Best batteries for cold (below freezing) weather

[coolchinateacher]

It's starting to get cold. Most of the next thee or so months my commute will be below freezing. In fact the high temp for most days will be below freezing and the bike will sit out in it while I'm teaching. I know the SLA's the bike came with are not going to hold-up but deciding what to upgrade to is, well, wow. I've been reading and reading and reading about batteries here and still haven't made a decision. I had tentatively decided on a 16s 12ah pack of Headways as the price here is pretty good. Then I started reading about how the cold affects lipo and lifepo4.

Today I found a good source for a 20ah pack of 2c lifepo4 for a better price than the 12ah Headways. They have higher resistance and lower c-rate than the Headways but 40a constant should be plenty (30a controller) and maybe in the cold the higher resistance could be a bit of a blessing as it will heat the cells up more as they discharge right?

Am I on the right track or is there a better, but still cost effective, battery choice for extreme weather? (it gets very hot here in the summer)

 

[oldpiper]

There is a thread just a few down from this one nominally about SLA's in cold weather, but it talks about other batteries, too. Don't know how long your commute is, but if it's not too long, the most cost efficient solution might be to fashion a well-insulated wrap or box for the batteries while riding, then take them off the bike when you get to your school and bring them inside to an out-of-the-way corner of the room to keep them warm as possible. Otherwise, others here can tell you about alternatives better than I.

Cameron

 

[liveforphysics]

They have higher resistance and lower c-rate than the Headways but 40a constant should be plenty (30a controller) and maybe in the cold the higher resistance could be a bit of a blessing as it will heat the cells up more as they discharge right?

In these types of situations, the cells on the outside tend to stay cooler than the cells deep inside the pack. This results in the interior cells having greater capacity and lower internal resistance, which can easily lead to an out-of-balance problem if the pack is used in deep cycles. For shallow cycles though, and with a good BMS, it should be OK.

Also, if possible, remember to try to have the battery as warm as possible when you charge it. Charging a cold battery is always the hardest on them.

 

[ZapPat]

There is a thread just a few down from this one nominally about SLA's in cold weather, but it talks about other batteries, too. Don't know how long your commute is, but if it's not too long, the most cost efficient solution might be to fashion a well-insulated wrap or box for the batteries while riding, then take them off the bike when you get to your school and bring them inside to an out-of-the-way corner of the room to keep them warm as possible. Otherwise, others here can tell you about alternatives better than I.

Cameron

The removable battery box suggestion is to be considered, and it would simplify battery choice.

As far as temperature goes, avoid getting 2C rated cells as they will drop to 1/2C or worse as they get cold. Self-heating will help them keep warm, but you could only rely on this if you keep the batteries warm (bring them inside). Or else you will destroy them while the're still cold.

Also remember that Lithium batteries *hate* being charged while very cold, and the colder they are, the slower you've got to charge them.

As for formulations to choose from, I've heard that nano-tech type cells hold up to the cold better than other regular lithiums. Supposedly because the ions transfering the charge between electrodes are more mobile to start off with, so they can bear better being slowed down more by the cold. So maybe A123 cells would be good (but expensive), and I might be curious to try the new hobbyking nanotech battery packs myself this winter. Cold weather is also a problem for me, and it's getting here fast!

BTW I have used good lipos (25C rating from HK) in the cold with no problems, but do note that I store them inside in the warmth to be ready for use, plus I add some insulation to the pack too. Draining them while at -10oC or so can be OK if you limit your discharge rate a bit, but never charge them at these temperatures.

Hope this might help!
Pat

 

[coolchinateacher]

I've been in contact with the suppier. The 2c rate of the pack is what they set the BMS to by default. The cells are new A123 18650's... so, 30c cells. I'm thinking 15-20ah of these should hold up well at 2c.

 

[lifepo4ever]

They have higher resistance and lower c-rate than the Headways but 40a constant should be plenty (30a controller) and maybe in the cold the higher resistance could be a bit of a blessing as it will heat the cells up more as they discharge right?

In these types of situations, the cells on the outside tend to stay cooler than the cells deep inside the pack. This results in the interior cells having greater capacity and lower internal resistance, which can easily lead to an out-of-balance problem if the pack is used in deep cycles. For shallow cycles though, and with a good BMS, it should be OK.

Also, if possible, remember to try to have the battery as warm as possible when you charge it. Charging a cold battery is always the hardest on them.

when you say cold battery is always the hardest on them , can I do damage on lipo? because here in winter time i use my ebike and when i go out to see a friend i recharge the lipo at -10-15 below zero