LiFePO4 heating pad for cold temperatures

[Kristof]

I have this aluminum hanging around. The LiFePO4 battery and box is already built. These strips will serve I am fairly sure - one on either side of the battery bank. But we shall see.

 

[Matt-M]

Got my prototype heating pad built today. The footprint of my battery packs is about 13.5" x 8.5", so that's the size of the heating assembly. Used those same 12V 1A "hive heaters" from Amazon, two per assembly. They have a bump where the wires attach:



Didn't want those bumps to get crushed too badly and maybe affect connectivity to the heating element, so I backed them with a silicone pad, and made cutouts for the bump and the wires:



Here's how they fit together - looking at the back (non-battery) side.



Used a piece of 3/16 aluminum for heat distribution and a thin piece of aluminum sheet for the bottom. In the "probably won't make any difference, but can't hurt" department, I painted the top aluminum plate black to absorb heat and polished the bottom aluminum sheet to reflect away from the floor:



Stacking it all together:





After it was all together I wrapped it in Kapton tape. Holds it together and maybe an extra "just in case" bit of electrical insulation facing the battery:



Gets installed with my third battery pack tomorrow or Wednesday. A bit more work to do the wiring, then will retrofit to the two existing packs.

 

[Matt-M]

Successful test last night. Wired the two pads in series and applied 24V from a bench supply. Current draw was 1A, as expected. Took over 10 minutes to notice any temp increase. After about 1 hour, top surface had reached 92°F. This was in open air - I don’t expect it to get that hot with the heat sink of the large battery in contact. Back surface only got to 73°F, so maybe the black paint and polished aluminum had some effect. The extra silicone pad also insulates the back side, so maybe not.

 

[Matt-M]

First heater installed,

 

[Kristof]

Hey so tests are ongoing and I have learned a lot so far.

First 4 X 7W heating pads on a 2 X 14 inch aluminum strip gets too hot, even on a heat sink. I also agree with most comments about a bigger piece of aluminum but I am using scraps and it seems to be working well.

I have also got the little heating controller working well - not after some miss wiring and a couple blown 3 amp fuses. The wiring diagram online here is off - download the actual manual from the website and use the wiring diagrams there. As you can see from my pictures it is now working and controlling the heating pads.

I am going with one pad and now am using three 2 inch bars with one pad each. I am testing the whole setup live on a battery with no insulation to check temps on the bars and time it takes to heat, current flow, etc. After 30 minutes or so the current draw was .21 amps at 12V (as expected) and it appears to be heating the battery at 1 deg F every 20 mins. This seems to be about right for my use and will keep an insulated battery from getting too cold. At least this is my opinion so far.

Another major point I have learned is that these little pads do not work well in series - but they do work as specified in parallel.

I will keep you posted on things as I get them installed in the actual battery banks.

 

[Kristof]

Today I installed the heating pads/bars in the LiFePO4 battery. I am now conducting an overnight test as it is supposed to drop below 0 cel. As you can see I set the temp control to start heating at 38 F and stop heating when the battery is 42 F. The little battery I have as a test 12V power supply has a charger on it that produces 1.1 amps - it should be able to handle the load if the temps drop far enough. going to leave this little rig for the next couple nights and see how it performs. This weekend the battery goes back into the trailer and wired into the current system as bank 1. Bank 2 is a lead carbon setup and the plan is to leave the power draw on bank 2 until we get to California maybe sometime next week with the LiFePO4 heaters on. That said we should not need the warmers when we are living in the trailer as the heat system will be on. This is really just for storage events to keep both banks above 5 cel.

 

[Kristof]

24 hr test complete. It did not get cold enough (close to freezing) in the garage last night so I upped the temp control to 50F late today. When I did that the temp of the battery was 48.4F. In an hour the battery was over 50F - so the pads and the bars worked very well. Happy with the test but will leave it for a few days and see what kind of AH the little battery draws to keep the battery at that temperature.

 

[Kristof]

Hey so good news.

I opened the garage early this morning and let the -1cel weather in. The battery heater system performed marvelously and did not use as much current to warm as I thought it did. I kept the battery at 50 Fah with no issues at all and the little battery it was on (12AH) had no issues.

Success.

Details of the system are as posted but here are the two main components:

https://www.amazon.com/gp/product/B076Y5BXD9/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B07P2RJDPL/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Pretty economical and with some patience works very well.

 

[Jean-Jacques]

Has anyone tried the new Volthium lithium batteries? They are made in Quebec Canada, and have low temp cut off, but also are self heating. Just wondering how well they are built.

Hello, I have not yet tried it, but interested as it is in my own province, if interested to watch a french youtube post even without listening to the french user he is showing the batterie's interior, I've submitted this same post to Will Prowse and only to him as he is always interested to compare different manufacturer quality, hoping this is not against Will's forum policy. link :

 

[technerd1988]

Why not just keep the batteries inside with you. we are uncomfortable at 32f so unless you like freezing, this will be fine. I have little 12v fans inside of each of my battery boxes in my RV and my batteries stay cool and between 40f to 75f which is whats comfy for me. I have a pretty large 12v system, just a tad over 1000ah. By the way when its cold the fans help the batteries bring in warmer air. What I did was use ducting to connect the intakes to another duct that goes up to the ceiling where the heat is(they are on the foor and mine is a heavy duty box truck with 4 inch thick pressure treated wood floors) I just wired a thermostat to the fans and they run when above 70f or below 40f. keeps my cells happy and is cheap to set up. I already had a weather station that reports both inside and outside temps and sends em to a web page for controlling my a/c

 

[TGPB]

I still like the zero voltage required controller for my battery heaters. The Honeywell T6031A1029 is very reliable , easy to install and uses no power to monitor or activate the heaters. Why add another energy eating control to you system when there is a battle proven control that has been used for generations. I found mine on Ebay for less than $40.

 

[technerd1988]

I still like the zero voltage required controller for my battery heaters. The Honeywell T6031A1029 is very reliable , easy to install and uses no power to monitor or activate the heaters. Why add another energy eating control to you system when there is a battle proven control that has been used for generations. I found mine on Ebay for less than $40.

Seriously why not just use fans like I did? Use the power your using already in your space to keep them at a comfortable temp 24/7? Unless your using them in a shed, which the battery heaters aren't such a bad idea..but then you'd have to worry about cooling too. Its so simple

 

[HRTKD]

I still like the zero voltage required controller for my battery heaters. The Honeywell T6031A1029 is very reliable , easy to install and uses no power to monitor or activate the heaters. Why add another energy eating control to you system when there is a battle proven control that has been used for generations. I found mine on Ebay for less than $40.

I spent half what you did on my two thermostats. I get individual control over the heat for the two batteries. The watts required for the thermostats is negligible.

Seriously why not just use fans like I did? Use the power your using already in your space to keep them at a comfortable temp 24/7? Unless your using them in a shed, which the battery heaters aren't such a bad idea..but then you'd have to worry about cooling too. Its so simple

When I'm actively using my trailer, the thermostats and battery warmers are turned off. It's when the trailer is in storage that I have the warmers active.

 

[technerd1988]

I spent half what you did on my two thermostats. I get individual control over the heat for the two batteries. The watts required for the thermostats is negligible.



When I'm actively using my trailer, the thermostats and battery warmers are turned off. It's when the trailer is in storage that I have the warmers active.

yeah but if you have them in storage and the heaters constantly run wouldn't this drain your batteries down? In that situation I'd just slap anderson connectors on each pack and bring them inside when not in use like I did until I went full time rv life. I even think the manufacturers who put heat pads into their batteries are dumb. You need to take care of these. All that does is make people think you can just set it and forget it which you cannot. Thats why they make bluetooth BMS now so you can see the stats in real time. Think about if you left the packs out at something like 0f and you werent there, those cells are not gonna be happy being drained all the way down and your not supposed to float charge these.

 

[HRTKD]

yeah but if you have them in storage and the heaters constantly run wouldn't this drain your batteries down? In that situation I'd just slap anderson connectors on each pack and bring them inside when not in use like I did until I went full time rv life. I even think the manufacturers who put heat pads into their batteries are dumb. You need to take care of these. All that does is make people think you can just set it and forget it which you cannot. Thats why they make bluetooth BMS now so you can see the stats in real time. Think about if you left the packs out at something like 0f and you werent there, those cells are not gonna be happy being drained all the way down and your not supposed to float charge these.

I have plenty of PV to keep the batteries charged. I'm down at the trailer throughout the winter to do maintenance. So I need the batteries there.

 

[Horsefly]

I still like the zero voltage required controller for my battery heaters. The Honeywell T6031A1029 is very reliable , easy to install and uses no power to monitor or activate the heaters. Why add another energy eating control to you system when there is a battle proven control that has been used for generations. I found mine on Ebay for less than $40.

I think you may be chasing a non-existent problem. My little digital thermostat only pulls about 80mA @ 24V when the heat isn't on. So a 280Ah pack could power the thing for 3500 hours, or about 146 days.

 

[HRTKD]

I think you may be chasing a non-existent problem. My little digital thermostat only pulls about 80mA @ 24V when the heat isn't on. So a 280Ah pack could power the thing for 3500 hours, or about 146 days.

Better add a couple more batteries! LOL!

 

[technerd1988]

Better add a couple more batteries! LOL!

you might as well just do the xiaoxang BMS like I did with the low temp cutoff as well as high temp cutoff. I have the 4s 12v version on each of my packs. I got two more coming with my CATL cells(8 of em 280ah). Im gonna have over 1000ah after I add them beasties.

 

[HRTKD]

you might as well just do the xiaoxang BMS like I did with the low temp cutoff as well as high temp cutoff. I have the 4s 12v version on each of my packs. I got two more coming with my CATL cells(8 of em 280ah). Im gonna have over 1000ah after I add them beasties.

I already have the Overkill Solar 4s BMS.

 

[exodus1]

If you are trying to use a lifepo4 battery in freezing cold temperatures, battle born just released a 12v heat pad for keeping the batteries warm without melting the case. This pad should work for any standard lifepo4 battery. Just slap it under your batteries and connect it to 12v and you are done.

I think it is over priced though. It can be found here: Click Here for battle born heater pad


If you cannot afford the battle born pad, you can use a septic tank heater pad. It works in the same way but may possibly melt your battery case if you are not careful. You can avoid this by adding some protection or a way to distribute the heat across your entire battery bank. I would personally put the batteries in a insulated container, then add a thin sheet of conductive material like sheet aluminum over the pad so that the heat it produces can warm up your entire battery bank.

Cheaper heater pad source: Click here for heater pad

I have a small 24 volt system with two 50 amp hour batteries. I built an insulated box with leftover 4" poly iso foil coated foam from a construction project with top lid. I use a Vivosun 6" x 8" reptile heat mat and digital thermostat combo from Amazon. It is an 8 watt 120 volt heater pad plugged into the inverter. I set it at 45 degrees and it works great even in the High Rockies at sub zero temps. Insulation is the key.