Stroking Batteries in Hot Weather

In this myiMiEV Forum we have had many discussions about the care and feeding of our traction battery pack, with some of us favoring -

- Not fully charging unless a long trip is imminent
- Never fully discharging
- Keeping the battery around 7-8 bars if storing the car for an extended period of time

- And I'll add that if the battery capacity is low (three bars or below), not to draw high currents (i.e., keep the red needle in the green zone)… I would expect this to be a natural reaction if down that low anyway.

In this thread there was a discussion about the iMiEV's battery management system:
http://myimiev.com/forum/viewtopic.php?f=10&t=255
As mentioned in it, the battery pack uses the cabin air for its heating/cooling, and there also appears to be a cooling fan within the battery compartment itself.

After reading some of the disturbing symptoms on the myLeaf Forum which suggest possible hot-weather-related battery capacity degradation, I began to wonder how best to treat our iMiEV battery pack on a hot summer day. In addition to simply taking it easy on the go-pedal (thus minimizing high currents), the following crossed my mind -

1. Run our air conditioning on a hot day in order to provide battery cooling (I know it's counter-intuitive to use the battery power to cool itself).

2. After arriving home hot, immediately plug in the Level 1 charger and, using the Remote, turn on the air conditioning to keep the battery pack from languishing at high temperature

3. Especially in hot weather, time the charging to stop at no more than 14 bars

Does anyone think this would do any good… or is it simply a case of my paranoid "can't hurt, might help" overkill?

Being an early adopter and recognizing that the manufacturer probably doesn't have all the worst-case scenarios fully addressed yet, I'd like to give my batteries a fighting chance at longevity.

Edit 29 April 2013. I now think running the aircon and plugging in the car right after driving thinking it will cool the pack is not a good idea. See the 29 April 2013 post on this thread.

I've been trying to be nice to the batteries, not "topping off" unless I know I'll need the range the following day.

Regarding A/C ... it seems that you're implying running the cabin aircon will cool the battery pack, do you have some documentation of that, because I don't recall reading or hearing about that officially (I only see the one post FiddlerJohn made about it - and your question: Did Mitsubishi assume passenger temp is good for batteries? ... Without an answer).

I heard about the quick charge coming with the ability to cool the pack using the car's A/C - but I would have figured there is some type of automatic thermostat on the pack that would turn the AC on and direct flow from the A/C to the pack when necessary (at least during quick charging - I have no idea about other times). Because in some cases (very sunny days, but not too hot) you may run the A/C to cool you and your passengers but cooling your pack in those instances might be counter-productive.

As far as you being paranoid - well, despite this being a really fun car to drive, it is new technology and sometimes there are glitches, so staying withing a 40-80% SOC, keeping the batteries cool, and driving conservatively (I stomped on it the other day from a light up a hill - sure is fun - but feelt some kind of lag, wondering if it was the heat and the excessive current draw [I'll try not to do that again]) are all good ideas. Even if Mitsu covers it, going through the hassle of a breakdown or having some other issue on a vehicle is better avoided than trying to correct.

Yesterday it was 92F here, and I pulled the car into the garage for charging. I noticed that the battery pack fan ran longer than normal at first, but then stopped. I had to interrupt the charge mid-way (garage door repairman needed the car moved), and on starting the car, the battery fan ran continuously until I turned the car off. I'm guessing the pack was too warm from charging.

Once back in the garage, I waited a couple hours to restart the charging process. Just normal fan on/off at that point.

I'm hoping that Mitsubishi has sorted out some of the high temp issues on the battery pack and that is the reason my car's pack fan ran as it did yesterday.

JoeS said:

. . . . recognizing that the manufacturer probably doesn't have all the worst-case scenarios fully addressed yet, I'd like to give my batteries a fighting chance at longevity.

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I'm with you all the way Joe - We've already had several days north of 95 degrees here this summer, so of course this subject is of real interest to me. I just wish I was smart enough to know what to do . . . . or at least what not to do that might make the situation even worse. Happily I have discovered (using the car's thermometer) that it stays about 6 or 8 degrees cooler in my garage than the actual outdoor temps . . . . I think that may be because my garage is all brick and concrete and it has a very well insulated roof system

So far, I've elected to never put the car on the charger unless the pack is less than half full - I.E. it's always down to 7 bars or less. I also try to discharge it down to about 2 bars every so often . . . . every 3 or 4 weeks. Whenever practical, I use the Level 1 charger 100% of the time, only resorting to Level 2 on those very rare occasions when I'll need to use the car again before the Level 1 charger would have put enough back into the pack. 95% of the time, Level 1 will have it fully recharged overnight if I put it on the charger after the last use of the day. We use the A/C liberally down here in the south, but mainly because WE need it, not because I'm thinking about it being good for the battery pack. Will I remember to turn the A/C on in the winter when we're heavily loading the pack, like when driving on the Interstate? I kinda doubt it

What I'm not doing (so far) is partial charging. I haven't convinced myself that not topping it off all the way is better for it than getting the full charge - My (probably flawed) reasoning is that if it was good practice, Mitsu would have made it much easier to do. The car is basically a rolling computer and they've included so many high tech innovations, it just seems they would have given us the option to 85% or 90% charge if it was at all desirable to do so . . . . they have more at stake I think with possible future battery problems than the individual owners do - It would have been so easy to just program the charger to stop at any desired SOC so if it was at all beneficial for the battery. I gotta think that option would be there if that was the case

I'm interested to hear what everyone (Leaf and all other owners as well) thinks on this subject, and if it makes any sense to me, I'll be there with all of you - Nobody wants their battery to last longer than I do mine, and I'm already a bit more pessimistic about long term battery life than most people seem to be

Don

Seeing that several warm-climate LEAFs are already down to 85% of rated battery capacity at the one year checkup,
http://www.greencarreports.com/news/1077227_nissan-leaf-does-a-battery-inspection-give-peace-of-mind
I'm thankful to now live in the land of temperate drizzle (south of Seattle at a sunny 71 degrees ;-) .
That being said, I'm also of the mind that the more miles this car racks up, the better my use of capital and the most minimized my fuel cost will be (as well as carbon footprint and whatnot). Of course, I'm not talking about joyriding, just regular use, and there's nothing like owning a limited range EV in a rural area to encourage trip consolidation! So, I 'll charge 'er fully on most days, run it down into single digits sometimes, and stand ready to press the warranty issue if need be when the time comes. Meanwhile, I'm also comforted by the falling price of lithium cells and the high cost of gasoline.
6700 miles and counting...

I've also been reading up on Nissan Leaf forum and had couple of questions regarding our Miev:

Does our Miev use a similar BMS as the Leaf or is it a little more active in cooling the battery, you would think Mitsu having been developing this Miev before the Leaf was conceived had a few years headstart in developing their BMS?

Is there any way to measure our Miev battery temp, Leaf provides a battery temp gauge?

Is there a way to measure capacity loss on our Miev battery pack? Leaf provides a gauge next to battery SOC. Will we lose a SOC bar upon capacity loss? Aside from going into the dealership, any options for measuring?

Doesn't fully charging the pack rebalance the batteries? The "i" doesn't have a Long Battery Life charging option like the Leaf and judging when the pack is near 80% is kind of difficult unless I'm willing to check the guage every so often. I'm thinking that the battery range showing is taking in account the 80% desired charge level. Also, I think I read in the owner's manual to charge the pack to full capacity. I didn't see anything in there not to do so. I'm going with the manual on this one.

Even level 2 charging is only tiny percentage of the batteries' C rate while driving, about 10% IIRC, so I don't see how sticking with level 1 charging will make an appreciable difference. Why worry about such slow rates of charge especially if it can mean reducing the utility of the car? DIY high-speed recharge such as with an external charger going directly to the battery pack at 50 or 75 amps, now that might be something to think twice about...

Well, we know that it's a 16Kw pack and that it's 330 volts, so that gives us the C (capacity) of the pack at 48.5 AHrs - A 15 amp Level 2 charger puts power back at roughly 1/3 of C . . . . certainly nothing around 10%. True, it will supply up to 150 amps to the motor for brief periods, but I'm sure that discharging it at 3C isn't really good for it either. I'm guessing the fewer times you do that (and the fewer seconds you keep it up there) the longer it will last

We know the pack warms up some when charging with the 8 amp Level 1 charger because the battery cooling system cycles on regularly . . . . not nearly as often as it does when Level 2 charging, but even 8 amps @ 120 is enough to heat it up to some degree

Will the pack last longer if you only use Level 1 charging? I honestly don't know, but everything I've ever been taught over the past 40 years or so about recharging any type of battery is that slow charging is better for it than fast charging. So . . . . if you don't really NEED it to be recharged quickly, then why would you not opt for the slowest charge which still meets your needs of use of the vehicle, just to be on the safe side??

90% of the time, we put the car in the garage for the night around 8 PM or so and we don't need it before roughly 8 AM the next morning (sometimes even later) so why plug it into Level 2? - It gains us nothing

Your knowledge, expertise and experience may be different - I suspect that long before the 8 year 100,000 mile battery warranty is used up, we'll be reading here about some who are having battery problems and even more interesting, what Mitsu will be willing to do about it, if anything. We don't put as many miles on ours as most of you do and we use Level 2 pretty sparingly, so I *hope* I'm not one of the first to have to deal with Mitsu about getting something fixed. Hopefully by the time I need it, Mitsu will already have made some decision about what they're willing to do for 4 or 5 year old cars which only have a range of 30 or 35 miles, if that comes to be the case

Don

I've calculated the Ah capacity from a different direction and agree with Don's 48.5 Ah figure. That's a strange rating, as the only SCiB cells I've seen photos of were rated 20 Ah, but possibly at the more common C20 rate. C1 is a more practical rate for our cars. Toshiba tests SCiB cells through full 3C discharge and 3C recharge to 6000 full discharge cycles and gets 85% remaining capacity. http://www.scib.jp/en/product/detail.htm That would be 372,000 miles on the odometer (our cars discharge at a max rate of 3.09C but only recharge at 0.24C on Level 2 (16 amps at 240V = 11.6 amps at 330V), and a laughable 0.06C on the stock Level 1 EVSE. That puts Level 2 recharge and regular driving waay down into the flat part of an extrapolated cycle life curve, if it doesn't fall off the cliff after 6000 cycles. EVen if we keep the pedal to the metal and only get half of the EPA rated range per charge, that would be 186,000 miles on the odometer with 85% battery capacity remaining. I think that Mitsu engineered this car with a lot of headroom on the battery warranty, and overheated packs are a far greater concern than any available charge or discharge rate. The Toshiba tests were carried out at 25 degrees celsius, or 77F. Data on the battery life at higher temps would be nice...

And oh yeah, 0.24C recharge is indeed better than 10%, but it's only 8% of the car's design discharge rate. You'll notice that Toshiba's cycle life testing used the same C rate for charge and discharge. Also of note in the Toshiba crush test video on that page is that the cell is labeled as being charged to 2.8V, but begins the test at 2.67V.
Jay

I sure hope you're right, Ray. As you mentioned earlier, there are already Leafs which are down to 85% of capacity after just one year . . . . hopefully they'll stay there and not lose much more over the next 4 or 5 years

I was really leary of Mitsu's battery warranty when I first read it and then when we went to buy the car, they had us sign all sorts of arbitration agreements while explaining that reductions in range were to be expected and were a normal part of aging, which really made me think the warranty was only good for a complete failure of some sort

I really do hope we can all drive our cars over 6,000 charge cycles and still have 85% of range remaining, but I'm still pretty sceptical. To get the most use from the car, we have both Level 1 (13 amp) and Level 2 charging available, but we use only the Level 1 for almost all charging . . . . just to be on the safe side. I still believe that slower is better, especially in the warm climate where we live. I also make it a regular practice to let the pack cool for a couple hours after the last use before I put it on the charger

Don

On this topic of 'stroking batteries in hot weather' the owners manual mentions that if the car is driven in temperatures over 104F/40C uphills or on highways the turtle light might go on, the regen will be reduced and several other things will take place to protect the traction battery. Has anyone ever experienced this?

I was talking to Tony Williams over on the My Nissan Leaf forum and he's said that his battery pack has been exposed to 130F temperatures and nothing has happened. The Nissan Leaf is supposed to go into turtle mode at 122F/50C. Definitely sounds like the Leafs batteries are not being protected from extreme temperatures.

Ok, so the Leaf battery issue has officially hit the fan with a class action.
http://insideevs.com/nissan-responds-to-class-action-suit-over-leaf-batteries/
Any chance Mitsubishi will respond by releasing more information about exactly how our batteries are being managed and what the best charging regimen is?

I think Nissan is trying to sidestep on this issue instead of fixing the problem. They do have an 80% 'battery saver' charge function in their cars, but we do not and nothing in the owners manual says not to charge to 100%. Nissan has also said the car should not be driven more than 7500 miles in a year! That is like 20 miles a day! Instead of admitting they made a poor choice in the Battery Thermal Management System (or lack there of), they are pushing the blame on the consumer. I had an exchange on a thread in the Leaf Forum this morning with Tony Williams who stated their owners manual says that the car will start shutting down at 50C where as ours says 40C. Tony also mentioned that his batteries have been exposed to 130F temps and nothing has happened. That is why I asked the question on this thread, to see if anyone here has driven their i MiEVs in temps over 104F/40C and what happened when they did? It would be an interesting comparison to see how well the technology in our EVs is compare to what is happening with the Leafs. Our instrumentations are very minimal and we have very little information about how our cars are doing compared to other EVs. We need to crack the OBDII port and make a LeafScan for our cars so we can get at that information as the Leaf owners have done. I've been looking at Lincomatics and Chris Howells LeafScan and thinking we could start there and make some modifications.

I'm using this thread as a placeholder for the following:

Before I lose track of these again, there are two recent studies/reports on Lithium-xx batteries and what factors extend their life. Slightly different takes between the two.

Presented at the 245th National Meeting of the American Chemical Society (same topic, three different writeups):

http://static.schneider-electric.us...e Charging/EV Customer Letter EV Cord Set.pdf

http://insideevs.com/scientists-con...nently-shorten-life-of-lithium-ion-batteries/

http://www.sciencedaily.com/release...encedaily+(ScienceDaily:+Latest+Science+News)

Summarizing,

Temperatures over 86degF (30degC) are not good for batteries (BUT, if I understand correctly, that depends on the individual battery chemistry formulation, discussed on EVDL). Especially important NOT to have the battery fully charged AND exposed to high temperature.

Now that summer is here, I always try to park the car in the shade and am happy I have a white car. Good news is that a battery life of 20 years is feasible if they're treated properly.

The other study is by a PhD candidate Jens Groot and referenced here (thank you John Annon):

http://evmc2.wordpress.com/2013/04/24/jens-groot-and-li-ion-battery-testing/

The report itself:

http://komar.bitcheese.net/files/JensGroot.pdf

and is also painfully addressed in the two-hour April 5 2013 episode of EVTV

http://www.youtube.com/watch?v=u6paZdk2JcA

(I don't suggest watching that unless you are really really interested in battery chemistry and can tolerate Jack's ramblings. Suggest jumping to close to the end of that episode for the summary).

Anyway, the conclusions are a bit different than the other one:

1. Temperatures up to 45degC (113degF) are readily tolerated
2. Repeated high currents (both driving and regenerating) are no problem
3. Batteries are most happy at a 50% SOC (State Of Charge)

For myself, I've revised both my operating and charging regimens to try to keep my iMiEV fuel gauge between 5 and 12 bars and only fully charge just before starting off on a longer trip and try to never go above about 14 bars on a hot day. I charge often to keep the pack within those limits, but always try to allow the pack to first cool down before charging.

You can read it here

http://blog.evtv.me/2013/04/2177/

There is also a link to the video on this site. I prefer the ".mov" version but my DSL-1000 takes 18 hours to download it.

Jack was made aware of his "bioblasts" and since that time did edit some of them out before publishing videos.

Jack and John Hardy did a lot of experiments with quick charging and normal charging. They do know what they are talking about.

Tomorrow I am looking forward to meet my first quick charger (CHAdeMO and SAE) and the man who invented it and builds them. His company has experience with CHAdeMO and i-MiEV. What they are saying sounds very much like Jack. I hope I will be wiser after that.

I did not charge for two days and I guess after meeting them my battery will be about 25%. Not a big deal and I have all my cables and adapters in the trunk but on the other hand I will take two girls on the ride, my wife and my boss (in parliament). So I will need the heater. Weather report says rain and about 10C or 50F.

Cheers
Peter and Karin

I think they do know what they're talking about, but a 2 hour video? I hope it's a lot more exciting than the first 10 minutes. (That's all I could sit through.)

No CHAdeMO but another unplanned bottom balancing :mrgreen:

We met the CHAdeMO people and parked side by side with a Nissan Leaf. Learned a lot. Watched the Leaf charging without noise from either the leaf or the Charger.

Moved some red tape. Hope we can feed the CHAdeMO charger so it will return and stay for good.

Time was pressed so we agreed to let them home. Three power sockets close by so really no need to keep them. Miscalculated the girls weight a bit and the final passage uphill took 4 bars. Returned home with the final bar and the turtle raising a warning finger. (no, the turtle did not really wake up.)

Cheers
Peter and Karin

I wonder which finger the turtle was raising... :mrgreen:

peterdambier said:

Miscalculated the girls weight a bit and the final passage uphill took 4 bars.

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That's one thing I like about Peter's posts. He never omits relevant data points, no matter the peril!