Heating Battery with Hot Hands in Cold Weather

[gmihestean]

I read that temperatures under 60 degrees Fahrenheit can decrease your batteries range. If i was to use my 48v 22ah lifepo4 battery at temperatures ranging from 20-35 degrees Fahrenheit, could i throw in a hot hands pack in the same bag, say wrapped in a towel to diffuse the heat evenly? That way the battery would not lose any range. What kind of range can i expect at those temperatures without any heat source, and with a heat source such as hot hands?

 

[nutnspecial]

Yes it would help.

I'm seeing huge lipo sag if batteries are allowed to reach even close to freezing, so I'm guessing amount of reduced capacity will depend on how much people are drawing from their batteries. Low C draw would be minimal loss while approaching freezing.
Below freezing is likely another story but I don't know how bad it would get.

 

[spinningmagnets]

12V heating film comes in many shapes, due to car starting batteries in extreme cold weather. You could plug these into a 12V power supply (120 VAC input) on a timer, so that it warms the battery pack 30 minutes before you ride. Here's a quick google result:

http://www.amazon.com/Polyimide-Flexible-Thermo-Heater-Heating/dp/B00XBFYA0W

You could also warm the ebike battery using voltage from itself. Here's a golf cart DC/DC converter for accessories (lights/radio) 12-60V input, 1-30V out, 90W

http://www.amazon.com/dp/B00C9S5QNC...&sr=1&keywords=adjustable+step+down+converter

 

[dogman dan]

I got pretty used to as much as 25% less range when really cold, below freezing. But that was with a completely un insulated, metal box to carry the pack. Just insulating it would get back closer to losing only 10% or so.

Insulation, then the hot hands under it could work well. But not so great if the pack ever really reaches frozen state. It's just a lot of mass to thaw by then. So try to concentrate on insulation mostly, so the pack never really gets that cold in the first place.

If you need that hot pack every day to make it home, the answer is even simpler. You just need a larger battery in winter.

Using the battery voltage to heat up the battery is not ever going to make you have range. That's what a cold battery does anyway. It has high resistance when cold, and uses those lost watt hours warming itself up to a temp where resistance is lower.

But if you can park where you can plug in an AC powered battery warmer, that would be ideal. Or, just bring the battery in, so a warm battery in an insulated box or bag is all you need to have decent performance in cold weather.

 

[gmihestean]

12V heating film comes in many shapes, due to car starting batteries in extreme cold weather. You could plug these into a 12V power supply (120 VAC input) on a timer, so that it warms the battery pack 30 minutes before you ride. Here's a quick google result:

http://www.amazon.com/Polyimide-Flexible-Thermo-Heater-Heating/dp/B00XBFYA0W

You could also warm the ebike battery using voltage from itself. Here's a golf cart DC/DC converter for accessories (lights/radio) 12-60V input, 1-30V out, 90W

http://www.amazon.com/dp/B00C9S5QNC...&sr=1&keywords=adjustable+step+down+converter

That's a cool idea! I plan to ride 13 miles, fish for a few hours, then ride another 13 miles back home. While i am fishing there is no way for me to keep the batteries warm. It would be nice if i can just have the batteries warm themselves before i start my ride back home! Are there any cons to warming a battery from one extreme temp 25 deg F to another extreme temp 100 deg, then the battery will slowly cool down to 25deg F as i ride home by the wind, and then back up to 70 deg F once i put my battery inside my house. Do you think constant fluctuations in temperature would shorten the amount of cycles i would get from my battery in the long run?

 

[gmihestean]

I got pretty used to as much as 25% less range when really cold, below freezing. But that was with a completely un insulated, metal box to carry the pack. Just insulating it would get back closer to losing only 10% or so.

Insulation, then the hot hands under it could work well. But not so great if the pack ever really reaches frozen state. It's just a lot of mass to thaw by then. So try to concentrate on insulation mostly, so the pack never really gets that cold in the first place.

If you need that hot pack every day to make it home, the answer is even simpler. You just need a larger battery in winter.

Using the battery voltage to heat up the battery is not ever going to make you have range. That's what a cold battery does anyway. It has high resistance when cold, and uses those lost watt hours warming itself up to a temp where resistance is lower.

But if you can park where you can plug in an AC powered battery warmer, that would be ideal. Or, just bring the battery in, so a warm battery in an insulated box or bag is all you need to have decent performance in cold weather.

Wow that's a huge difference, great tip! I am not sure insulation will help in my case because i wan't to fish for a few hours and surely my battery would reach the outside temperature in that time. Insulation would help on my way home though, if i throw in some hot hands in my battery bag, the insulation should help my bag not lose as much heat from the wind. I think 30 minutes before my trip home i will throw in two hot hands in my battery bag which i will insulate some how. That will allow the batteries to slowly increase in temperature and retain that heat for my way home. I am not worried about the cost because i won't be making fishing trips more then once a week. I am worried whether or not heating the battery with hot hands will shorten the amount of recharge cycles i can get out of it though.

I am getting a 22ah lifepo4, so going bigger is not an option. I am hoping it will last for 26 mile round trips in below freezing temperatures.

 

[parabellum]

Wow that's a huge difference, great tip! I am not sure insulation will help in my case because i wan't to fish for a few hours and surely my battery would reach the outside temperature in that time.

Then you are doing something wrong, good insulation will resist temperature equalization for days, not just hours.

 

[gmihestean]

Wow that's a huge difference, great tip! I am not sure insulation will help in my case because i wan't to fish for a few hours and surely my battery would reach the outside temperature in that time.

Then you are doing something wrong, good insulation will resist temperature equalization for days, not just hours.

DAYS??? So you are saying i can ride for 13 miles in 25 Degrees Fahrenheit with 15 mph winds, fish outside for 3 hours, then ride back another 13 miles and my battery can still be close to 70 degrees Fahrenheit when i get home by using good insulation? How and why type of insulation are you speaking of? Are there some premade battery bags that offer this?

 

[spinningmagnets]

Are there any cons to warming a battery from one extreme temp 25 deg F to another extreme temp 100 deg

Yeah, I also think a well-designed insulation blanket will keep it from getting very cold over a several hours of fishing, no sweat, bro...I understand how counter-productive it seems to take energy from the ebike battery to warm the ebike battery, but...I just think that its nice to have that as an option. I'm not saying use it every day for every situation.

 

[dogman dan]

Yes you can insulate it enough.

It won't be what worked for me in a warmer climate, just a few scraps of foam. But a warm battery is 10 or 15 pounds of nice thermal mass. It won't cool all that fast if you start out with it at 70f or so, and then it warms itself some on the way. Something along the lines of a soft cooler, then some more insulation inside it should do the trick. All you need is to have the thing above 50f, for the trip home. It will warm itself some more again from there as you ride.

But,,,, as I said right from the start. If you are cutting it fine in summer, you will be screwed in the winter. You might need to add some capacity, like an emergency spare in the form of a small Lipo pack or something.

 

[Ykick]

Battery packs never, ever increase capacity overt time/use. Always a loss and cold merely exasperates any loss of capacity.

That bubble insulation used for shipping frozen Ham’s a pretty good, thin insulator. Probably better than nothing but I wouldn’t waste electrical energy warming a battery - best thing to do there is to use a larger battery in the 1st place.

 

[parabellum]

You could build a pack to fit in 1 of those cooler containers. It will serve as protection as well and can bring it home to warm charge and store if you use quick release.
http://www.rubbermaid.com/CategoryDisplay?storeId=30051&urlLangId=&beginIndex=0&urlRequestType=Base&categoryId=16042&top_category=&langId=-1&catalogId=30051

 

[dogman dan]

That's pretty large for carrying on a typical bike. But I was thinking more like modifying a soft insulated lunch box, or cooler, to make a jacket to wrap around a smaller battery box or bag.

No doubt, if you live where it's cold enough, maybe a trailer with an ice chest on it could be the way to go.

How about, order some mail order steaks, and use the shipping box. Usually they are very thick foam containers.

 

[parabellum]

That's pretty large for carrying on a typical bike. But I was thinking more like modifying a soft insulated lunch box, or cooler, to make a jacket to wrap around a smaller battery box or bag.

No doubt, if you live where it's cold enough, maybe a trailer with an ice chest on it could be the way to go.

How about, order some mail order steaks, and use the shipping box. Usually they are very thick foam containers.

We have very wide size variety here, from one just enough to put 2 Coca cola cans to one I can hide in myself. For OP this 1" layer of insulation, 2 additional PE protection layers and caring box in one package can not be considered lost space. I was modifying a motorcycle frame to fit cooler box where the tank was to optionally droop in box with extend range battery or a box with few cooled beer bottles. Then realized, I cant find any documentation to this frame. :lol:

 

[dogman dan]

Great if there is one the right size. I've just found the selection in stores in my area was either too short for a typical bike battery, or the ones long enough were 2-4 times too tall. It just depends on the actual size of the pack. Some smaller six pack coolers would be ideal for a 700 watt hour lipo pack. Fit six beers, fits 6 6s lipos good too.

But continuing to assume he's smart enough to have the pack in something protective, then he could wrap the outside of the tool box, ammo box, or whatever it is with a cut down soft cooler.

FWIW, one of the better insulated containers I've seen is the EM3ev triangle battery bag. Additional protection inside the bag still definitely recommended.