A123 20Ah O.K for winter use.

I was wondering now that the A123 20AH pouch cells are so "hot" and cheaply available, did anyone do a cold weather test on them, as in sticking a few cells in the freezer and run a few cycles through them just to see how they perform capacity, charge and- discharge wise.

There seems not so much info on the net or on this forum about how they hold up in colder climates, like 0 to -10 celcius ( or moderate wintertime ) it would be a real pity if everybody says "ooh and aah" about these cells "in summer" and buying them like madman, just to come to the conclusion that they are rubbish in winter and afterwards maybe even kaputt.

Does anyone has some real time experience in cold weather????

The A123 20AH spec sheet states:

Operating Temperature: -30c to 55C

That's a good indicator that it should work in colder temps. Of course, I haven't tried the freezer test!

The A123 spec sheet does not indicate charging temperature range.
From personal experience of using these cells (*) in my motorcycle project I found that charging these cells in low temperatures (between 0C and 10C) has a very bad impact on their internal resistance and capacity.
From (unfortunately) subsequently obtained generic information (obtained at Battery University site) on lithium cells, it is best not to charge this chemistry at temperatues below 10C.
Perhaps A123 requirements are even more stringent than that, but it ain't on their spec sheet.

(*) this was from 72 cells obtained via Cell Man a couple of years ago. Perhaps A123 have improved their secret sauce since then.

That shouldn't be a big issue for me. Just bring the pack inside to charge. If you know it's not good to do then it's simple to avoid.

I have read somewhere that they should not be charged under 0C.

ambroseliao said:

That shouldn't be a big issue for me. Just bring the pack inside to charge. If you know it's not good to do then it's simple to avoid.

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Yep, that's pretty much what I do these days. I just ride my motorcycle into the living room and consider it an ornament at that point. The pack also gets kept cool in summer by the house A/C then.
You definitely need to be able to trust your batteries, BMS and wiring skills to leave such a potential fire hazard indoors though.

totinen said:

I have read somewhere that they should not be charged under 0C.

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You will likely see reduced cycle life, reduced capacity and increased IR below 10C. I never charged as low as 0C, probably 3-4C and, if my A123's are representative, it's just not worth charging them in those conditions for the hit the cells take.

not A123 quality stuff.. just regular 2C ebk pack from the era..

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

[youtube]PzoyfFuwDKE[/youtube]

also see:

http://ypedal.com/Skidoo/Index.htm

Is it also ok to always store them at full charge?

Depends on how fussy you are. Personally, I don't get it how you can use an EV daily or more if you don't keep it charged and ready to ride.

I would say avoid putting a frozen battery on a charger. One way to avoid that is to charge it before it can cool off. It may warm itself slightly when discharging, enough to be above freezing anyway. If it's really that cold, you do want to insulate the battery box, and possibly even warm it gently when parked. A reptile cage heater pad would be perfect for plugging in a battery to a heat source. Very gentle heating.

a fully charged battery in room temp conditions, will deliver almost full capacity in the cold down to 0 celcius, however a cold battery will not fully charge from depletion in the cold using your standard charger, so should be taken back to room temps and stabalize prior to charging it.

I found that at -20 celcius the A123 cells could fail to start a cold 800cc 2 stroke snow mobile starter motor, ( 2P pack of 26650 cells.. ie : 4.6ah 12v ) .. at -10c it " works " but barely.. between -10 and 0c seemed fine ( this is Cold Cranking Amps, not capacity measure ) We tested the starter with a clamp on amp meter and show aprox 40 to 50 amps required to kick over that monster, so that's 10C discharge rate from A123 26650 cells at 2P

Bottom line, riding in cold weather below 0 celcius sucks.....

So I understand it's not good to charge under 10 celcius and increasingly worse towards freezing, but this is just the charging part and is maybe not telling the whole story, what about discharging or storage in cold weather, can I just let the packs sit on the bike when it's in my garage, it sometimes dips under 0 celcius in winter ( non insulation ) and it happened on some occasions that I had to heat the waterpipes to get water running again ( lucky never had a burst :? )

Do I need to make the packs detachable from the bike and take them inside to charge, store for longer periodes... etc etc, and then what about discharging, for instance, I put the packs on the bike, but get interupted for some hours before I can drive it, the packs will cool down towards 0 or less, but take it for a spin anyway, would this be harmfull too???

If so, I can not use A123 for about 3 to 4 months a year, if I want near maximum life out of them, I know that my current Thunderskies have huge voltage sag in wintertime like 10 volts under 2000 watt load in a 18s configuration ~58 volts no load, but stay good in capacity in summertime ( I think they still manage to get the rated 20 Ah, but never tried, I'll stop discharging @ 18 Ah ) this is after 2,5 year of use.....and I'm slowly looking for a replacement to have more output
I overcome the voltage sag to downtune the controller somewhat to about 1500 output, same top speed, but slower in acceleration, this is purely between my ears ( fear of damaging the cells ) but maybe not even necessary

I think it's weird that the company spec sheet suggests operating temps from -30 to 55 celcius, but one can not charge under 0 degree without ( permanent ) damage, is that why the modules from cars using these cells have watercooling but maybe also for preheating for cooler temps.

it's more about performance hit.. than damaging the cells.. imo..

To clarify what I was saying,,, If you can't bring the pack inside and warm it up, which would be ideal, then at least charge it when it's warmest, like immediately after your ride. Better than letting it cool off even more. If it's that bad, hopefully the discharge warms them in the insulated box enough to charge it.

Later on, when the battery is very cold it will suffer a capacity loss. So if possible keep a battery toasty with a gentle heater when you can plug one in, rather than let it freeze while you are at work or whatever.

The best I can do is, make the battery packs detachable from the bike and bring them in the living space to charge and storage just to be sure, only bring them out for a ride ( directly ), last winters were not that cold anyway, maybe only 2-3 weeks of real cold temperatures and the rest in the 0 to 10 degree area.