Wednesday, March 2, 2011

The Z3's One Year Anniversary

It was one year ago today that the Z3 rolled out of the garage for the first time as an EV.  Since that day a lot has transpired.  Some of what I've learned you may find interesting or perhaps even useful in your own EV adventures.  With that in mind it seems only appropriate that I take some time here to recap what the first year of driving the EV Z3 has been like and discuss what I've learned as a result.  So grab a refreshing beverage, perhaps a light snack, kick back and enjoy the read.

Technical Issues, good and bad:

From the first tests of the car, I found that the car was much slower than expected.  Zero to 40 was 20 seconds or more, and 60 mph was a distant dream.  It just didn't make any sense.  After all I had a 1000 amp controller and a WarP 11 motor!  I had set the controller to limit the current to only 500 amps at first, but I could see on the Link 10 meter that it never seemed to draw more than 250 amps.  I gathered data from the Zilla's output and ultimately forwarded it off to the experts, only to find I'd made a relatively common mistake.  I'd set the low voltage battery indicator (LVBI) parameter too high.

Interested in protecting the batteries from being discharged too far, I'd set that parameter to 140 Volts, which is just under 3.0 Volts per cell.  I had no idea that the battery pack's voltage would sag below that under the first real load.  The whole thing would happen so fast.  I'd press on the accelerator, the voltage would drop, the Zilla would cut back, all within a second or two, so I never even experienced what full throttle felt like. The Link 10 didn't even have the time to display the low voltage before the Zilla would cut the current back and the voltage would recover, so it remained a mystery to me. 

Once I was set straight and advised to set the LBVI closer to 110 volts, the car behaved more like I would have expected.  But not quite.  Zero to 40 is now somewhere around 5 seconds with the car hitting 60 mph in 11.5 seconds.  That's not as fast as I would have liked but absolutely tolerable.  I still wasn't sure why that was the case, but I discovered why in due time.  Being new to this entire endeavor, I had no idea how to size a battery pack, nor how a batterie's "C" ratings can affect you in the real world.  As it turns out these CALB cells can sustain a 3C output.  I have 120 amp/hour cells, which means that they can only put out 480 amps sustained.  That means the Zilla never really puts out the 1000 amps it's capable of.  Ok, it might for a second or less, enough time to spin the tires for a moment, but no more, I assure you. 

If I had the chance to do it all over again, I'd choose the 200 amp/hour cells and figure out someway of fitting them in the car.  That would get me a sustained output of 800 amps, a much more attractive number.  However, until such time as I receive a hefty windfall of cash, I'll be keeping the 120s.

After all that was sorted out, I had roughly 1.5 months of trouble free driving.  But toward the end of April, I noticed a vibration in the drive line.  On April 29th I had to put the car back in the garage and remove the motor and transmission.  I ended up finding that the motor had come out of balance in what was described by George Hamstra of Netgain motors, as a very unusual situation.  The balancing putty had come off the armature.  Like a hero to the rescue, George had me ship the motor back and they fixed it up as good as new in record time.  I decided to take the opportunity to redo the battery layout in the front.  That extended the down time to two months, so the car was not back on the road until June 30, the middle of summer.

As you might have guessed, the middle of summer is pretty hot here in Arizona.  Hot enough that driving a car without AC is down right unpleasant.  I still hadn't hooked up the AC compressor, so that meant no cold air.  Taking the top down isn't really an option because then it's still hot and the sun is hitting you.  But the bigger issue was that the Zilla controller began complaining that it was getting too hot.  The ambient temperature was close to 120 °F, and the Zilla's first thermal cutback is 131 °F.  As you might expect, it took almost no time at all for the Zilla to reach that.  It only cut the output to 75% at that temperature, but I was surprised how much of a difference that made.  But the larger issue is the potential for damage over time.  The cooler electrical components are, the longer their life, and the last thing I want to do is compromise the Zilla's health.  A larger radiator might help dissipate heat better, but realistically, I don't think I can hope to keep the controller under 131 °F in the middle of summer.

I'm afraid that isn't the only heat issue.  I've taken a few temperature readings of the batteries, starting when they'd been sitting over night and were at ambient temperature, and then reading them again after a 12 mile drive.  I did this a couple times this winter when we had some unusually cold weather, temperatures in the low 20's.  I was concerned the low temperature might affect the batteries performance, but I was pleased to find it didn't at all.  The car performed no differently than when it's 80°s outside. What I did find, however, was that the batteries rose between 15° and 20°s over the course of the trip.  Well, that could be a problem.

Imagine, if you will, that the weather report says it's 115 °F out.  I can tell you from experience that when they say it's 115° at the airport, it's over 120° on any given surface street around town.  That means in a relatively short period of time, the batteries are going to be at or above 120° just from having the air blow over them.  Couple that with the potential 20° rise in temperature from use, and they are now between 135 and 140°.  Well, 140° is the magic number for these batteries where the organic solvent used as an electrolyte starts to decompose.  Bad news if I'm trying to preserve the longevity of the batteries.  Now imagine that I've hooked up the AC compressor, and the excess heat thrown off from the condenser is flowing right over the batteries just behind it.  You may be recognizing the predicament I face.

It looks like normal daytime driving during the hottest days in the summer is perilous at best, with temperature risks to both the batteries and the controller.  Throw the AC system into the mix, adding more heat to the equation, and it becomes downright irresponsible.  Sadly, I think this all means that I'll have to eliminate driving during the hottest parts of the day in the summer.  Hopefully I can get away with some driving at night. But of course that means that there really is no point in hooking up the AC compressor either.

Once summer was over I started driving the car on a daily basis.  It has been completely trouble free.  I start it (or turn it one, would be a more accurate phrase) and then drive it.  No worries, and no troubles.  It's wonderful! 

In an effort to be straight with you, I've shared all the difficulties I've had and the ones I'm still facing.  The problem is that last paragraph, the one tiny one about how great the car is to drive, seems almost lost in comparison with the less than ideal information before it.  It's difficult for me to give that last paragraph the weight or emphasis it deserves.  The problems I've had pale in comparison to the joy I experience driving the car day to day.   The strong torque at start up, the smooth quiet acceleration, driving straight past gas stations, all these things add up to an experience that is hard to convey with words.  It's sublime, and it needs to be experienced to be fully appreciated. 

Community Engagement:

I've had the opportunity to take the car to two car shows, and it was well received at both.  There must have been around 100 people between the 2 shows that approached me to ask about it.  I've had about 8 visitors come by the house to look at it; 2 local people and 6 others that had come from out of town.  I've had a few people ask me about the car while I was driving in the neighborhood, or in local parking lots.  You may have read just last week that I took the car to ASU to show some engineering students.  The reactions are always the same; people love the car.  The questions are always the same, how far does it go, how long to charge it.  Everyone seems amazed to find that it is my daily driver.  The best thing about showing the car to people is that they start to see the possibility that an EV is a viable option.  You can always tell the ones that are the most skeptical of the technology.  To them I explain what I've always felt, and that is if a family or person has two cars, then the odds are that one of them could be electric and they would suffer no inconvenience in their lives.

Battery Report:

Here we are, one year after the car rolled out of the garage without a BMS and the batteries are fine and the car works just as it should.  I had people warn me that I needed to put a BMS on the batteries or they'd be ruined in no time at all.  Clearly not the case.

I did have the one scare back in September where I monkeyed with the charger and over charged a couple cells by a bit.  They may have been damaged, but so far they've shown no signs of damage.  I expect that years from now when the pack has 150,000 miles on it. they might be the first to show signs of decreased capacity.  But that incident was entirely self inflicted!  I recovered in short order, and learned a lot in the process.

Last month I bottom balanced the pack.  I checked the battery's voltages every time I charged them for the first couple weeks.  I found that the charger is cutting off when the highest battery in the pack is at 3.47 volts.  Well below the 3.6 volt ceiling that CALB recommends.  Even with that very cautious and conservative charging regime, the batteries are still holding 119.5 amp/hours.  I'm playing it safe, charging carefully and not over discharging the batteries and they are fine.  End of story.

Statistics and other Damned lies:

Our illustrious leaders often use statistics in questionable ways, slanting them as support for their agenda.  I'm going to see if I can avoid that.  I don't really have an agenda after all.

I keep a spreadsheet of every aspect of the car that you can imagine.  I'm not normally so obsessive about such things, but I figured if I was going to understand how cost effective, or in-effective this whole endeavor is, I needed accurate data.  So every time I charge the car, I make a note of the miles I've driven, and the amount of power I used.  It's yielded some very interesting information.  I've also kept data on each individual battery in the pack.  That has yielded absolutely nothing interesting.  Well to be fair, the fact that it contains nothing alarming is interesting, but it is the only interesting thing about that data.

Lets get to it.
4233 - Total miles I've driven.
1648 - Total kWh's I've used.
389  - Average number of Watts/hours per mile consumed.
192  - Total gallons of gas I didn't use.
$506 - Total amount of money I've saved using electricity vs. gas.
$0.03 - Mean average cost per mile.
20.4 - Mean average number of mile traveled per charge.
39.1% - Mean average depth of discharge.
39.6% - Median average depth of discharge (for all you statistics nerds). 
46.3 - Mode average depth of discharge (for all you hopeless statistics nerds).
212 - Number of charging cycles.

Here's a chart I put together which is just plot points showing every time I've discharged the batteries and to what depth of discharge (DOD) I took them.  Note that there is no declared value to the X axis on the chart, though it is actually date related with the far left being the first charge.  Also note the one point higher than 100%; that was when I took the pack down to near depleted so I could bottom balance the pack (it gave up 127.5 amp/hours or 105% of it's stated capacity).

I'm sure you'll notice a grouping around the 55% DOD level.  Those would be my drive to work.  Some notes on the data.  In the formula I've used to figure out the cost the electricity I've used, I'm factoring in 10% loss in the systems due to the normal inefficiencies of converting current.  That may be a bit heavy handed, but I'd rather err on the conservative side.  When I drove out of the garage last year, gas was at $2.75/gallon for premium (that's what the car required before the conversion).  Yesterday I drove by the Costco near my house to find out how much it is now: $3.49.  The funny thing is I had to walk up and ask because they don't have it posted on a sign.  I'm not buying gas very often these days.  The average Watt/hours per mile of 390 might seem kind of high, but that's because a good portion of the miles I've put on the car were done on the highway at 65 mph when the car averages about 410 Watt/hours per mile.  If I drive at 45 mph, the car gets closer to 320 Watts/hours per mile.

Oddly enough I got a very interesting and timely piece of mail today.  It was from my power company detailing my power consumption over the past year, comparing it to my power consumption the previous year.  Like I said, timely.  But as we're not talking about a controlled experiment, the numbers are only interesting, not indicative of a trend associated with the car coming online.  As it turns out, we used more electricity in 2009 than in 2010 during the period when the car was operating; 5 kilowatt/hours more to be precise.  But I had switched to a Time of Use plan when I started driving the car so I could take advantage of off peak power rates.  As a result, we saved over $72 this past year on our power bill compared to the previous year.  Interesting, but ultimately not really related to the car. It is noteworthy though because one of the arguments people use to dispute the advantages of EVs is they say your power bill will go up by a lot.  Hmm... that doesn't seem to be foregone conclusion does it?

Let's go for a ride:

I thought it might be nice to take the car for a short drive and film it so people can get a feeling for what the car's like.  Take a look.


The video quality is pretty poor, but at least you get an idea of what it's like to drive the car. 

Conclusion:

So the question is "Has it been worth it?"  From a project point of view, yes.  It was a terrific project and I enjoyed nearly every moment working on it (I did crush my finger badly and that wasn't much fun).  While I intended to build it in such a way that I wouldn't have to tinker with it after I was done, I find myself tinkering with it anyway because I enjoy working on it.  It's become an enjoyable hobby.

Has it provided me with reliable transportation?  Yes.  Like I said before, I turn it one and drive it, it's that simple.   Has range been an issue?  Three times in the last year while traveling in the city I've needed to go further than the car would take me, so I had to use my gasoline powered car.  The other three hundred plus trips I've made I used the EV.  So, has the 60 mile range been an issue?  Yes, less than 1% of the time, range has been an issue.  Not bad odds.

Do I experience range anxiety?  I did for the first couple months, but slowly realized that it just wasn't an issue.  It simply requires one more step before you leave the front door.  You get your wallet, phone, keys, sunglasses, do a quick sum of the distance you need to go if it's someplace you haven't already been, and then walk out the door satisfied that all is in order. I used to watch the amp meter like a hawk.  Now I just tend to look at it when I pull in the garage so I know how much power I used so that I can record it in my spreadsheet.

Did it make sense financially?  Not really.  Or perhaps I should say, not entirely.  If I were to go buy a Nissan Leaf, I'd pay roughly what I paid for this car.  I'd have a car with all the environmentals that one would want in a desert, plus a warranty!  But let's face it the Z3 is prettier.  I could have kept the ICE in the car and not spent the $23K to convert it.  You can buy a lot of gas for $23K.  However, slowly and surely, the car will save me money; $506 this year, and likely more this coming year judging from the rising prices of gas.  Will it pay for itself?  Will I make the money from the conversion back in gas savings?  I sure will.  If gas rises to $4.50 a gallon, I'll make the conversion cost back somewhere around the point I've put 135K miles on the car.  When you take into account the decrease in maintenance costs that comes down a bit, but you get my point.  You don't convert a car because it's going to save you money.  At least you don't convert a Z3 for that reason.

Everyone who's ridden in the car exclaims how much they love it.  Everyone who's driven the car, at some point and to some level, express how they now get it.  They understand why people who drive electric cars like them.  They leave thinking of the possibility of owning one themselves.  Will electric cars take the world by storm?  I'd like to think so, but I don't think they will.  It will be a slow, steady adoption.  But I'm certain that the people that go EV, will likely not go back.

Pat yourself on the back for making it through the longest post I've ever written.  I hope it was informative and interesting to read.  Thanks to all who've read the blog over the past couple of years and to those who've posted comments, questions and advice.  I'm glad to be a part of this community.

12 comments:

Rob said...

Very Nice! I really liked the video, and I need to do the same at some point. Sorry to hear you are not getting as much amp output as you had hoped. Getting that Z3 up to 600-700 Amps sustained would really make a great difference.

Have you tried dropping the Zilla low voltage cut off even more? I think I remember Jack Rickard at EVTV telling me that battery sag during load is no big deal. If it doesn't damage the pack, then maybe let it sag to say 1.8V per cell, or 86V for your pack, and get as much output as possible? I think the Zilla over estimates battery sag anyway. I monitor my cells during load, and I never see average voltages go below 2.3V even though I had my cut off at avg 1.8V/cell.

I guess one concern is if the LBVI is too low then your limp mode may not work soon enough to protect the batteries at end of discharge. You could then use the valet mode on the Zilla to switch for higher performance when you know the pack is mostly full.

I wonder what the newer CALBs performance is like. I heard they can do 10C continuous but haven't heard that verified. I need to look at Jack's speedster part Duh specs, because he used the CALBs. I think they were getting a 1000A to the Soliton1. Enjoy!

Tim Catellier said...

Hi Rob,

Thanks for commenting. You are absolutely right, 700 to 800 amps would be so nice in that little car. It would scream!

Sadly the 480 amp limit I'm seeing is simply a function of the physical or chemical limitations of these cells, not the Zilla cutting the current back. Ever since I made the adjustment to the LVBI parameter in the Zilla, it has never triggered, and truthfully that's just fine with me. My opinion is it's better to monitor the state of the batteries by watching the amp/hours used vs. the voltage of the pack. Plus using the controller's LVBI to manage the batteries and specifically relying on it to manage the amount of current the controller pulls from them is a bit like driving a nail with a sledge hammer. It'll work, but it's clumsy, prone to error and the wrong tool for the job.

I don't know how Jack has managed to get 1000 amps from his CALB 180 cells in the Porsche Re-dux. Theoretically they should only put out 760 amps sustained (4C or 4x180). All I can tell you is my 120s really will do only a 4C discharge. No matter how long I hold my foot to the floor, or how nicely I ask, 480 amps is the most the batteries will give me.

andy said...

Neat conversion. I want one. I live in Tucson and would have the same heat issue you do.

Nutty Ideas: If you had 17.7" x 9.4" x 15.0" (L x W x H) in the trunk and could properly mount/soundproof/exhaust a Honda EU1000i then .6 gal of gas would get you 120v 900W rated (7.5A) for 3.8 hrs (8.3 hrs. @ 1/4) load. Lotta MPG. Maybe that would drive the house electronics and a A/C compressor drive motor. The gen ramps up or down automatically when the Compressor cycles on or off. Probably need some sort of fluid chiller battery box and maybe heatsink/Peltier Thermoelectric Cooler (TEC) arrangement for the Zilla.

The gen weighs 29 lbs. and getting everything to work within the rated output of the gen would be a challenge I would think.

It might seem strange to pull start a gen in the trunk before you depart.

Hipo_EV said...

Hi Tim,

I'd think your missing performance is due to one of two things:
(1) thermal protection
(2) hairball setting

For (1), this can easily be checked by connecting the correct pin from the hairball to your check engine light.

Once the Zilla's heatsink temp goes over 55C, your CEL will blink/flash and your current will be limited to 75% of the value you have set. This is a possibility to your problem.

For (2), which is what I think is actually the problem, can you post the settings you have for the following parameters under "display settings":
Battery Menu
BA, LBV, LBVI
AMP, Volt, RA
RV, PA, PV
Norm, Rev, Max
Errors


I suspect that one of your settings is limiting you, either artificially or by mistake.

basically your cells will limit you for overal voltage and amps available anyhoo, so you should just set your motor amp and voltage limits higher to rule out artificial limits.

Also, your CALB cells should do 5C at 75%, so if you really wanted the most performance, you could test that out as well.

But just to point the main problem out, if you are being limited to 250A, and your pack voltage is approx 156v, your HP is going to be <52hp - not that much ;)

If you can work out why there is that 250A limit, then you can increase that horsepower dramatically - 4x that is possible :)

My suggestion, as stated earlier, is to set the values for the motor amp and voltage limits higher, so no artificial limits will come into play, and then use the battery limits to keep the CALB cells safe.

Try the follow:
Battery Menu
BA: 480-600 (4C or 5C)
LBV: 125 (2.6V lower limit)
LBVI: 134 (2.8V warning)

Motor Menu
Amp: 1000 (limit of controller)
Volt: 156 (your pack voltage)
RA: 0 (reverse option not needed)
RV: 0 (reverse option not needed)
PA: 0 (parallel option not needed)
PV: 0 (parallel option not needed)

If you immediately notice a difference, then you can start to adjust the AMP value to find a suitable balance between performance and range :)

Leslie

Tim Catellier said...

Leslie,

You're right, I did fall into that trap early on. An incorrect setting was my problem. I'd give it throttle and it would immediately go into limp mode and cut back. But now the Zilla's LVB limit is set for 100 V. The pack never sags that low under load. There's no cut back happening.

The motor amp limit is set to 1000, and so is the battery amp limit. So that is not the issue either. Nope, the issue is the batteries. Every spec sheet I've seen on the CALBs says they'll do 4C sustained, and they are not kidding. I have 120 amp/hour cells, and they put out 480 amps sustained. Sure, I will see a spike above 600 for an instant but then it falls right down to 500-480 in no time.

I do have the Zilla hooked up to my "Check Engine" light, which is how I knew it was overheating this last summer and going into thermal cutback. It would get hot, the light would begin to flash and the car's acceleration would be dismal. Under normal driving, in cool whether the Zilla remains nice and cool and never reaches 55 °C. No thermal cutback is going on either.

You're analysis is dead on accurate, and I experienced those issues and problems early on. But I've worked out those problems and run into the one I can do nothing about. At least not without swapping batteries.

Andy,

Lack of power to the accessories hasn't been a problem. So putting a generator in the trunk to power the AC compressor isn't going to get me anything. Apart from more heat in the trunk, which I don't want. At this point the real problem with AC is the extra heat it would spew across the batteries. If I could relocate the condenser, that would help, but to where? There's no room left!

Thanks for the comment though.

andy said...

I'm sure I don't quite understand the heat problem. Just curious, You have ruled out power cooling ie: Peltier TEC) and heatsinks to moderate the summer heat on the components?

My nutty idea was sort of a Chevy Volt notion.

Tim Catellier said...

Hi Andy,

There are only two components that face over heating issues in the summer; the Zilla and the batteries. Throwing some extra cooling capacity on the Zilla would likely solve it's overheating problems in the summer, and I'll likely do that; I have room for that. But by far the biggest cooling problem I face is with the batteries.

The batteries are constructed in such a way as to allow airflow between them. That does help cool them, but when the air blowing over them is already 120° or more, that air can only do so much. To be effective and prolong the life of every cell, I would need to sandwich a heat sink between every battery, and I'd need one that was big enough or efficient enough to suck at least an additional 10° of heat out of each cell. 15° would be better! Peltier, water cooling, or liquid nitrogen for that matter would do the job. I'm not saying it couldn't be done, but the issue becomes one of space. The components are crammed in there so tight that getting any extra heat sink or cooling apparatus between the cells would mean I'd have to take some of them out to make room.

Since adding and subtracting cells in the car on a regular basis is not an option, that means I'd have to remove the cells from the pack necessary to make space for the cooling, and leave them out for good. That translates to reduced range. Right now, that's not a choice I'm willing to make. This whole project has been about managing compromises. It seems every time I've turned around I had another decision to make where there was no one perfect choice. I'm not complaining though, it's just the way it is.

Hopefully that cleared things up.

andy said...

12v 30w thermoelectric cool/heat car seat cushion.

http://www.huimao.com/pad.htm

andy said...

I see. You say, "The batteries are constructed in such a way as to allow airflow between them." I'm looking at your photo of the blue bat boxes and it looks like the batteries are pretty much sealed in the boxes. I take it you don't have much if any room between the top of the bat boxes and the car hood?
Maybe Superterm paint to insulate the boxes? Looks very thin to me. http://www.youtube.com/watch?v=LtBICM4F1Gs

Just brainstorming...

andy said...

Not to be a nag but I still can't get over how nice your Z3 EV is. Your video's are well done I might add.

Thermal Battery Mng. interesting subject to say the least.

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/aabc_presentation.pdf

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/jte_2003-633_sw_ap.pdf

Tim Catellier said...

It's not a bother Andy, I appreciate your interest in the car. But as you can clearly see from the documents you referred to, cooling batteries is an important, complicated endeavor. One manufacturers take very seriously. The advantage manufacturers have is that they can design everything from scratch. They aren't constrained or limited to the space defined by a donor vehicle. I started with 'x' amount of space, and I can't really add any.

I'd love to find a practical, compact way of keeping the batteries cool in summer. I haven't given up. I just haven't found the solution yet.

andy said...

I've been watching these guys drag race electric cars and setting records with SLA hawker batteries. I'm thinking the race community will solve the heat problem to win races. Cold plates .3˝ thick in a plug'n'play battery box/mount design would be what I'd expect. 3.2v 300ah square modules in a thermo-electric cold plate matrix.

http://www.lytron.com/cold-plates/standard/cold-plates-CP15.aspx