens I like to let that idea sort of sink in; the idea that it was built by just one guy. I really want people to consider the possibility that they too could take on such a project.
I explained how the motor was coupled to the original transmission, a little about the batteries, their capacity and their life expectancy, the cost of the conversion, how far I can drive it and how long it takes to charge. It turns out that he worked in the aircraft industry, and he recognized and appreciated some of the safety designs that I'd incorporated into the car.
When we parted ways, we were both smiling, having enjoyed such a great chance encounter. I understand why a lot of people that convert cars put stickers and labels on the car proclaiming that it's an electric car. It's great to have people ask about it. I love it when people ask about it! But all those stickers and banners aren't for me. I like the clean look of the unadulterated car. I think as more people hear the term "EV" the custom license plate on the car will get a bit more attention. And to that gentleman that stopped me in the parking lot, thanks for asking about the car. I really enjoyed chatting with you.
What initially caught his eye is that he has a Z3 that is also Helrot (bright red in German) and he noticed the Alternative Fuel plate. He said his first thought was that it was a propane/gas dual fuel vehicle. There are quite a few of those here in AZ (mostly SUVs) due to a botched program sponsored by our state legislature which nearly bankrupted the state. But then he realized it probably wasn't, as there would be no room for a propane tank. Once I told him it was electric, he started asking a lot of great questions.
He asked if he could peek under the hood and I happily opened the car up. He said that he'd had no idea BMW was making electric Z3s. I explained that they weren't, I had made it. He was surprised, as most people are and continued to ask more insightful questions. Every time this happens I like to let that idea sort of sink in; the idea that it was built by just one guy. I really want people to consider the possibility that they too could take on such a project.
I explained how the motor was coupled to the original transmission, a little about the batteries, their capacity and their life expectancy, the cost of the conversion, how far I can drive it and how long it takes to charge. It turns out that he worked in the aircraft industry, and he recognized and appreciated some of the safety designs that I'd incorporated into the car.
When we parted ways, we were both smiling, having enjoyed such a great chance encounter. I understand why a lot of people that convert cars put stickers and labels on the car proclaiming that it's an electric car. It's great to have people ask about it. I love it when people ask about it! But all those stickers and banners aren't for me. I like the clean look of the unadulterated car. I think as more people hear the term "EV" the custom license plate on the car will get a bit more attention. And to that gentleman that stopped me in the parking lot, thanks for asking about the car. I really enjoyed chatting with you.
Wednesday, November 3, 2010
Car Show Number 2
Today was the second car show in as many days. Unfortunately, the heat has decided to hang around a bit long here in Phoenix, so while the rest of the country is enjoying the crisp fall weather, it was 92° F and sunny. Too sunny, if you ask me.
Any way, one of our local power companies, SRP, was putting on what they call the "Party for the Planet" event. Apparently this is a yearly event for SRP. They have multiple booths with a wide variety of different groups showcasing their green technologies or methods. One addition they thought would be good was to throw in a few electric cars, so they asked me if would be willing to bring the EV Z3 down. It was a nice turn out of mostly SRP employees.
As it turned out, there were three EVs present. Take a look:
Up front, you can see a Citicar owned by one of the EAA local members named Bruce. Behind that is a Ford Probe owned by SRP employee Abel. Abel told me that the car had originally been owned by SRP and used for electric racing. They sold it away, and he ended up getting some time later from the second owner. It's an AC drive system using Optima yellow top lead acid cells. Eventually Abel wants to drop some lithium cells in it. Behind his car, just peeking around the corner is the little Z3.
Quite a few people stopped by to take a look at it and ask questions.
It was the usual battery of questions, which is just fine. A few people had some insightful questions which is always fun to come across. The nice thing about this show is that there were way more pretty girls stopping by telling me how cute the car was. One girl took some pictures and asked lots of questions that she then forwarded off to her boyfriend who is a BMW enthusiast. I have to tell you, I wonder how BMW enthusiasts would react to this car. I'm not sure if they'd find it really cool, or want to stone me on the spot for perpetrating such sacrilege. She encouraged me to take the car to a dealership thinking that BMW corporate would be very interested in hearing about the car. Perhaps they would. My thought is that it would largely be a waste of time.
At any rate, it was a great day showing off the car, opening peoples minds to the potential of converting a car themselves. It was just too damned hot.
Any way, one of our local power companies, SRP, was putting on what they call the "Party for the Planet" event. Apparently this is a yearly event for SRP. They have multiple booths with a wide variety of different groups showcasing their green technologies or methods. One addition they thought would be good was to throw in a few electric cars, so they asked me if would be willing to bring the EV Z3 down. It was a nice turn out of mostly SRP employees.
As it turned out, there were three EVs present. Take a look:
Quite a few people stopped by to take a look at it and ask questions.
At any rate, it was a great day showing off the car, opening peoples minds to the potential of converting a car themselves. It was just too damned hot.
Tuesday, November 2, 2010
Car Show Number 1
Just over a month ago, I was able to attend one of the monthly meetings of the Electric Automobile Association hosted by the Phoenix Chapter. It was entertaining and I had the opportunity to meet a few interesting people. One of the people I met was a gentleman named Jim who has been interested in converting a car for some time, and he asked me if I'd be willing to come show the car to him and some of his friends at work. I told him that I'd be happy to do so.
Well, as luck would have it, the company he works for, General Dynamics, decided to put on a car show for it's employees. He invited me to attend that instead, and I agreed, thinking it would be a great way to get the car seen and hopefully inspire a few people. I think all the cars there were actually owned by employees, with one exception; mine.
It started off yesterday with a request to feature the Z3 and one other guy's car in a press release meant to garner some publicity for the event. I consented and gave them a little information about the car. Today, as I pulled up to the check in desk, they knew me right away. I guess word had gotten around, and they all seemed genuinely grateful that I brought the car out. They told me I was going to be parked along side all the "showcase" cars.
I pulled around and parked next to a couple of Cobras, and a slew of 60 muscle cars. I found the whole thing a bit incongruous. Here are all these loud, big, beautiful muscle cars, and then there, in amongst them, almost lost, was my little Z3. I began to wonder how much interest it would garner.
Well, it didn't take long to find out. Before long there was a crowd gathering around the car and people asking the usual questions you'd expect. "How far can you go? How long to charge it? Did you build it yourself? How long did it take you?" Through most of the event there were at least 6 people gathered around smiling, and asking questions. Everyone seemed to have the same opinion; they all thought it was cool.
I confess, I'm not a big muscle car fan. Don't get me wrong, I'm not a green car snob. I love nice powerful, well engineered cars, but I tend to prefer European models. If I could afford it, I'd have an Aston Martin Vantage in one of my garage bays, and a Tesla right next to it. But as the day went on, I noticed something interesting. People stopped to look at the Cobras, the Cudas, the Camaros and the Vettes, but they didn't stay long. Generally there was one or two people around any given car. The little car, that seemed so out of place in the group, oddly enough was the one that drew and kept most of the attention.
It was about 10 minutes after I arrived that I reached into my pocket to get my camera when I realized that I'd left it sitting on my kitchen table. DOH! I desperately wanted to take pictures of the event and of some of the people gathered around the car, but it wasn't to be.
The good thing is that I have another chance tomorrow, at a different car show. One of our local power companies, SRP, is putting on a festival called "Party for the Planet," and they've invited me. I'll be taking the car there tomorrow, answering the same questions I did today, and hopefully remembering to take the camera so I can take a few pictures to share with you.
Well, as luck would have it, the company he works for, General Dynamics, decided to put on a car show for it's employees. He invited me to attend that instead, and I agreed, thinking it would be a great way to get the car seen and hopefully inspire a few people. I think all the cars there were actually owned by employees, with one exception; mine.
It started off yesterday with a request to feature the Z3 and one other guy's car in a press release meant to garner some publicity for the event. I consented and gave them a little information about the car. Today, as I pulled up to the check in desk, they knew me right away. I guess word had gotten around, and they all seemed genuinely grateful that I brought the car out. They told me I was going to be parked along side all the "showcase" cars.
I pulled around and parked next to a couple of Cobras, and a slew of 60 muscle cars. I found the whole thing a bit incongruous. Here are all these loud, big, beautiful muscle cars, and then there, in amongst them, almost lost, was my little Z3. I began to wonder how much interest it would garner.
Well, it didn't take long to find out. Before long there was a crowd gathering around the car and people asking the usual questions you'd expect. "How far can you go? How long to charge it? Did you build it yourself? How long did it take you?" Through most of the event there were at least 6 people gathered around smiling, and asking questions. Everyone seemed to have the same opinion; they all thought it was cool.
I confess, I'm not a big muscle car fan. Don't get me wrong, I'm not a green car snob. I love nice powerful, well engineered cars, but I tend to prefer European models. If I could afford it, I'd have an Aston Martin Vantage in one of my garage bays, and a Tesla right next to it. But as the day went on, I noticed something interesting. People stopped to look at the Cobras, the Cudas, the Camaros and the Vettes, but they didn't stay long. Generally there was one or two people around any given car. The little car, that seemed so out of place in the group, oddly enough was the one that drew and kept most of the attention.
It was about 10 minutes after I arrived that I reached into my pocket to get my camera when I realized that I'd left it sitting on my kitchen table. DOH! I desperately wanted to take pictures of the event and of some of the people gathered around the car, but it wasn't to be.
The good thing is that I have another chance tomorrow, at a different car show. One of our local power companies, SRP, is putting on a festival called "Party for the Planet," and they've invited me. I'll be taking the car there tomorrow, answering the same questions I did today, and hopefully remembering to take the camera so I can take a few pictures to share with you.
Saturday, October 30, 2010
Back to a Routine
With the last couple month's posts dedicated to various issues surrounding charging and the batteries, I'm happy to report things have become boring again.
I've already written about the two mistakes I made through this whole thing, hoping that others can learn from my mistakes. First, if you have a charger with the capacity to adjust the current it pushes to the batteries, don't expect that adjusting it up or down will have no influence on the total amount of energy that is ultimately pushed to the pack. Second, a misguided attempt to balance the batteries has done nothing good. In fact it's forced me to sacrifice a small portion of the top of the pack and likely made the bottom more perilous (but I don't intend to find that out).
My goal since all of this began was to find the correct cutoff voltage for the charger. It was a long process, trying different voltages, watching the batteries closely each time. To be honest, it sucked. But during the whole endeavor, I never allowed any of the cells to pass the 3.6 volt cell limit. Ultimately what I found was setting the chargers cutoff voltage for 164.4 volts, at a current of 20 amps seems to do the trick nicely.
The goal has been to charge the pack so that no cell exceeds 3.45 volts. You may recall that originally I was charging to 3.5 volts, but when attempting that now, I found that some cells would occasionally try to head North of 3.6 with a few minutes left on the charger's timer. So, 3.45 seems to be the order of the day.
I've charged the pack some 35 times now and in every case it has gone perfectly. The highest I've seen any cell go was 3.46, and that happened once. Close enough. The difference in capacity seems to be a whopping 1.3 amp/hours, which equates to 3/5's of a mile. I'll just trim off two or three quick launches from stop lights and call it even.
I'll continue monitoring them closely for some time, just to be sure nothing strange happens, and I'll report it if it does. For now though, we're back to a boring, predictable routine of charge, discharge. And I'm quite happy with that.
I've already written about the two mistakes I made through this whole thing, hoping that others can learn from my mistakes. First, if you have a charger with the capacity to adjust the current it pushes to the batteries, don't expect that adjusting it up or down will have no influence on the total amount of energy that is ultimately pushed to the pack. Second, a misguided attempt to balance the batteries has done nothing good. In fact it's forced me to sacrifice a small portion of the top of the pack and likely made the bottom more perilous (but I don't intend to find that out).
My goal since all of this began was to find the correct cutoff voltage for the charger. It was a long process, trying different voltages, watching the batteries closely each time. To be honest, it sucked. But during the whole endeavor, I never allowed any of the cells to pass the 3.6 volt cell limit. Ultimately what I found was setting the chargers cutoff voltage for 164.4 volts, at a current of 20 amps seems to do the trick nicely.
The goal has been to charge the pack so that no cell exceeds 3.45 volts. You may recall that originally I was charging to 3.5 volts, but when attempting that now, I found that some cells would occasionally try to head North of 3.6 with a few minutes left on the charger's timer. So, 3.45 seems to be the order of the day.
I've charged the pack some 35 times now and in every case it has gone perfectly. The highest I've seen any cell go was 3.46, and that happened once. Close enough. The difference in capacity seems to be a whopping 1.3 amp/hours, which equates to 3/5's of a mile. I'll just trim off two or three quick launches from stop lights and call it even.
I'll continue monitoring them closely for some time, just to be sure nothing strange happens, and I'll report it if it does. For now though, we're back to a boring, predictable routine of charge, discharge. And I'm quite happy with that.
Thursday, October 21, 2010
Charging Mystery Solved
Well at least I think it's solved. The mystery I'm referring to is why did some of the batteries suddenly start accepting more charge than they should have? My first assumption was that they'd moved in their state of charge relative to the others. But really I had no reason to believe that other than I couldn't think of any other reason.
It was then suggested to me that perhaps those particular cells simply have a lower capacity than the others so they reached their full state of charge first. I think that's likely the case, but truthfully it could be a combination of both reasons for all I know. But that really doesn't answer the fundamental question as to why, when they'd been behaving in a very predictable way for 5 months, did they suddenly start showing the tendency to run away?
Well I think I figured it out today, and I'll explain, but I need to give you some background first. I'd mentioned before that the Manzanita Micro charger has a little potentiometer screw that you use to set the cut off voltage for charging. When the pack reaches that voltage, it switches from constant current to constant voltage and starts ramping down the current according to a timer you set. I'd also mentioned that it can be a finicky thing to set.
Some time at the beginning of August, I was charging the car and I happened to stay in the garage for a while. Normally I charge it at night during off peak hours and I just let it finish on it's own. Well this time I hung around, cleaning up a bit and I saw the charger start flashing, warning that it was overheating. When I set the charger up last February, it was nice and cool in the garage. Not so much in August. To make a long story short, I realized I didn't want to shorten the life of the charger by overheating it every time I charged up, so I decided to turn down the current a bit. Turned up all the way and it sends 28 amps to the batteries. I decided I'd turn it down to 15. Problem solved.
Well, little did I know that I'd just introduced different problem. Apparently the point at which the charger changes from constant current to constant voltage is also dependent on the current out. I now have it set to start it's ramp down when the charger reaches 164.7 volts. But that was set when I was pushing 15 amps. Today was a beautiful cool day, so I decided to give it the full 28 amps and low and behold, the charger switched to constant voltage when the pack hit 163.4 volts, leaving the pack about 3.2 kWh's short of it's full capacity. I stood there for a second thinking "what the hell?"
I started experimenting with different charging schemes and trips around the neighborhood to draw some power from the pack. I left the potentiometer screw alone and just tried different charging currents and I found a curve. Send the batteries less current and the cutoff voltage is higher. Send it higher current and the cutoff voltage dropped. Here's what it looked like:
15 amps = 164.7 cutoff
20 amps = 164.4 cutoff
25 amps = 163.9 cutoff
28 amps = 163.4 cutoff
So back in August I simply dropped the current I was pushing through the charger to keep it from over heating, and the result was that the cut off voltage I had so carefully tuned for 28 amps went up. Suddenly it was too high and ultimately ended up pushing more current to the pack than it should have. I don't know the exact date this happened, so I don't know exactly how many times it happened. I think it's more than 3 but less than 7 times.
But there's a lesson to be learned here. Don't change any thing, be it a setting or a process, and expect everything else to remain the same. Always check and double check when making a change to a procedure or setting. Also, for any of you that have a Manzanita charger, or are thinking of getting one, remember this potential issue. Don't get caught by it. I don't consider this to be a major flaw in the charger, it's minor at worst. But forewarned is forearmed.
It was then suggested to me that perhaps those particular cells simply have a lower capacity than the others so they reached their full state of charge first. I think that's likely the case, but truthfully it could be a combination of both reasons for all I know. But that really doesn't answer the fundamental question as to why, when they'd been behaving in a very predictable way for 5 months, did they suddenly start showing the tendency to run away?
Well I think I figured it out today, and I'll explain, but I need to give you some background first. I'd mentioned before that the Manzanita Micro charger has a little potentiometer screw that you use to set the cut off voltage for charging. When the pack reaches that voltage, it switches from constant current to constant voltage and starts ramping down the current according to a timer you set. I'd also mentioned that it can be a finicky thing to set.
Some time at the beginning of August, I was charging the car and I happened to stay in the garage for a while. Normally I charge it at night during off peak hours and I just let it finish on it's own. Well this time I hung around, cleaning up a bit and I saw the charger start flashing, warning that it was overheating. When I set the charger up last February, it was nice and cool in the garage. Not so much in August. To make a long story short, I realized I didn't want to shorten the life of the charger by overheating it every time I charged up, so I decided to turn down the current a bit. Turned up all the way and it sends 28 amps to the batteries. I decided I'd turn it down to 15. Problem solved.
Well, little did I know that I'd just introduced different problem. Apparently the point at which the charger changes from constant current to constant voltage is also dependent on the current out. I now have it set to start it's ramp down when the charger reaches 164.7 volts. But that was set when I was pushing 15 amps. Today was a beautiful cool day, so I decided to give it the full 28 amps and low and behold, the charger switched to constant voltage when the pack hit 163.4 volts, leaving the pack about 3.2 kWh's short of it's full capacity. I stood there for a second thinking "what the hell?"
I started experimenting with different charging schemes and trips around the neighborhood to draw some power from the pack. I left the potentiometer screw alone and just tried different charging currents and I found a curve. Send the batteries less current and the cutoff voltage is higher. Send it higher current and the cutoff voltage dropped. Here's what it looked like:
15 amps = 164.7 cutoff
20 amps = 164.4 cutoff
25 amps = 163.9 cutoff
28 amps = 163.4 cutoff
So back in August I simply dropped the current I was pushing through the charger to keep it from over heating, and the result was that the cut off voltage I had so carefully tuned for 28 amps went up. Suddenly it was too high and ultimately ended up pushing more current to the pack than it should have. I don't know the exact date this happened, so I don't know exactly how many times it happened. I think it's more than 3 but less than 7 times.
But there's a lesson to be learned here. Don't change any thing, be it a setting or a process, and expect everything else to remain the same. Always check and double check when making a change to a procedure or setting. Also, for any of you that have a Manzanita charger, or are thinking of getting one, remember this potential issue. Don't get caught by it. I don't consider this to be a major flaw in the charger, it's minor at worst. But forewarned is forearmed.
Wednesday, October 13, 2010
On Battery Balancing and Charging
As I've mentioned in the past, I'm not an expert. On anything. But in the time I've been operating the car and charging it, I've noticed a few things about these LiFePo4 batteries that I think is worth sharing. In addition, think you can draw some simple conclusions from these experiences.
You may remember that just over a month ago I noticed that a few of the batteries were hitting their max voltage before the others. The question became, did those cells move in their state of charge relative to the others, or do the simply have a slightly lower capacity. My assumption right away was that they'd drifted. Quite frankly, it never occurred to me that they might just have a lower capacity, which meant I immediately thought they'd moved relative to the other cells. Of course the first thing I thought to do to fix that was balance them to the others. I drew energy out of the all cells until every cell matched, down to 1/100 of a volt. I drove the car a few miles and then charged up.
That proved to be a complete waste of time. The very same cells that I so carefully matched to the rest exhibited the same behavior the very next time I charged them. This time though, I was watching them. But I'd say this is a clear indication that those cells simply reach their fully charged state before the others. They had not moved relative to the other cells, they just have less capacity. We're talking about a fraction of an amp/hour.
Early on, and for the first month I carefully watched the batteries every time I charged them. I saw very small differences in the finished voltages between the cells; one hundredth of a volt here, 2 hundredths there. And so it went until I had to pull the motor. After the motor was back in, they did the same thing, but I was checking them less often. I guess you could say I got complacent. I went from checking once a week, to letting it go nearly a month. When I did that last check, I found those cells I mentioned running away. There's no question they'd done it before, but there's really no way for me to determine how many times. I know it was less than 20, more than once. I also think there's no question those cells sustained some damaged by it. How much remains to be seen, but I don't think it's substantial.
I think it's likely that those cells were a slightly lower capacity than the others to start with, so they filled up first. In that 20 or so charges, they'd reach their 3.6V maximum and be forced a little higher. Each time, just a little further. In this way they accrued a little more damage each time. Had I watched them more carefully, I would have caught it. But, it is what it is, and lesson learned. Since I rarely pull more than 50% capacity from these batteries, I don't think I'll ever really feel the impact of that. Perhaps I'll get only 2900 cycles out of those cells instead of 3000.
But all of this got me thinking about battery management systems. I don't mean to imply I never thought of them before. I have, a lot. But, the ones on the market shunt off power in the form of heat when a cell reaches capacity. I can't stress enough how much I don't want that anywhere near my car. Maybe that extra heat is OK when you're in Minnesota. It's not in Arizona. No extra heat is acceptable as far as I'm concerned. I'd rather ruin a set of batteries than burn my house down.
I believe what would be ideal is a charging/battery monitoring system that has the capability of charging cells individually. A monitor on each cell would watch the cell, and when it reached it's determined state of charge, the monitor would simply shut the charging for that cell off. Not shunt the power away, but rather throw a relay that would simply stop power flowing to that cell. Of course it would need to send signal back to the charger so the charger would know that one less battery was accepting a charge. The charger would then ramp down the current it's putting out by the corresponding amount that the deactivated cell had been drawing. Otherwise, you'd have a cascade failure as more cells dropped off line, the current traveling to the remaining cells would climb until you started burning wires.
This strikes me as spectacularly complex. Doable, but due to the complexity, likely very expensive. Not only that, but complicated which means an increase in the likelihood of failure. You could certainly design the system so that failures resulted in a system shutdown, not a runaway charger. But could such a system be designed? I think so. The net result is batteries charged to the same voltage every time. This of course would be a top balanced pack. Jack Rickard has done quite a bit of work and demonstrated the dangers of top balancing. So the only way this is practical is if you simply hold the bottom 5% of the batteries state of charge as off limits. Meaning you could never run the batteries close to depleted for fear of having a cell reverse it's self.
The next best option would be similar but much more simple. A similar system with a monitor on each cell. It watches the voltage for one cell. When any cell reaches the target charge state, it sends a message to a main board that in turn trips a relay that cuts power to the charger. Sure the batteries might be at slightly different states of charge, but who cares. No battery is ever endangered and your pack is charged. The advantage to this is that you could, if you chose, bottom balance you're pack with this set up. Once balanced the charger would cut off as soon as the first battery reached it's limit and there would be no effort to move the others any further, keeping the batteries in the same positions relative to each other.
It seems to me that this would be a far simpler solution to charging and protecting your batteries and far safer than creating heat in a confined space but shunting off lots of power. I would consider putting that in my car. Heck I'd design it and build it myself if I were talented enough.
When it all comes down to it, I think my problem was one of charger set up. Setting the charger and thinking once it was tuned in nothing would change was clearly a mistake. Like I said, lesson learned.
One More Thing
Today I met with a gentleman named Alex who has been following the EV Z3 blog and the progress with the car since just before it hit the road. Alex is traveling at the moment and had a stop over here in Arizona, so we decided to take the opportunity to meet up. We had a great time. We took the car through down town Chandler, (which is unfortunately under construction) and out on the freeway. People often ask whether it can reach freeway speeds, so I thought it would be a good idea to show Alex just how well it does.
He's been considering doing a conversion of his own for a while, although his ideal car to convert is a Porsche 911. How great would that be?! Hopefully the Z3 helped to inspire him to tackle the project some day. Keep in touch Alex, and if you decide to tackle that Porsche, let me know so that I can follow the blog on your build. You will keep a blog, right? :) Thanks again!
You may remember that just over a month ago I noticed that a few of the batteries were hitting their max voltage before the others. The question became, did those cells move in their state of charge relative to the others, or do the simply have a slightly lower capacity. My assumption right away was that they'd drifted. Quite frankly, it never occurred to me that they might just have a lower capacity, which meant I immediately thought they'd moved relative to the other cells. Of course the first thing I thought to do to fix that was balance them to the others. I drew energy out of the all cells until every cell matched, down to 1/100 of a volt. I drove the car a few miles and then charged up.
That proved to be a complete waste of time. The very same cells that I so carefully matched to the rest exhibited the same behavior the very next time I charged them. This time though, I was watching them. But I'd say this is a clear indication that those cells simply reach their fully charged state before the others. They had not moved relative to the other cells, they just have less capacity. We're talking about a fraction of an amp/hour.
Early on, and for the first month I carefully watched the batteries every time I charged them. I saw very small differences in the finished voltages between the cells; one hundredth of a volt here, 2 hundredths there. And so it went until I had to pull the motor. After the motor was back in, they did the same thing, but I was checking them less often. I guess you could say I got complacent. I went from checking once a week, to letting it go nearly a month. When I did that last check, I found those cells I mentioned running away. There's no question they'd done it before, but there's really no way for me to determine how many times. I know it was less than 20, more than once. I also think there's no question those cells sustained some damaged by it. How much remains to be seen, but I don't think it's substantial.
I think it's likely that those cells were a slightly lower capacity than the others to start with, so they filled up first. In that 20 or so charges, they'd reach their 3.6V maximum and be forced a little higher. Each time, just a little further. In this way they accrued a little more damage each time. Had I watched them more carefully, I would have caught it. But, it is what it is, and lesson learned. Since I rarely pull more than 50% capacity from these batteries, I don't think I'll ever really feel the impact of that. Perhaps I'll get only 2900 cycles out of those cells instead of 3000.
But all of this got me thinking about battery management systems. I don't mean to imply I never thought of them before. I have, a lot. But, the ones on the market shunt off power in the form of heat when a cell reaches capacity. I can't stress enough how much I don't want that anywhere near my car. Maybe that extra heat is OK when you're in Minnesota. It's not in Arizona. No extra heat is acceptable as far as I'm concerned. I'd rather ruin a set of batteries than burn my house down.
I believe what would be ideal is a charging/battery monitoring system that has the capability of charging cells individually. A monitor on each cell would watch the cell, and when it reached it's determined state of charge, the monitor would simply shut the charging for that cell off. Not shunt the power away, but rather throw a relay that would simply stop power flowing to that cell. Of course it would need to send signal back to the charger so the charger would know that one less battery was accepting a charge. The charger would then ramp down the current it's putting out by the corresponding amount that the deactivated cell had been drawing. Otherwise, you'd have a cascade failure as more cells dropped off line, the current traveling to the remaining cells would climb until you started burning wires.
This strikes me as spectacularly complex. Doable, but due to the complexity, likely very expensive. Not only that, but complicated which means an increase in the likelihood of failure. You could certainly design the system so that failures resulted in a system shutdown, not a runaway charger. But could such a system be designed? I think so. The net result is batteries charged to the same voltage every time. This of course would be a top balanced pack. Jack Rickard has done quite a bit of work and demonstrated the dangers of top balancing. So the only way this is practical is if you simply hold the bottom 5% of the batteries state of charge as off limits. Meaning you could never run the batteries close to depleted for fear of having a cell reverse it's self.
The next best option would be similar but much more simple. A similar system with a monitor on each cell. It watches the voltage for one cell. When any cell reaches the target charge state, it sends a message to a main board that in turn trips a relay that cuts power to the charger. Sure the batteries might be at slightly different states of charge, but who cares. No battery is ever endangered and your pack is charged. The advantage to this is that you could, if you chose, bottom balance you're pack with this set up. Once balanced the charger would cut off as soon as the first battery reached it's limit and there would be no effort to move the others any further, keeping the batteries in the same positions relative to each other.
It seems to me that this would be a far simpler solution to charging and protecting your batteries and far safer than creating heat in a confined space but shunting off lots of power. I would consider putting that in my car. Heck I'd design it and build it myself if I were talented enough.
When it all comes down to it, I think my problem was one of charger set up. Setting the charger and thinking once it was tuned in nothing would change was clearly a mistake. Like I said, lesson learned.
One More Thing
Today I met with a gentleman named Alex who has been following the EV Z3 blog and the progress with the car since just before it hit the road. Alex is traveling at the moment and had a stop over here in Arizona, so we decided to take the opportunity to meet up. We had a great time. We took the car through down town Chandler, (which is unfortunately under construction) and out on the freeway. People often ask whether it can reach freeway speeds, so I thought it would be a good idea to show Alex just how well it does.
He's been considering doing a conversion of his own for a while, although his ideal car to convert is a Porsche 911. How great would that be?! Hopefully the Z3 helped to inspire him to tackle the project some day. Keep in touch Alex, and if you decide to tackle that Porsche, let me know so that I can follow the blog on your build. You will keep a blog, right? :) Thanks again!
Thursday, October 7, 2010
The Charger Has Returned Home
The charger arrived back from Manzanita Micro today, safe, sound and in perfect working order. They received it last Thursday, and had it fixed and on it's way back to me by Monday. I found out that it was the AC rectifier bridge that I'd damaged. They repaired that and then fully tested the unit to make sure it was healthy in all respects. The grand total in charges... $125, and $50 of that was shipping. How great is that!? I seriously hope I never have to send it back, but if I do, I know it's in great hands.
I got it back and began re-assembling the car. I hadn't done too much to it, so it only took me an hour or so. It was with some trepidation that I threw the switch to start charging the car. But it turned out my concerns were not needed. It fired up and started working like a dream.
I would still like to install the inrush limiters, or thermistors on the DC to DC converters. I bought a little project box, meaning to do it during this week's down time. But I found out more about they way they work which forced me to change my plans. When cold, they offer high resistance to the current, which keeps the arcing to a minimum, but they quickly heat up as current flows through them and the resistance drops. It's not unusual for them to reach 200° F. Well the project box I bought was plastic, so that wouldn't do. But worse, the only place I have to mount them is against the plastic box in the trunk that holds the charger and DC to DC converters.
So, I need to re-think how I'm going to do that, and where I'm going to mount them. I'm kind of at a loss right now, but I'll figure something out eventually. I could disassemble the DC to DC converters and actually put them inside the housing, but I really don't want to do that. Regardless, tomorrow I'm back on the road with a nice big EV grin!
COMPLETELY OFF TOPIC
A friend of mine named Fred and I have launched a new blog. It is called F1-Geeks, and as you might have guessed, it's devoted to Formula 1. But that's not all! We actually intend to talk about several topics that we and others like us find particularly interesting; cars, gaming, tech gadgets, home theater stuff and EV stuff too. Check it out, and leave us a comment or two if you feel like it. Thanks!
I got it back and began re-assembling the car. I hadn't done too much to it, so it only took me an hour or so. It was with some trepidation that I threw the switch to start charging the car. But it turned out my concerns were not needed. It fired up and started working like a dream.
I would still like to install the inrush limiters, or thermistors on the DC to DC converters. I bought a little project box, meaning to do it during this week's down time. But I found out more about they way they work which forced me to change my plans. When cold, they offer high resistance to the current, which keeps the arcing to a minimum, but they quickly heat up as current flows through them and the resistance drops. It's not unusual for them to reach 200° F. Well the project box I bought was plastic, so that wouldn't do. But worse, the only place I have to mount them is against the plastic box in the trunk that holds the charger and DC to DC converters.
So, I need to re-think how I'm going to do that, and where I'm going to mount them. I'm kind of at a loss right now, but I'll figure something out eventually. I could disassemble the DC to DC converters and actually put them inside the housing, but I really don't want to do that. Regardless, tomorrow I'm back on the road with a nice big EV grin!
COMPLETELY OFF TOPIC
A friend of mine named Fred and I have launched a new blog. It is called F1-Geeks, and as you might have guessed, it's devoted to Formula 1. But that's not all! We actually intend to talk about several topics that we and others like us find particularly interesting; cars, gaming, tech gadgets, home theater stuff and EV stuff too. Check it out, and leave us a comment or two if you feel like it. Thanks!
Wednesday, September 29, 2010
Insulation
Here we have a nice shot of the damage caused to the terminal when my meter's probe slipped off the top of the nut and shorted against the base of the terminal and that aluminum angle piece to the right.
Clearly, I couldn't leave it like that. Being as clumsy as I am, it's bound to happen again as long as that aluminum perches so dangerously close to those terminals. I can't move the angle aluminum because it's what's holding the batteries in the car. I figured the best thing to do was to put some sort of rubber insulation on the aluminum to keep any accidental shorts from occurring. So, I went down to the local hardware store to look for a sheet of rubber. What I ended up finding was a sheet of PVC used for lining the floor under a shower pan. Waterproof, flexible, and more importantly, electrically non-conductive. It's sold by the linear foot, and one foot of the stuff cost me less than $6.
I cut a few carefully measured strips from the sheet and painted some contact adhesive on one side.
I masked off the angle aluminum as best I could and painted those with the adhesive as well. After a couple hours of drying time I carefully stuck the strips to the aluminum.
It stuck on very well and should do the job. I had cut the strips so that I could wrap them around the bend, hoping that the sheet would stick to the inside edge's 1/8" surface of the aluminum. But the material simply isn't flexible enough to make that bend. If I could find a sheet of real rubber, and if it were thin enough, it would make that bend, but I think this will work fine. Take a look, there's no way to short the terminals against those aluminum pieces by accident.
Clearly, I couldn't leave it like that. Being as clumsy as I am, it's bound to happen again as long as that aluminum perches so dangerously close to those terminals. I can't move the angle aluminum because it's what's holding the batteries in the car. I figured the best thing to do was to put some sort of rubber insulation on the aluminum to keep any accidental shorts from occurring. So, I went down to the local hardware store to look for a sheet of rubber. What I ended up finding was a sheet of PVC used for lining the floor under a shower pan. Waterproof, flexible, and more importantly, electrically non-conductive. It's sold by the linear foot, and one foot of the stuff cost me less than $6.
I cut a few carefully measured strips from the sheet and painted some contact adhesive on one side.
I masked off the angle aluminum as best I could and painted those with the adhesive as well. After a couple hours of drying time I carefully stuck the strips to the aluminum.
It stuck on very well and should do the job. I had cut the strips so that I could wrap them around the bend, hoping that the sheet would stick to the inside edge's 1/8" surface of the aluminum. But the material simply isn't flexible enough to make that bend. If I could find a sheet of real rubber, and if it were thin enough, it would make that bend, but I think this will work fine. Take a look, there's no way to short the terminals against those aluminum pieces by accident.
Monday, September 27, 2010
Chargers Away
One of the tough things about building this car was the extremely tight spaces I had to work with and in. Getting my arms back there to turn the screws and bolts that held the charger in was so difficult. It took me the better part of an hour, but I finally liberated the charger from it's home.
Here's the charger, which looks totally fine.
I packaged it up very carefully and handed it to UPS this afternoon. In an email exchange with Rich from Manzanita, he said that assuming nothing other than the input AC rectifier is damaged, they should be able to fix it up in a day or two for around $200. How great is that?!
As I've mentioned before, I need to raise the height of the front of the car. I found a place that will build new springs for me, but they want one of the springs and some measurements off of the front suspension. Well, I can't take a spring off the car and mail it away, I'm using them at the moment. While looking around on eBay for a spare spring I can send off to Kansas, I came across an item that I had always felt sure must have existed, but I'd never seen. A quick search in Google and I found these items.
These are spacers that you can slip between the coils of a spring to give it up to a 1" lift. The springs on the Z3 were already riding low when I bought the car. The car was riding about 3/4" lower than stock. With the extra weight of the batteries and motor, it dropped another 3/4".
I took a look at the springs and the bottom 2 coils were very close to each other. I jacked the car up one side at a time and slipped them in, wedging them as far down in the coil as I could. I sat the car back down, drove it around a bit and then measured the ride height. It gained 2cm, or .79". That's more than I lost from doing the conversion. It looks much better too.
Of course that means I've lost a bit of spring travel, but not 2 cm since the gap I squeezed the rubber piece into was more like 1 cm high when the car was on the ground. The real question is will that loss of 1 cm of spring travel cause me problems. I don't think it will, I already drive it very carefully and slowly over bumps. But it's the bumps you don't see that get you. The good thing is that if the spring should collapse all the way, that big grommet is rubber and will flex. Hopefully enough to protect the pillar.
I think it's a good band-aid solution, but I'm going to continue my efforts to get the car sprung properly.
Here's the charger, which looks totally fine.
I packaged it up very carefully and handed it to UPS this afternoon. In an email exchange with Rich from Manzanita, he said that assuming nothing other than the input AC rectifier is damaged, they should be able to fix it up in a day or two for around $200. How great is that?!
As I've mentioned before, I need to raise the height of the front of the car. I found a place that will build new springs for me, but they want one of the springs and some measurements off of the front suspension. Well, I can't take a spring off the car and mail it away, I'm using them at the moment. While looking around on eBay for a spare spring I can send off to Kansas, I came across an item that I had always felt sure must have existed, but I'd never seen. A quick search in Google and I found these items.
These are spacers that you can slip between the coils of a spring to give it up to a 1" lift. The springs on the Z3 were already riding low when I bought the car. The car was riding about 3/4" lower than stock. With the extra weight of the batteries and motor, it dropped another 3/4".
I took a look at the springs and the bottom 2 coils were very close to each other. I jacked the car up one side at a time and slipped them in, wedging them as far down in the coil as I could. I sat the car back down, drove it around a bit and then measured the ride height. It gained 2cm, or .79". That's more than I lost from doing the conversion. It looks much better too.
Of course that means I've lost a bit of spring travel, but not 2 cm since the gap I squeezed the rubber piece into was more like 1 cm high when the car was on the ground. The real question is will that loss of 1 cm of spring travel cause me problems. I don't think it will, I already drive it very carefully and slowly over bumps. But it's the bumps you don't see that get you. The good thing is that if the spring should collapse all the way, that big grommet is rubber and will flex. Hopefully enough to protect the pillar.
I think it's a good band-aid solution, but I'm going to continue my efforts to get the car sprung properly.
Thursday, September 23, 2010
Something Stupid
Just when everything is going well...
I've been making slow progress zeroing in on getting the charger set to bring the batteries up to the optimal charge point before it turns off. It's tough because the charger uses a little screw potentiometer to adjust it up and down. It's exceedingly difficult to get it right where you want it. Plus I've found that if you change the current you're pushing to the pack, the high voltage point at which the charger believes it's done changes.
When I have the charger turned up all the way so that it's pushing 28 amps, it would cut off at 164.5 volts. But if I ramp the current down to 10 amps, it trips off at 165.8 volts. It would be so much nicer if the charger had a digital interface for setting the cut off voltage. I realize that would add to the cost of the charger, but I have to tell you, I'd pay for it.
This morning I was charging the car at 10 amps The charger hit it's limit threshold at 164.7, which is about where I want it. I started taking measurements on the cells to monitor how they were doing. There are a couple that come up to 3.6 volts faster than the others. While measuring one of the cells I slipped and touched the probe to the chassis while it was on the positive terminal for that cell. Well, there was a loud pop, and a nice bright flash. When I looked down, the point on the end of my probe had been melted to a nice rounded blob, the terminal had a big black spot around it, and the charger had flipped off.
I checked everything and couldn't find any obvious problems to any of the systems. I tried to turn the charger back on, but there was no power to the charger; the breaker for the outlet had popped too. I reset it and tried to turn the charger on again. Loud pop, but no flash anywhere, and the charger tripped it's breaker and the breaker on the house tripped too. *Sigh*
So it would seem that through clumsiness or carelessness, I've damaged my charger. I've sent an email off to Rich Rudman at Manzanita Micro to get his advice. But I'm pretty sure that the chargers coming out of the car soon and making a trip to Washington. Man I hate it when I do stupid stuff. And just as the weather is really getting beautiful for top down driving! *Sigh*
UPDATE:
I heard back from Rich at Manzanita. Apparently I've blown the input AC rectifier. So, I'll be taking the charger out of the car ASAP and sending it back to them for repair.
I've been making slow progress zeroing in on getting the charger set to bring the batteries up to the optimal charge point before it turns off. It's tough because the charger uses a little screw potentiometer to adjust it up and down. It's exceedingly difficult to get it right where you want it. Plus I've found that if you change the current you're pushing to the pack, the high voltage point at which the charger believes it's done changes.
When I have the charger turned up all the way so that it's pushing 28 amps, it would cut off at 164.5 volts. But if I ramp the current down to 10 amps, it trips off at 165.8 volts. It would be so much nicer if the charger had a digital interface for setting the cut off voltage. I realize that would add to the cost of the charger, but I have to tell you, I'd pay for it.
This morning I was charging the car at 10 amps The charger hit it's limit threshold at 164.7, which is about where I want it. I started taking measurements on the cells to monitor how they were doing. There are a couple that come up to 3.6 volts faster than the others. While measuring one of the cells I slipped and touched the probe to the chassis while it was on the positive terminal for that cell. Well, there was a loud pop, and a nice bright flash. When I looked down, the point on the end of my probe had been melted to a nice rounded blob, the terminal had a big black spot around it, and the charger had flipped off.
I checked everything and couldn't find any obvious problems to any of the systems. I tried to turn the charger back on, but there was no power to the charger; the breaker for the outlet had popped too. I reset it and tried to turn the charger on again. Loud pop, but no flash anywhere, and the charger tripped it's breaker and the breaker on the house tripped too. *Sigh*
So it would seem that through clumsiness or carelessness, I've damaged my charger. I've sent an email off to Rich Rudman at Manzanita Micro to get his advice. But I'm pretty sure that the chargers coming out of the car soon and making a trip to Washington. Man I hate it when I do stupid stuff. And just as the weather is really getting beautiful for top down driving! *Sigh*
UPDATE:
I heard back from Rich at Manzanita. Apparently I've blown the input AC rectifier. So, I'll be taking the charger out of the car ASAP and sending it back to them for repair.
Friday, September 17, 2010
More Battery Info
I've spent the last week and a half working with the batteries and charger, trying to fine tune and develop a charging plan. The more I've worked on this, the more I'm starting to think the problems I've encountered up to this point were simply a result of setting charger's cutoff voltage too high.
Initially I'd set it at 168 volts, because that's the target voltage I wanted (3.5 x 48). But of course, that was too high because the charger simply begins it's ramp down of current at that level. That lasted one charge, then I turned it down to 166.5. That worked out well as the voltage on the pack was at 168 when the charger finally cut off.
But clearly as the cells broke in, or started showing their individuality, some started reaching their target voltage before others. In terms of actual current pushed to the cell, the differences are so small. In the last post, I'd figured that the difference between the extremes was about 7.3 Watt hours. That may actually be a bit high. It may be closer to 5 Watt hours.
I lowered the chargers cutoff to 165 volts, and that seemed to be working quite well. That put the finishing voltage at around 166.8 volts. The batteries prone to runaway were hitting about 3.58 volts, by the time the charger kicked off. The rest of the cells were only just behind. The difference in the entire pack's charge state reduced by only 150 Watt hours or so. But on two occasions, I saw one of the cells climb to 3.60 volts when there was around a minute left on the charging cycle. Had I let it go, they would have climbed to somewhere close to 3.64 Clearly, I needed to back it off just a bit more.
This morning, I charged the pack with the charger starting it's ramp down at 164.5 volts. It finished at 166.3 volts, with the highest cell at 3.52 volts and the lowest at 3.43. That, I think, will be just fine if we get something like that each time. I'll continue monitoring over the next few weeks to see how things progress, but it's looking good at the moment. As best I can figure, that cost me another 100 Watt hours. So I'm down my a grand total of 250 Watt hours in the pack. Less than one mile.
Springs
I had a local shop look at the springs on the car Tuesday. Since the car was riding 3/4" lower than stock when I got it, I had always wondered if it had received aftermarket springs to lower it, or if the original springs were just tired. They invited me down to take a look. Turns out they are the originals, which means I have two options. I could get coil overs for around $1500. Or I could have some springs made. A place out of Kansas City will fabricate new springs for me which will take the proper weight, if I send them one of my springs, some geometry measurements off the suspension, the new weight of the car and $285. Sounds like a good deal to me, but I'm not in a position to take a spring off my car. I need to find one at a local salvage yard. Over all the car is riding 1.5" lower than stock, but just on the front end. The back end is perfect. I look like I'm going down hill all the time.
Plates
The good people at ADOT have seen fit to grant my request for a custom license plate. Check it out!
How sweet is that?!
Initially I'd set it at 168 volts, because that's the target voltage I wanted (3.5 x 48). But of course, that was too high because the charger simply begins it's ramp down of current at that level. That lasted one charge, then I turned it down to 166.5. That worked out well as the voltage on the pack was at 168 when the charger finally cut off.
But clearly as the cells broke in, or started showing their individuality, some started reaching their target voltage before others. In terms of actual current pushed to the cell, the differences are so small. In the last post, I'd figured that the difference between the extremes was about 7.3 Watt hours. That may actually be a bit high. It may be closer to 5 Watt hours.
I lowered the chargers cutoff to 165 volts, and that seemed to be working quite well. That put the finishing voltage at around 166.8 volts. The batteries prone to runaway were hitting about 3.58 volts, by the time the charger kicked off. The rest of the cells were only just behind. The difference in the entire pack's charge state reduced by only 150 Watt hours or so. But on two occasions, I saw one of the cells climb to 3.60 volts when there was around a minute left on the charging cycle. Had I let it go, they would have climbed to somewhere close to 3.64 Clearly, I needed to back it off just a bit more.
This morning, I charged the pack with the charger starting it's ramp down at 164.5 volts. It finished at 166.3 volts, with the highest cell at 3.52 volts and the lowest at 3.43. That, I think, will be just fine if we get something like that each time. I'll continue monitoring over the next few weeks to see how things progress, but it's looking good at the moment. As best I can figure, that cost me another 100 Watt hours. So I'm down my a grand total of 250 Watt hours in the pack. Less than one mile.
Springs
I had a local shop look at the springs on the car Tuesday. Since the car was riding 3/4" lower than stock when I got it, I had always wondered if it had received aftermarket springs to lower it, or if the original springs were just tired. They invited me down to take a look. Turns out they are the originals, which means I have two options. I could get coil overs for around $1500. Or I could have some springs made. A place out of Kansas City will fabricate new springs for me which will take the proper weight, if I send them one of my springs, some geometry measurements off the suspension, the new weight of the car and $285. Sounds like a good deal to me, but I'm not in a position to take a spring off my car. I need to find one at a local salvage yard. Over all the car is riding 1.5" lower than stock, but just on the front end. The back end is perfect. I look like I'm going down hill all the time.
Plates
The good people at ADOT have seen fit to grant my request for a custom license plate. Check it out!
How sweet is that?!
Thursday, September 9, 2010
First Charge After Balancing
Yesterday I drew off about 5 kWhs from the battery pack while driving the car around. This was after I had balanced it the day before. So I was all set to charge the pack to find out how the cells behave.
Before I get to that though, I had been in contact with Jack Rickard letting him know of the imbalance in the pack. Jack is the champion of the "No BMS necessary" movement. He warned me of dangers involved in "top balancing" the pack. For those of you unaware, the concept here is that there is far more danger involved in having the state of the cells differ while down at the bottom of the charge curve, than while at the top. The danger being that if one cell drops below the 2.0 voltage limit, the others will drive it into death very quickly.
I believe this to be a real threat, Jack's tests have demonstrated this. But for the moment, I'm not worried about cell behavior at the bottom of the curve as I'm not taking them there. I am worried about what they're doing at the top because that's where I'm seeing the discrepancy. But it looks like that concern may be misplaced.
When I charged the pack last night, I watched as all the batteries marched up the voltage curve in nice even step. They all arrived at 3.38 volts together. But then a few of them hit 3.39 while others lagged behind. There was one cell in particular that started climbing faster than the rest. When that cell hit 3.50 volts, the others were around 3.44, plus or minus .02 volts. I watched carefully until that one cell hit 3.60 and I killed the charger. By that time the others were around 3.49 volts.
So now I think I know what's happening. I have my charger set to cut off when the pack reaches 165 volts. Or rather, it starts ramping down the current when it gets there. The idea being that it stops charging when the pack is at 168 volts. That would put each cell at 3.5 volts. Early on I had made the assumption that the cells that were coming up too fast had shifted in the pack, that their state of charge had moved relative to the others. I don't think this was the case.
Jack had pointed out that another possibility is these cells have developed a diminished capacity. Well, I think that is the likely explanation as sad as that is. Think of the batteries as if they were a jar you poured fluid in. If one jar in the mix suddenly has a little less capacity (you've dropped a rock in it) when you're adding water to them all evenly, one will start to overflow before the others. What is clear is that it wasn't a result of cell drift within the pack because balancing them would have resolved the difference. The question at this point is how much has this rogue cell lost?
Keeping in mind the characteristics of these cells to runaway very quickly at the top and bottom of the charge curve, what I need to do is figure out how much more time would be required to fill the rest of the batteries after this one was charged completely. Based on what I was seeing during that last charge, I'd place that at about 5 minutes. I know that each cell has 408 Watt hours (120 Ah x 3.4 volts). During charging, each cell gets 1.46 Watts per minute. So if this cell is full 5 minutes before the others, that means it's capacity is 7.3 Watt hours below the others, or 1.8%. It also means that if I cut off the charger when that cell has reached it's peak, the rest are missing out on that 5 minutes of charging, which translates into 350 Watt hours, or one mile of travel (at this time).
To the best of my knowledge, all this is correct; however, I'm not above making boneheaded mistakes, as anyone who reads this blog can attest to. But all of this raises a few questions. The most obvious is would a BMS help the situation. I think it would, but there are trade offs I'm not comfortable with. The first being the cost. The second being the fact that the extra power to the cells which reach their capacity first is simply shunted off as heat. No thanks, it's already 110 °F in my garage. There's no way I'm risking setting my car on fire. To me, that negates all the benefits that come with the slight reduction in worry to the health of the pack.
Besides, at this point, what's it going to gain me? It would seem one mile. If I wanted to be extra sure I'm not endangering the pack, I could dial the charger back a bit more, reduce my range by say 5 miles and really ensure there's no risk to the pack! I've got 60 miles to play with, what's 5? Nope, still not seeing a compelling reason to add a BMS.
The other question is would it be worth going through the process of bottom balancing the pack? I'm not entirely sure what it would gain me at this point. It would make longer trips safer for the batteries as they'd all meet their discharge point at the same time. But I never really drive the car more than 40 miles at a time, usually only 25. That's something I'll reserve for some future time.
For now, I need to fine tune my charger to be sure and protect that cell. The others that weren't far behind it in voltage during last Friday's charge are presumably in the same boat, but not as bad. It stands to reason, if I charge the pack being sure to protect that cell from over charge, the rest are safe. Still, I'm going to have to watch them all for any further deviation.
Before I get to that though, I had been in contact with Jack Rickard letting him know of the imbalance in the pack. Jack is the champion of the "No BMS necessary" movement. He warned me of dangers involved in "top balancing" the pack. For those of you unaware, the concept here is that there is far more danger involved in having the state of the cells differ while down at the bottom of the charge curve, than while at the top. The danger being that if one cell drops below the 2.0 voltage limit, the others will drive it into death very quickly.
I believe this to be a real threat, Jack's tests have demonstrated this. But for the moment, I'm not worried about cell behavior at the bottom of the curve as I'm not taking them there. I am worried about what they're doing at the top because that's where I'm seeing the discrepancy. But it looks like that concern may be misplaced.
When I charged the pack last night, I watched as all the batteries marched up the voltage curve in nice even step. They all arrived at 3.38 volts together. But then a few of them hit 3.39 while others lagged behind. There was one cell in particular that started climbing faster than the rest. When that cell hit 3.50 volts, the others were around 3.44, plus or minus .02 volts. I watched carefully until that one cell hit 3.60 and I killed the charger. By that time the others were around 3.49 volts.
So now I think I know what's happening. I have my charger set to cut off when the pack reaches 165 volts. Or rather, it starts ramping down the current when it gets there. The idea being that it stops charging when the pack is at 168 volts. That would put each cell at 3.5 volts. Early on I had made the assumption that the cells that were coming up too fast had shifted in the pack, that their state of charge had moved relative to the others. I don't think this was the case.
Jack had pointed out that another possibility is these cells have developed a diminished capacity. Well, I think that is the likely explanation as sad as that is. Think of the batteries as if they were a jar you poured fluid in. If one jar in the mix suddenly has a little less capacity (you've dropped a rock in it) when you're adding water to them all evenly, one will start to overflow before the others. What is clear is that it wasn't a result of cell drift within the pack because balancing them would have resolved the difference. The question at this point is how much has this rogue cell lost?
Keeping in mind the characteristics of these cells to runaway very quickly at the top and bottom of the charge curve, what I need to do is figure out how much more time would be required to fill the rest of the batteries after this one was charged completely. Based on what I was seeing during that last charge, I'd place that at about 5 minutes. I know that each cell has 408 Watt hours (120 Ah x 3.4 volts). During charging, each cell gets 1.46 Watts per minute. So if this cell is full 5 minutes before the others, that means it's capacity is 7.3 Watt hours below the others, or 1.8%. It also means that if I cut off the charger when that cell has reached it's peak, the rest are missing out on that 5 minutes of charging, which translates into 350 Watt hours, or one mile of travel (at this time).
To the best of my knowledge, all this is correct; however, I'm not above making boneheaded mistakes, as anyone who reads this blog can attest to. But all of this raises a few questions. The most obvious is would a BMS help the situation. I think it would, but there are trade offs I'm not comfortable with. The first being the cost. The second being the fact that the extra power to the cells which reach their capacity first is simply shunted off as heat. No thanks, it's already 110 °F in my garage. There's no way I'm risking setting my car on fire. To me, that negates all the benefits that come with the slight reduction in worry to the health of the pack.
Besides, at this point, what's it going to gain me? It would seem one mile. If I wanted to be extra sure I'm not endangering the pack, I could dial the charger back a bit more, reduce my range by say 5 miles and really ensure there's no risk to the pack! I've got 60 miles to play with, what's 5? Nope, still not seeing a compelling reason to add a BMS.
The other question is would it be worth going through the process of bottom balancing the pack? I'm not entirely sure what it would gain me at this point. It would make longer trips safer for the batteries as they'd all meet their discharge point at the same time. But I never really drive the car more than 40 miles at a time, usually only 25. That's something I'll reserve for some future time.
For now, I need to fine tune my charger to be sure and protect that cell. The others that weren't far behind it in voltage during last Friday's charge are presumably in the same boat, but not as bad. It stands to reason, if I charge the pack being sure to protect that cell from over charge, the rest are safe. Still, I'm going to have to watch them all for any further deviation.
Tuesday, September 7, 2010
Battery Balance
I'd hoped this day wouldn't come, and that this problem wouldn't occur, but it has. I was charging the batteries last Friday and I found a couple of them heading North of the target 3.5 Volts. CALB (the manufacturer of these cells) recommends that you charge them to no higher than 3.6 volts. You can imagine my concern when I found 4 of them higher than 3.8! Well, that just won't do, and if that continues, I'll shorten the life expectancy of these rather expensive batteries.
Now, I know what some of you are saying. "Of course you idiot, you're not using a BMS. You must use a BMS with these cells, what did you expect!?" To you folks I say you're right. Sort of.
There is no question that these, and in fact all batteries need battery management of some sort. The conventional wisdom regarding LiFePo4 cells is that you must use an automated BMS to protect them from overcharging. But, keep in mind that even lead acid batteries need BMS. The primary difference being that people tend to manage lead acid batteries manually, watering them and equalizing them on occasion. As I see it, the real question is whether you need an expensive automated BMS system for these LiFePo4 cells, or can you manage them yourself like you would lead acid batteries?
So far these batteries have been really boring. They've all charged up to 3.5 volts reliably and stayed in balance nicely. Keep in mind that after you remove the charger current and let the cells settle, they end up around 3.4 Volts. Their stability had lulled me into complacency and I hadn't checked the individual cells while charging for a month or so. In that time, a few of them drifted. I don't know why; the heat in the garage, bad connections, differences within the cells themselves? Chances are I'll never know, and in all likelihood they'll do it again.
Right now I'm equalizing them, getting each battery down to 3.350 Volts. This is a long, boring procedure, but not particularly difficult. I've simply hooked a 12 volt brake light to some alligator clamps. I clamp the meter to the posts and then the bulb. The bulb glows and burns off the extra electricity. It's just a question of stepping through each cell. About half are at the right voltage already. The rest are within 0.05 Volts, except the 4 naughty ones that were at 3.6 after resting, or .25 Volts too high. Like I said, not difficult, just boring. You must pay close attention.
Now the question becomes how often am I going to have to do this. Lets assume that it's in their very nature for the batteries to do this. Then how often will they drift? What's the rate of drift? Can I expect them to fall out of balance on the very first charge, or will it take 6 months? Will it be a gradual change, or will it happen within one charging session? The answer to these questions really determines the risk that the batteries face and whether I'm going to need to give in and get a BMS.
If the past 7 months can be used as a baseline, I'm thinking that I may be able to go 4 months before I need to worry about balancing them. Remember there was about 2 months of down time when I had to remove the motor. If I really can wait 4 months before I need to take action, then I'd say a BMS is not necessary. However, if I charge them up tomorrow and see some of the cells immediately going higher than 3.5 volts, that likely means that the only way to prevent that is a BMS system. If the mean time to imbalance (mti, for all us geeks who live in a world of three letter acronyms) is somewhere in between those two figures, then it just becomes a question of weighing the inconvenience involved in manually balancing them, and how often I have to do it. Not to mention whether I'm willing to endure the pain of having to regularly measure the cells close to the end of a charging cycle.
One thing is certain, and that is I'm going to have to monitor them very closely over the next several months to get a clear idea of what's happening and when. In either case, I intend to protect these cells from that kind of event again. Along the way, I'll record what I'm seeing here. Those of you who care to follow along may learn a thing or two about the cells and how they behave. I may find a BMS is essential. Or I may find that with a little care, you can do just fine without one. Apart from the fact that I'd rather not spend somewhere around $3,000 for a BMS, I have no passion for one position over the other.
Now, I know what some of you are saying. "Of course you idiot, you're not using a BMS. You must use a BMS with these cells, what did you expect!?" To you folks I say you're right. Sort of.
There is no question that these, and in fact all batteries need battery management of some sort. The conventional wisdom regarding LiFePo4 cells is that you must use an automated BMS to protect them from overcharging. But, keep in mind that even lead acid batteries need BMS. The primary difference being that people tend to manage lead acid batteries manually, watering them and equalizing them on occasion. As I see it, the real question is whether you need an expensive automated BMS system for these LiFePo4 cells, or can you manage them yourself like you would lead acid batteries?
So far these batteries have been really boring. They've all charged up to 3.5 volts reliably and stayed in balance nicely. Keep in mind that after you remove the charger current and let the cells settle, they end up around 3.4 Volts. Their stability had lulled me into complacency and I hadn't checked the individual cells while charging for a month or so. In that time, a few of them drifted. I don't know why; the heat in the garage, bad connections, differences within the cells themselves? Chances are I'll never know, and in all likelihood they'll do it again.
Right now I'm equalizing them, getting each battery down to 3.350 Volts. This is a long, boring procedure, but not particularly difficult. I've simply hooked a 12 volt brake light to some alligator clamps. I clamp the meter to the posts and then the bulb. The bulb glows and burns off the extra electricity. It's just a question of stepping through each cell. About half are at the right voltage already. The rest are within 0.05 Volts, except the 4 naughty ones that were at 3.6 after resting, or .25 Volts too high. Like I said, not difficult, just boring. You must pay close attention.
Now the question becomes how often am I going to have to do this. Lets assume that it's in their very nature for the batteries to do this. Then how often will they drift? What's the rate of drift? Can I expect them to fall out of balance on the very first charge, or will it take 6 months? Will it be a gradual change, or will it happen within one charging session? The answer to these questions really determines the risk that the batteries face and whether I'm going to need to give in and get a BMS.
If the past 7 months can be used as a baseline, I'm thinking that I may be able to go 4 months before I need to worry about balancing them. Remember there was about 2 months of down time when I had to remove the motor. If I really can wait 4 months before I need to take action, then I'd say a BMS is not necessary. However, if I charge them up tomorrow and see some of the cells immediately going higher than 3.5 volts, that likely means that the only way to prevent that is a BMS system. If the mean time to imbalance (mti, for all us geeks who live in a world of three letter acronyms) is somewhere in between those two figures, then it just becomes a question of weighing the inconvenience involved in manually balancing them, and how often I have to do it. Not to mention whether I'm willing to endure the pain of having to regularly measure the cells close to the end of a charging cycle.
One thing is certain, and that is I'm going to have to monitor them very closely over the next several months to get a clear idea of what's happening and when. In either case, I intend to protect these cells from that kind of event again. Along the way, I'll record what I'm seeing here. Those of you who care to follow along may learn a thing or two about the cells and how they behave. I may find a BMS is essential. Or I may find that with a little care, you can do just fine without one. Apart from the fact that I'd rather not spend somewhere around $3,000 for a BMS, I have no passion for one position over the other.
Wednesday, August 18, 2010
Getting Some Driving Time
The heat here in Phoenix is letting up a bit. Not enough to comfortably drive the car in the middle of the day, but early and mid-mornings have been very nice. Every morning I take the car out for a daily errand, and it's just fabulous. What a great car to drive!
Back before I had to remove the motor, I was giving a friend a ride around the neighborhood to show him the car. I drove by a neighbor that lives around the corner, he and his daughter were in the street playing catch. As we approached, I was worried they might not know we were coming, but they saw us and moved aside and we all waved as we went by.
When we came back by, I slowed down to be sure we were all safe, and the father called out "Is that an electric car?" I told him it was, and he said that he knew it had to be because it hadn't made any noise when we first drove by. I stopped for a few minutes to chat. He had a lot of questions about the car, and seemed truly interested. I answered them all as best I could and waved goodbye.
Over the past few days, since I've been driving it more, I've happened by him a few more times. Each time he eagerly waves and smiles. It's great to have made a connection with a neighbor, I hope to talk to him more and maybe offer a ride someday. But the best thing is that he's seeing an electric car driving around the neighborhood on a regular basis, and he has a positive attitude about it. I hope that it's situations like this that will slowly help to convince more and more people that an electric car IS a viable option for some.
I'm still averaging about 325 Watt/hours per mile, which isn't horrible, but I'm pretty sure that will get better with the modifications I've planned for this fall. New springs in the front, fix the alignment and replace the differential's fluid are what I have in store as soon as the weather really starts cooling off.
There is one small thing that's been driving me crazy, and that is a rattle coming from the rear of the car. A rattle whose source, I've not been able to locate. It only happens when I'm heading over bumps, so at least it's not constant. I've looked for it repeatedly, driving the car up on the ramps and poking and prodding, but with no luck. It has a real tinny sound, so it's something small, and I thought I knew exactly what it was. It sounds like one of the clamps used to compress the batteries in the rear battery box is loose. But I've checked them all, and they are all nice and tight.
It's definitely coming from the back end though. The funny thing is, no one else notices it until I point it out. Then they all say something like "It's not that bad." They're right, it isn't, but it drives me nuts. I'm going to have to drive up the ramps again and really give the back end a thorough inspection. I'm not worried that anything is going to fall off or come undone. I used self locking nuts on all the connections in the car; the kind that can't spin off on their own. Eventually I'll find it. I just hope it's before I go mad.
I'm going out to the Diamondbacks baseball game tonight with a friend. I'd love to drive the car there, but the heat would make that an unpleasant drive. The real sad thing is that the ball park has removed their electric car parking spaces! They had 2 spaces in one of the closest parking structures, right up front, with charging stations and everything. I called to find out if they were still there and what was involved in using them, only to be told that they'd been removed. Sadly, the last time I went there, I found they had indeed been turned into handicapped spaces. *Sigh* I can't really blame them, they were empty every game, but what lousy timing!
Back before I had to remove the motor, I was giving a friend a ride around the neighborhood to show him the car. I drove by a neighbor that lives around the corner, he and his daughter were in the street playing catch. As we approached, I was worried they might not know we were coming, but they saw us and moved aside and we all waved as we went by.
When we came back by, I slowed down to be sure we were all safe, and the father called out "Is that an electric car?" I told him it was, and he said that he knew it had to be because it hadn't made any noise when we first drove by. I stopped for a few minutes to chat. He had a lot of questions about the car, and seemed truly interested. I answered them all as best I could and waved goodbye.
Over the past few days, since I've been driving it more, I've happened by him a few more times. Each time he eagerly waves and smiles. It's great to have made a connection with a neighbor, I hope to talk to him more and maybe offer a ride someday. But the best thing is that he's seeing an electric car driving around the neighborhood on a regular basis, and he has a positive attitude about it. I hope that it's situations like this that will slowly help to convince more and more people that an electric car IS a viable option for some.
I'm still averaging about 325 Watt/hours per mile, which isn't horrible, but I'm pretty sure that will get better with the modifications I've planned for this fall. New springs in the front, fix the alignment and replace the differential's fluid are what I have in store as soon as the weather really starts cooling off.
There is one small thing that's been driving me crazy, and that is a rattle coming from the rear of the car. A rattle whose source, I've not been able to locate. It only happens when I'm heading over bumps, so at least it's not constant. I've looked for it repeatedly, driving the car up on the ramps and poking and prodding, but with no luck. It has a real tinny sound, so it's something small, and I thought I knew exactly what it was. It sounds like one of the clamps used to compress the batteries in the rear battery box is loose. But I've checked them all, and they are all nice and tight.
It's definitely coming from the back end though. The funny thing is, no one else notices it until I point it out. Then they all say something like "It's not that bad." They're right, it isn't, but it drives me nuts. I'm going to have to drive up the ramps again and really give the back end a thorough inspection. I'm not worried that anything is going to fall off or come undone. I used self locking nuts on all the connections in the car; the kind that can't spin off on their own. Eventually I'll find it. I just hope it's before I go mad.
I'm going out to the Diamondbacks baseball game tonight with a friend. I'd love to drive the car there, but the heat would make that an unpleasant drive. The real sad thing is that the ball park has removed their electric car parking spaces! They had 2 spaces in one of the closest parking structures, right up front, with charging stations and everything. I called to find out if they were still there and what was involved in using them, only to be told that they'd been removed. Sadly, the last time I went there, I found they had indeed been turned into handicapped spaces. *Sigh* I can't really blame them, they were empty every game, but what lousy timing!
Tuesday, August 10, 2010
Interesting Results
Over the weekend, I ran the final test (for now) on the high voltage system. I hooked up the last piece of equipment to be tested, the DC to DC converters, and let the car sit for 3 days. By the end of the three days, the Link-10 showed that 2.18 kW-hs had been drawn off the pack. For those of you keeping track, you'll recognize that number as being very close to what we've seen in the past. Indeed, previous tests have all come up showing 2.15 kW-hs over the same time period. I'd mentioned that I expected this test to be a bit different because the fans for the DC to DC converters run continuously due to the ambient air temperature. So, at first glance it looks like we're seeing that difference. The interesting thing is what happened when I charge the pack.
On prior tests, the meter showed that the pack had lost 2.15 kW-hs, only to find when I charged the pack it would only accept around 200 W-hs. When I've worked out the math each time, I found that the Link-10 was introducing a about a 700 W-h per day error. If you want to be precise, it's actually 650 W-hs, but I rounded up 700 because it's easier for me to remember and for a few other reasons that would simply put you to sleep if I enumerated them.
Anyway, this time proved to be a bit different. I plugged in the car, started up the charger and stood there waiting for the charger to indicate it was done. I figured it would take 5, 10 minutes max. Well, after waiting for 15 minutes, and watching over a 1 kW-h be pushed to the pack, I realized that this wasn't going the way I'd expected. By the time the charger finally kicked off, it had pushed a total of 1.53 kW-hs into the battery.
Even though the Link-10 showed nearly the same draw over the 3 day test as it did on every other test, there had actually been a real draw off the pack that amounted to 511 W-hs per day! I'll talk about what the real power draw means to me and the car in a moment, but for now lets talk about the meter. The only problem is that I'm not so sure I can put it into words.
Essentially what we see is the meter failing to register the draw off the pack. Arguably, and presumably, if you increased the draw up to that magic 700 W-h per day error that seems to be inherent in the meter, the meter's reading wouldn't change much. For now, we can only speculate that would be true. What would be interesting to see would be if you increased the real draw on the batteries up to 800 W-hs per day. Would the meter begin to register that and show the real number? It's interesting to speculate, but I have no idea for now.
So what does the 511 W-hs per day that the DC to DC converters draw mean to me and the car? First, I'd like to know how much of that we can attribute to the fans. I can't easily get to the fans to see what their labels say with regards to power draw, but they seem to be ordinary 80 mm 12 VDC computer fans. One that I have laying around here says it uses .075 amps at 12 VDC. If we use those numbers (which are close enough for now), keeping in mind we have two fans, that comes out to a total of 43 W-hs per day. That seems like a pretty small fraction of the 511 W-hs that is actually being consumed. I can only assume that the remaining 468 W-hs is being gobbled up by the DC to DC converters as some sort of offering to the gods of inefficiency in the form of heat.
I think what that means is that it really would be worth while to look at turning the DC to DC converters off when the car is off. You may remember that I looked into that a couple months ago, installing a couple relays to turn the converters off when the car was off, and I ended up welding the relays shut. I contacted Ryan Bohm at EV Source and told him my dilemma. He recommended an "inrush limiter" for each of the converters. I ordered them and have them here. They really should be installed in the unit itself. Only downside there is that I have to take the converters out of the car to do so. Another task to add to the list of things to do. Mean while, the car still runs great and remains fun to drive.
On prior tests, the meter showed that the pack had lost 2.15 kW-hs, only to find when I charged the pack it would only accept around 200 W-hs. When I've worked out the math each time, I found that the Link-10 was introducing a about a 700 W-h per day error. If you want to be precise, it's actually 650 W-hs, but I rounded up 700 because it's easier for me to remember and for a few other reasons that would simply put you to sleep if I enumerated them.
Anyway, this time proved to be a bit different. I plugged in the car, started up the charger and stood there waiting for the charger to indicate it was done. I figured it would take 5, 10 minutes max. Well, after waiting for 15 minutes, and watching over a 1 kW-h be pushed to the pack, I realized that this wasn't going the way I'd expected. By the time the charger finally kicked off, it had pushed a total of 1.53 kW-hs into the battery.
Even though the Link-10 showed nearly the same draw over the 3 day test as it did on every other test, there had actually been a real draw off the pack that amounted to 511 W-hs per day! I'll talk about what the real power draw means to me and the car in a moment, but for now lets talk about the meter. The only problem is that I'm not so sure I can put it into words.
Essentially what we see is the meter failing to register the draw off the pack. Arguably, and presumably, if you increased the draw up to that magic 700 W-h per day error that seems to be inherent in the meter, the meter's reading wouldn't change much. For now, we can only speculate that would be true. What would be interesting to see would be if you increased the real draw on the batteries up to 800 W-hs per day. Would the meter begin to register that and show the real number? It's interesting to speculate, but I have no idea for now.
So what does the 511 W-hs per day that the DC to DC converters draw mean to me and the car? First, I'd like to know how much of that we can attribute to the fans. I can't easily get to the fans to see what their labels say with regards to power draw, but they seem to be ordinary 80 mm 12 VDC computer fans. One that I have laying around here says it uses .075 amps at 12 VDC. If we use those numbers (which are close enough for now), keeping in mind we have two fans, that comes out to a total of 43 W-hs per day. That seems like a pretty small fraction of the 511 W-hs that is actually being consumed. I can only assume that the remaining 468 W-hs is being gobbled up by the DC to DC converters as some sort of offering to the gods of inefficiency in the form of heat.
I think what that means is that it really would be worth while to look at turning the DC to DC converters off when the car is off. You may remember that I looked into that a couple months ago, installing a couple relays to turn the converters off when the car was off, and I ended up welding the relays shut. I contacted Ryan Bohm at EV Source and told him my dilemma. He recommended an "inrush limiter" for each of the converters. I ordered them and have them here. They really should be installed in the unit itself. Only downside there is that I have to take the converters out of the car to do so. Another task to add to the list of things to do. Mean while, the car still runs great and remains fun to drive.
Friday, August 6, 2010
A Quick Recap and A Few New Objectives
We're back from vacation and feeling great. Northern Arizona is beautiful country.
For those of you following along, you know I've been trying to sort out some apparent drain on the high voltage battery pack when the car is off. To do so, I've decided to test each, individual component, adding them one at a time to the system to see if I could determine the culprit.
What I was seeing, before the motor problems, was that when the car was sitting in the garage, off (or anywhere else for that matter), the Link-10 meter would report that approximately 1 kWh per day was being drawn off the pack. Through careful testing, I've discovered that the Link-10 is responsible for about 700 W/hours of that. That leaves about 300 W/hours yet to find. I say "about" because I didn't track the drain that carefully. It's just my recollection that it was about 1 kWh.
Anyway I've tested all the components, except for one, and found each draws no measurable power from the pack. Even the Link-10. It reports 700 W/hours per day, but it doesn't really use anywhere close to that. The only thing left to check is the DC to DC converters. Well, until summer ends, and the thermostat in the converters is happier with the air temperature, any test is not going to duplicate what I saw back in February and March. But I guess that's not entirely bad.
I've decided I'll go ahead and run the test with the DC to DC converters hooked up and running, even though the cooling fans will be spinning constantly the whole time. I'll still get some data, and it could be useful. I'll keep you posted on that.
By-in-large though, I think I've got most of what I was looking for. I know that the apparent draw off the battery pack, when the car is off, is a phantom. It doesn't exist. I wish the inaccuracy weren't there, but it is.
Now, there are still a few things that I need to do to the car. Some more important than others. I thought I'd share them with you now.
For those of you following along, you know I've been trying to sort out some apparent drain on the high voltage battery pack when the car is off. To do so, I've decided to test each, individual component, adding them one at a time to the system to see if I could determine the culprit.
What I was seeing, before the motor problems, was that when the car was sitting in the garage, off (or anywhere else for that matter), the Link-10 meter would report that approximately 1 kWh per day was being drawn off the pack. Through careful testing, I've discovered that the Link-10 is responsible for about 700 W/hours of that. That leaves about 300 W/hours yet to find. I say "about" because I didn't track the drain that carefully. It's just my recollection that it was about 1 kWh.
Anyway I've tested all the components, except for one, and found each draws no measurable power from the pack. Even the Link-10. It reports 700 W/hours per day, but it doesn't really use anywhere close to that. The only thing left to check is the DC to DC converters. Well, until summer ends, and the thermostat in the converters is happier with the air temperature, any test is not going to duplicate what I saw back in February and March. But I guess that's not entirely bad.
I've decided I'll go ahead and run the test with the DC to DC converters hooked up and running, even though the cooling fans will be spinning constantly the whole time. I'll still get some data, and it could be useful. I'll keep you posted on that.
By-in-large though, I think I've got most of what I was looking for. I know that the apparent draw off the battery pack, when the car is off, is a phantom. It doesn't exist. I wish the inaccuracy weren't there, but it is.
Now, there are still a few things that I need to do to the car. Some more important than others. I thought I'd share them with you now.
- Get the front end ride height adjusted.
- Get the front end aligned to remove any toe-in.
- Replace the differential fluid with Red Line (I did the transmission during the main build).
- Add an expansion chamber for the Zilla's coolant. You read that right. I didn't put one in when I was building the car. I realize now that wasn't the smartest thing, so feel free to mock me.
- Fit and adjust the v-belt for the compressor.
- Remove the AC lines and have them redone.
- Install a rubber membrane to the underside of the hood (bonnet, for my European friends) to keep the battery terminals off the steel in case of an accident. Let's hope that turns out to be a complete waste of time.
Tuesday, July 27, 2010
Getting Closer
This weekend's test with the Zilla attached proved to be as uninteresting as I had anticipated. The Zilla supposedly only draws 30 milliamps. What I found supports that. After three days with the Link-10, heater, charger, and finally the Zilla attached, the meter reported that 2.15 kWh's had been drained from the batteries. No different than any of the previous tests.
That leaves only the DC to DC converters left to test. As I've reported before, the ambient temperature here in Phoenix is high enough that the cooling fans on the converters run non-stop. I don't see any point in testing how much that draws off the pack. I'm far more interested in what is drawing power off the pack when the car appears to be doing absolutely nothing. But from the looks of things, that won't be the case until September some time.
For now I know that at least 700 of the Watt hours per day that the meter reports having left the pack is fictitious. I can live with that for now. I still have some other issues to deal with, which are minor in nature, but some of you may find interesting. Right now, I'm in lovely Sedona, so those will have to wait for next week.
That leaves only the DC to DC converters left to test. As I've reported before, the ambient temperature here in Phoenix is high enough that the cooling fans on the converters run non-stop. I don't see any point in testing how much that draws off the pack. I'm far more interested in what is drawing power off the pack when the car appears to be doing absolutely nothing. But from the looks of things, that won't be the case until September some time.
For now I know that at least 700 of the Watt hours per day that the meter reports having left the pack is fictitious. I can live with that for now. I still have some other issues to deal with, which are minor in nature, but some of you may find interesting. Right now, I'm in lovely Sedona, so those will have to wait for next week.
Friday, July 23, 2010
Testing: Stranger Still
I've been trying to determine which component is responsible for leeching power from the high voltage system when the car is idle. So far I've found that the Link-10 meter will unfailingly show a 700 Watt/hour per day loss, which I've determined to be largely inaccurate. I've run the same test with the ceramic heater hooked to the system (mind you it was off, just like the rest of the car) and it added nothing to the reported draw off the pack.
I finished a three day test yesterday in which I'd added the Manzanita Micro charger into the mix. At the end of the three day test I looked at meter, and what I found didn't surprise me at all. The meter read that there had been 2.15 kWhs drawn from the pack. That lines up exactly with what I would have expected, and so I can infer that the charger didn't draw any additional energy from the batteries. Again, not to surprising, but I have to test everything if I'm going to be thorough.
What was surprising is what happened when I charged the pack. In the first two tests, I saw that 2.15 kWhs had been drawn off the pack (according to the Link-10). But when I charged it, the charger read the pack as fully charged within minutes and when it finally shut off, it had only added 200 Watt/hours to the pack. So really, there was only 65 Watt/hours per day that were actually consumed. The first two tests had nearly identical numbers. Well, when I charged the batteries this time, the charger said the battery pack reached it's target voltage while I was turning the dial up to increase the current. When it finally kicked off, it had replaced a mere 60 Watt/hours. So, in this test, with only the Link-10, ceramic heater, and charger hooked to the high voltage system, their combined draw was 20 Watt/hours per day.
How could there be such a discrepancy? And how could the three components combined draw less energy than two of them? I think the answer is they didn't really. In spite of the fact that I'm trying to run these tests in the most controlled manner possible, I'm limited by the quality of the equipment. After all, it's not high dollar lab equipment, they're EV components. There is some inaccuracies inherent in each, i.e. the consistent 700 Watt/hour per day error in the Link-10. In this situation, I think we've exposed another inaccuracy in a different component, the charger.
The Manzanita Micro charger is fantastic as a bulk battery charger, and I think it does a terrific job. It is not a high dollar piece of bench lab testing equipment. It uses a potentiometer adjustment, made by the user, to determine the cutoff voltage for charging. I've set it such that the charger starts it's ramp down when the battery pack gets to ~165 VDC. It then ramps up to ~168 VDC before the timer runs out and it turns off completely. Now, the reason I use a "~ " is because it is it's all relatively approximate. Sometimes the timer comes on at 165 VDC, sometimes it comes on at 165.5 VDC. In addition, you may remember I'd said the algorithm it uses for how to ramp the current down is a complete and total mystery. So sometimes it will dump an additional 150 Watt/hours into the pack after the timer starts and sometimes (apparently) as little as 20 Watt/hours.
I guess the short of it is that using the charger as an instrument for doing the fine measurements I'd like to employ on this test is silly. At best I think I can only hope to get an idea of what's drawing current off the pack when the car is off. I've already discovered that the meter is responsible for most of what I've seen simply due to the error inherent within the meter. Am I going to find where that remaining 300 Watt/hours per day are going? I'm not sure, but I'm going to keep trying, and my feeling is that I'll find the DC to DC converters are drawing some of that current.
In any case, the next component to check is the Zilla controller. How much does it draw? Well it's supposed to be just a few milliamps. Over a 24 hour period, I'd be surprised if that registers on the meter. But I intend to test it anyway. That test began 30 minutes ago.
Stay tuned for the increasingly irrelevant conclusion!
I finished a three day test yesterday in which I'd added the Manzanita Micro charger into the mix. At the end of the three day test I looked at meter, and what I found didn't surprise me at all. The meter read that there had been 2.15 kWhs drawn from the pack. That lines up exactly with what I would have expected, and so I can infer that the charger didn't draw any additional energy from the batteries. Again, not to surprising, but I have to test everything if I'm going to be thorough.
What was surprising is what happened when I charged the pack. In the first two tests, I saw that 2.15 kWhs had been drawn off the pack (according to the Link-10). But when I charged it, the charger read the pack as fully charged within minutes and when it finally shut off, it had only added 200 Watt/hours to the pack. So really, there was only 65 Watt/hours per day that were actually consumed. The first two tests had nearly identical numbers. Well, when I charged the batteries this time, the charger said the battery pack reached it's target voltage while I was turning the dial up to increase the current. When it finally kicked off, it had replaced a mere 60 Watt/hours. So, in this test, with only the Link-10, ceramic heater, and charger hooked to the high voltage system, their combined draw was 20 Watt/hours per day.
How could there be such a discrepancy? And how could the three components combined draw less energy than two of them? I think the answer is they didn't really. In spite of the fact that I'm trying to run these tests in the most controlled manner possible, I'm limited by the quality of the equipment. After all, it's not high dollar lab equipment, they're EV components. There is some inaccuracies inherent in each, i.e. the consistent 700 Watt/hour per day error in the Link-10. In this situation, I think we've exposed another inaccuracy in a different component, the charger.
The Manzanita Micro charger is fantastic as a bulk battery charger, and I think it does a terrific job. It is not a high dollar piece of bench lab testing equipment. It uses a potentiometer adjustment, made by the user, to determine the cutoff voltage for charging. I've set it such that the charger starts it's ramp down when the battery pack gets to ~165 VDC. It then ramps up to ~168 VDC before the timer runs out and it turns off completely. Now, the reason I use a "~ " is because it is it's all relatively approximate. Sometimes the timer comes on at 165 VDC, sometimes it comes on at 165.5 VDC. In addition, you may remember I'd said the algorithm it uses for how to ramp the current down is a complete and total mystery. So sometimes it will dump an additional 150 Watt/hours into the pack after the timer starts and sometimes (apparently) as little as 20 Watt/hours.
I guess the short of it is that using the charger as an instrument for doing the fine measurements I'd like to employ on this test is silly. At best I think I can only hope to get an idea of what's drawing current off the pack when the car is off. I've already discovered that the meter is responsible for most of what I've seen simply due to the error inherent within the meter. Am I going to find where that remaining 300 Watt/hours per day are going? I'm not sure, but I'm going to keep trying, and my feeling is that I'll find the DC to DC converters are drawing some of that current.
In any case, the next component to check is the Zilla controller. How much does it draw? Well it's supposed to be just a few milliamps. Over a 24 hour period, I'd be surprised if that registers on the meter. But I intend to test it anyway. That test began 30 minutes ago.
Stay tuned for the increasingly irrelevant conclusion!
Monday, July 19, 2010
Testing Continued
Before I talk about the results of the most recent tests, I thought everyone might enjoy seeing one of the shots I took of the car, which I sent off for the book the EV Z3 is going to be in. Behold:
Considering the day was a bit cloudy and I don't own any lighting equipment other than a camera mounted flash, which I didn't use, I thought this turned out pretty good. Say what you want about the conversion, but it is a pretty car.
Anyway, back to the test results. So, over the weekend, I left the car idle, in the garage with only the following items attached to the high voltage side: the Link-10 meter, and the ceramic heater. As I mentioned in the last post, there is really no way for the heater to draw any current, but I swore I'd do more thorough tests, and that's what I intend to do. In fact, I decided against the idea of cutting that test short because I didn't expect the addition of the ceramic heater to amount to any difference. After all, if you allow your expectations to influence the method of your testing, your expectations influence and then determine the results of your test.
What did I find, you ask? Pretty much what I expected. The addition of the heater didn't change results at all. Over the time frame, the meter showed that 2.15 kWhs had been consumed. That is bang on what it said when I had only the meter attached. But if you remember back to that test, when I charged the batteries, they only accepted 200 Watt/hours. And after all, that's really what I need to know; how much energy was actually drawn out of the pack. This time was no different. About 3 minutes after I turned on the charger, the battery pack reached it's peak charging voltage and the charger began to ramp down.
By the time it had finished, 220 Watt/hours had been pushed back into the pack. I'm not concerned with that extra 20 Watt/hours that showed up in this test versus the first test. If I did the same test 10 times I'd expect 10 slightly different results because the charger introduces some randomness to the equation. The algorithm it uses to determine how many amps to push out while it ramps back down to zero during the cool down phase is anything but predictable. A 10% difference at this level is not a big deal. Considering the 2.15 kWhs the meter originally stated had been drawn off the pack, that 20 Watt/hours is only about 1%.
On the surface it would appear that I didn't learn anything. But really I did learn that the ceramic heater is definitely not drawing any current when it's off. It's true I expected that, but I also learned that the Link-10 showed the same error in metering 2 tests in a row.
In order to charge the battery pack I had to hook up the charger. That means that right now the Link-10, the ceramic heater and the charger are the only things hooked to the high voltage side. That sounds like a perfect recipe for the next test, which commenced 30 minutes ago.
Considering the day was a bit cloudy and I don't own any lighting equipment other than a camera mounted flash, which I didn't use, I thought this turned out pretty good. Say what you want about the conversion, but it is a pretty car.
Anyway, back to the test results. So, over the weekend, I left the car idle, in the garage with only the following items attached to the high voltage side: the Link-10 meter, and the ceramic heater. As I mentioned in the last post, there is really no way for the heater to draw any current, but I swore I'd do more thorough tests, and that's what I intend to do. In fact, I decided against the idea of cutting that test short because I didn't expect the addition of the ceramic heater to amount to any difference. After all, if you allow your expectations to influence the method of your testing, your expectations influence and then determine the results of your test.
What did I find, you ask? Pretty much what I expected. The addition of the heater didn't change results at all. Over the time frame, the meter showed that 2.15 kWhs had been consumed. That is bang on what it said when I had only the meter attached. But if you remember back to that test, when I charged the batteries, they only accepted 200 Watt/hours. And after all, that's really what I need to know; how much energy was actually drawn out of the pack. This time was no different. About 3 minutes after I turned on the charger, the battery pack reached it's peak charging voltage and the charger began to ramp down.
By the time it had finished, 220 Watt/hours had been pushed back into the pack. I'm not concerned with that extra 20 Watt/hours that showed up in this test versus the first test. If I did the same test 10 times I'd expect 10 slightly different results because the charger introduces some randomness to the equation. The algorithm it uses to determine how many amps to push out while it ramps back down to zero during the cool down phase is anything but predictable. A 10% difference at this level is not a big deal. Considering the 2.15 kWhs the meter originally stated had been drawn off the pack, that 20 Watt/hours is only about 1%.
On the surface it would appear that I didn't learn anything. But really I did learn that the ceramic heater is definitely not drawing any current when it's off. It's true I expected that, but I also learned that the Link-10 showed the same error in metering 2 tests in a row.
In order to charge the battery pack I had to hook up the charger. That means that right now the Link-10, the ceramic heater and the charger are the only things hooked to the high voltage side. That sounds like a perfect recipe for the next test, which commenced 30 minutes ago.
Friday, July 16, 2010
Not Much to Report
Everything has been running smoothly this past week. The few times I took the car out, it hummed along effortlessly, with no hint of a problem. For those of you not following Arizona's weather closely, it's been hot. Hotter than usual. Yesterday was 116 °F with humidity near 50%. There was no way I was taking the car out in that weather. Remember, no AC.
I'm continuing my tests this weekend to see if I can find which component is leeching power from the batteries when the car is off. So far the only configuration I've tested was to have the Link-10 meter hooked up by itself. You may remember that it reported 700 Watt/hours being drawn off in a 24 hour period.
The Link-10 will remain hooked up the entire time, after all, I need to monitor the pack during the test. But based on the previous test, we know the Link-10 brings along a 700 Watt/hour per day draw to the test. So I expect that if a component is drawing current, I should see more than a 700 Watt/hour per day reading on the meter.
Well, it's time to hook up the next item, and I need to choose which one. I still have to test the Zilla controller, the heating element, the charger and the DC to DC converters. Since the DC to DC converters have been fooled by the hot weather into thinking that they are too hot, their fans run constantly. So I think it's best I skip testing them for now. I think I'll move next to the heater.
Now the ceramic heater draws it's power directly off the traction pack, but it's behind two relays and a manual switch. In other words, in order for it to get any power, the car's HVAC fan has to be on, triggering the first relay. That makes the switch on the dash live. That switch must then be activated in order to trigger the final relay that actually sends power to the ceramic heater. So what are the chances that the heater is drawing any current when the car is idle? I'd say 0%, but I set out to test this methodically, and that's what I'm going to do.
I may not give the heater the full weekend to test it. If I see no change from the 700 Watt/hours I expect from the Link-10 in the first 24 hours, I'll add the next component and start the next test.
I'm continuing my tests this weekend to see if I can find which component is leeching power from the batteries when the car is off. So far the only configuration I've tested was to have the Link-10 meter hooked up by itself. You may remember that it reported 700 Watt/hours being drawn off in a 24 hour period.
The Link-10 will remain hooked up the entire time, after all, I need to monitor the pack during the test. But based on the previous test, we know the Link-10 brings along a 700 Watt/hour per day draw to the test. So I expect that if a component is drawing current, I should see more than a 700 Watt/hour per day reading on the meter.
Well, it's time to hook up the next item, and I need to choose which one. I still have to test the Zilla controller, the heating element, the charger and the DC to DC converters. Since the DC to DC converters have been fooled by the hot weather into thinking that they are too hot, their fans run constantly. So I think it's best I skip testing them for now. I think I'll move next to the heater.
Now the ceramic heater draws it's power directly off the traction pack, but it's behind two relays and a manual switch. In other words, in order for it to get any power, the car's HVAC fan has to be on, triggering the first relay. That makes the switch on the dash live. That switch must then be activated in order to trigger the final relay that actually sends power to the ceramic heater. So what are the chances that the heater is drawing any current when the car is idle? I'd say 0%, but I set out to test this methodically, and that's what I'm going to do.
I may not give the heater the full weekend to test it. If I see no change from the 700 Watt/hours I expect from the Link-10 in the first 24 hours, I'll add the next component and start the next test.
Sunday, July 11, 2010
Didn't Make it to Laguna Seca
Well, the REFUEL event at Laguna Seca went off today, and sadly I could not get there to participate. Over the last couple months, I reinstalled the motor and redid the front battery racks, getting the car fit and ready to participate. Where it all fell apart was in trying to arrange transport to get the EV Z3 to the track to participate. I don't own the right equipment and the cost of renting it was just not in the budget.
I'm hoping that there will be similar events here in Arizona in the future, but I'll just have to wait and see. I'd really love to get the car out on a track to see how it does.
On a better note, I took the car out for an extended drive early yesterday and found some interesting numbers. While here in the neighborhood, the car averages about 350 Watt/hours per mile (dismal). However, when out of the neighborhood, on surface streets, it averages about 250 Watt/hours per mile (better). The only thing that I can figure is the constant stopping and starting required by the high number of stop signs in the neighborhood take their toll quickly.
I believe the numbers can be better though. The transmission already has Redline transmission fluid in it, which reduces friction in the drive line. After I sent the transmission away to have the adaptor plate made, I filled it with Redline. I haven't yet put Redline in the differential, so I still need to do that. I don't know how much difference it will make, but it can't hurt. I'm keeping the tires at 45 PSI. The tire's maximum pressure is 51 PSI, so I'm well below the threshold, but they are certainly more firm than the normal 32 PSI.
There are two big things I need to do yet to help with efficiency. First I have to get the front end re-sprung. That won't affect the drive line, but it will get the ride height to the correct level. Once that is done, then I can have the front end aligned and take out any toe-in that's there now. I expect that will make the biggest difference of all.
So, why haven't I had the front end re-sprung yet? A couple reasons really. First, I had to take the car apart recently, you may remember. That hampered my ability to drive it anywhere. Second, the shop that can do it is in the middle of Phoenix, about 23 miles away. Now, the distance isn't a problem for the car, it can do 60 miles. However, the heat is a problem. It's been over a 110 °F lately, which makes for miserable driving when you don't have AC. Second, the little radiator and associated fans used to cool the Zilla have a difficult time keeping it cool in such high temperatures. I could drive the car there early in the morning, but by the time the car was done, I'd have to limp back home in the heat, doing my best to protect the Zilla. At this point, I'm inclined to wait until cooler weather comes so that I can get it there without any risk to the controller. After all, the car works great now, it just uses a bit more energy than I think it needs to.
Oh, and did I mention how much I love that new vacuum pump?
I'm hoping that there will be similar events here in Arizona in the future, but I'll just have to wait and see. I'd really love to get the car out on a track to see how it does.
On a better note, I took the car out for an extended drive early yesterday and found some interesting numbers. While here in the neighborhood, the car averages about 350 Watt/hours per mile (dismal). However, when out of the neighborhood, on surface streets, it averages about 250 Watt/hours per mile (better). The only thing that I can figure is the constant stopping and starting required by the high number of stop signs in the neighborhood take their toll quickly.
I believe the numbers can be better though. The transmission already has Redline transmission fluid in it, which reduces friction in the drive line. After I sent the transmission away to have the adaptor plate made, I filled it with Redline. I haven't yet put Redline in the differential, so I still need to do that. I don't know how much difference it will make, but it can't hurt. I'm keeping the tires at 45 PSI. The tire's maximum pressure is 51 PSI, so I'm well below the threshold, but they are certainly more firm than the normal 32 PSI.
There are two big things I need to do yet to help with efficiency. First I have to get the front end re-sprung. That won't affect the drive line, but it will get the ride height to the correct level. Once that is done, then I can have the front end aligned and take out any toe-in that's there now. I expect that will make the biggest difference of all.
So, why haven't I had the front end re-sprung yet? A couple reasons really. First, I had to take the car apart recently, you may remember. That hampered my ability to drive it anywhere. Second, the shop that can do it is in the middle of Phoenix, about 23 miles away. Now, the distance isn't a problem for the car, it can do 60 miles. However, the heat is a problem. It's been over a 110 °F lately, which makes for miserable driving when you don't have AC. Second, the little radiator and associated fans used to cool the Zilla have a difficult time keeping it cool in such high temperatures. I could drive the car there early in the morning, but by the time the car was done, I'd have to limp back home in the heat, doing my best to protect the Zilla. At this point, I'm inclined to wait until cooler weather comes so that I can get it there without any risk to the controller. After all, the car works great now, it just uses a bit more energy than I think it needs to.
Oh, and did I mention how much I love that new vacuum pump?
Friday, July 9, 2010
Stranger Still
Let me say that the following series of events falls outside my official testing scheme. Circumstances this week have kept me from continuing along the "add one item at a time to the high voltage system" plan that I want to follow. That said, I find the following thing puzzling and not all together irrelevant.
Tuesday, I had to hook all the connections back up to the high voltage side so I could back the car out of the garage. It then sat idle, with the DC to DC converter fans running the entire time until last night. I took it for a ride and used up 1.7 kWhs. This morning, the meter read that the systems had drawn a total of 2.9 kWhs from the pack. I charged the car, and watched carefully to see how much energy the Link-10 reported going back into the pack.
If it behaved anything like last time, it would have counted back from 2.9 kWhs to around 1 kWh and then the pack would have reached it's peak voltage and the charger would start it's 10 minute decline to 0 current. However, this time it got to 0.0 (meaning the meter thought the charger had replaced all the current that had been used) and continued on. It reached +.02 or 20 W/hours before the charger reached it's voltage limit.
When it was all said and done, the charger had dumped approximately 3.4 kWhs into the pack. That means that the Link-10 had missed 600 W/hours in it's metering duties since it was last charged.
To recap, the last controlled event the meter showed that 2.5 kWhs had been drawn off when it was really closer to 200 W/hours. This time it showed that 2.9 kWhs had been drawn off when it was really closer to 3.4 kWhs. Like I said before, this doesn't fit into my official testing plan, but I think it is significant. It's showing me that the Link-10 is really giving me an approximation of the current drawn off the pack at best. More to follow.
On the bright side, the car is running beautifully. Although I'm hearing an annoying rattle that I have to chase down.
Tuesday, I had to hook all the connections back up to the high voltage side so I could back the car out of the garage. It then sat idle, with the DC to DC converter fans running the entire time until last night. I took it for a ride and used up 1.7 kWhs. This morning, the meter read that the systems had drawn a total of 2.9 kWhs from the pack. I charged the car, and watched carefully to see how much energy the Link-10 reported going back into the pack.
If it behaved anything like last time, it would have counted back from 2.9 kWhs to around 1 kWh and then the pack would have reached it's peak voltage and the charger would start it's 10 minute decline to 0 current. However, this time it got to 0.0 (meaning the meter thought the charger had replaced all the current that had been used) and continued on. It reached +.02 or 20 W/hours before the charger reached it's voltage limit.
When it was all said and done, the charger had dumped approximately 3.4 kWhs into the pack. That means that the Link-10 had missed 600 W/hours in it's metering duties since it was last charged.
To recap, the last controlled event the meter showed that 2.5 kWhs had been drawn off when it was really closer to 200 W/hours. This time it showed that 2.9 kWhs had been drawn off when it was really closer to 3.4 kWhs. Like I said before, this doesn't fit into my official testing plan, but I think it is significant. It's showing me that the Link-10 is really giving me an approximation of the current drawn off the pack at best. More to follow.
On the bright side, the car is running beautifully. Although I'm hearing an annoying rattle that I have to chase down.
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