Friday, December 31, 2010

What I've Learned This Year

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 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.

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.