Lipo Cold Temperature Issues

[betarambo]

Time to tap the ES brain trust again...

In testing my 26" Oset this weekend I had a lot of issues and realized too late that it was because it was so darn cold. I left the batteries in the bike, outside overnight. Ambient temperature was around 28 F most of the day and probably a lot colder than that overnight. I was running 8 Zippy 6 cell batteries at 8 ah with 2 in series and 4 in paralell for a total setup of 12s4p 50V 32 ah.

My bike is originally a 20" Oset so it is designed for and used to pull under 100 amps. With the 26" wheel and not lowering the gearing to compensate I routinely see around 160 amps. In this cold weather I got as high as 225 amps and pulled voltage down to 40v on a charged pack.

Obviously this is not a good thing and it eventually let the smoke out of my motor.

So, without sidetracking too much into the smoked motor, I would like to ask what clever things you guys do when running in sub-freezing temperatures. I am thinking:

1. Keep the batteries in the house or camper until it is time to ride.
2. Use some chemical heaters somewhere in the battery pack to keep some heat, maybe wrap them in towels or something to keep from getting too much heat in one spot.
3. Maybe buy some of those lipo preheater bags.
4. Probably buy some sort of cheap temperature probe so I can see what is happening at the pack and adjust my strategies accordingly.

Any advice, recomendation, equipment suggestions or experience as to when to worry about heating them up and when to not hassle it is appreciated. I am wondering if I have been missing the boat on a lot of performance even on marginally cold days. Might it be worth it to heat up the batteries even when it is like 50 degrees? What would be the optimal temp for most power? How hot is too hot for them?

Thanks!

 

[Wheazel]

What I usually do:

Keep the battery at room temperature or a few degrees under depending on where I store them.
Have an insulated compartment for the batteries so the slight heatgeneration from them keeps them at a good temp.

Naturally, amount of isolation depends on alot of factors. But with some trail and error its not hard to get something that works well in a big tempspan.
My experience is that regardless of if a battery is claimed to work well to low temps, it performs much worse, at best.

 

[Ykick]

Room temperature before/after and some form of insulation during use is what works for me down to around 15F. Much below that and internal heating from use doesn't seem to keep up after 15-20 minutes, in my situation/experience.

I performed some non-scientific "kitchen tests" in my freezer couple years ago which seemed to indicate significant Voltage sag at low temperature didn't appear to be as detrimental on RC Lipo as similar Voltage sag at room temperature.

In other words, I tend to readjust LVC (low voltage cutoff) to allow for slightly more sag during use in cold weather.

Definitely need to be careful charging at very low (or high) cell temps though.

 

[dogman dan]

It's brrrr lately. For southern NM. But we do get a snow day from time to time, and that's when I generally have the worst problems with cold batteries.

Definitely start with room temp batteries if at all possible, but in fact I find that my lico performs a lot better if above 80F. Mostly, that's all you really need. Try to start with a battery at 60F or more.

Having them warm nicely by the end of the ride helps you little, if they are getting hot because the resistance climbs at the end. You need to start out as warm as conveniently possible. You don't want to have the batts finally perk up only on the last half of the ride. Snake heaters are a great way to keep a box at 80F without roasting your batteries too warm, if you have AC power. You could go so far as to put one in your battery box. Or install one in an ice chest. It won't melt the plastic. After leaving the house, the ice chest will stay warm quite a while. But starting out at room temp, it will be hard for the batts to chill off a lot before discharge starts warming them back up. So mostly, just don't let em sit out overnight in the cold. Store em cold is fine when you won't use them, but not the day you will use them.

Ykick says different. I think the smaller your pack is in relation to the load, the more it does make a big difference. I see little effect from cold when I'm pulling 1500w from 30 ah of lico. But if I pull 3000w from 10 ah of ice cold lico, it sags like mad. This was 30c stuff btw.

When it snows and I go for a truly cold ride to romp in the weird white stuff, I find the metal battery box just helps chill the batteries even more. So the way I built my box, I can have the batts get very cold in 15 min. So I need to get out the duct tape, and wrap a scrap of something that insulates around the box as best as I can. Normally, it's just the opposite, I wanted that thick aluminum to be heat sinking my lico all summer. So for me, it can be really bad when it's cold and wet if I don't cover my heatsinking battery box. Now that I can't make body heat anymore, I do little riding in less than 45F. But the other day when it snowed, my new fiberglass box seemed to help. No noticeable sag at the low watts I ride at now. Inside that box, the packs are now in a somewhat insulating coroplast box. I only pull about 1000w now riding dirt, and don't need to heatsink my battery even in summer.

 

[efMX Trials Electric Freeride]

hey betarambo,

great to hear some news on the 26" Oset build..

there is a canadian ev company that has battery cells for cold weather performance:
http://www.impulsegroup.ca/
http://www.rosspar.com/Batteries_Expert.php
rated to work down to -60degress C..
seem reputable as well..
here are some threads:

Made in Canada, eh? : http://endless-sphere.com/forums/viewtopic.php?f=6&t=43705
E-S Stealth Electric Bike Owners : http://endless-sphere.com/forums/viewtopic.php?f=6&t=23996&p=715997&hilit=ImpulseGroup#p715997
Rosspar : http://endless-sphere.com/forums/viewtopic.php?f=31&t=55766&p=831279

btw,
your killing us waiting on the oset big boy build..
please post up some pics & vids of the bike in action! :wink: 8)

In testing my 26" Oset this weekend I had a lot of issues and realized too late that it was because it was so darn cold. I left the batteries in the bike, outside overnight. Ambient temperature was around 28 F most of the day and probably a lot colder than that overnight. I was running 8 Zippy 6 cell batteries at 8 ah with 2 in series and 4 in paralell for a total setup of 12s4p 50V 32 ah.

My bike is originally a 20" Oset so it is designed for and used to pull under 100 amps. With the 26" wheel and not lowering the gearing to compensate I routinely see around 160 amps. In this cold weather I got as high as 225 amps and pulled voltage down to 40v on a charged pack.

Obviously this is not a good thing and it eventually let the smoke out of my motor.

So, without sidetracking too much into the smoked motor, I would like to ask what clever things you guys do when running in sub-freezing temperatures. I am thinking:

1. Keep the batteries in the house or camper until it is time to ride.
2. Use some chemical heaters somewhere in the battery pack to keep some heat, maybe wrap them in towels or something to keep from getting too much heat in one spot.
3. Maybe buy some of those lipo preheater bags.
4. Probably buy some sort of cheap temperature probe so I can see what is happening at the pack and adjust my strategies accordingly.

Any advice, recommendation, equipment suggestions or experience as to when to worry about heating them up and when to not hassle it is appreciated. I am wondering if I have been missing the boat on a lot of performance even on marginally cold days. Might it be worth it to heat up the batteries even when it is like 50 degrees? What would be the optimal temp for most power? How hot is too hot for them?

Thanks!

 

[bee]

Hey betarambo apologies for sidetracking your thread, I sent you a PM but it seems like you haven't noticed it.

I'm looking for the disc brake to go kart sprocket adapter that is used on oset bikes, gwhy mentions it here: http://endless-sphere.com/forums/viewtopic.php?f=28&t=48113#p750404

Would you be able to source these for us?

Thanks

 

[betarambo]

Thanks for all the tips! I went out yesterday and keeping the batteries in the house made a nice difference. Running 14S instead of 12S helped to as did the new 11.1:1 gear ratio (9T front 105T rear).

Yes, I can source the sprocket adapters. I have one on my bike now and it worked fine yesterday. In fact, with the new gearing I had a serious loop out, landed on my back on a rock and shattered my beautiful new rear fender. I'll go check my PMs now.

Here is a pic for now until I do the real write up. It is 100 lbs with 14S4P of 30c 8 Ah zippys or 90 lbs. with 14S2P. 26" bicycle wheels, boxer forks, lengthened swingarm 3", lengthened frame 6.5", direct mount bars, stock Oset controller and motor.