LiFePO4 heating pad for cold temperatures

[Kristof]

The temp on those pads would worry me. That's really, really hot.

If you put this on a 1/4 inch Aluminum 2 inch strip it would heat the batteries really well I think. Putting the strips right on the cells would melt the plastic cover and probably create problems for the battery as well.

 

[HRTKD]

If you put this on a 1/4 inch Aluminum 2 inch strip it would heat the batteries really well I think. Putting the strips right on the cells would melt the plastic cover and probably create problems for the battery as well.

As well as aluminum conducts heat, I would test the snot out of that theory before I put in practice.

 

[Fpoet]

Am using these in my build:

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Buy GAOHOU Hive Electric Heater Plate Beehive,Silicone Heating Heater Mat/Pad,12V 12W Heating Baking Mats Save Honey Beekeeper Bee Keeping Equipment: Beekeeping Supplies - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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$10, 12 watts each, 100mmx120mm.

4 per side of these glued to an aluminum plate will just about perfectly fit my 4 x 280AH cells.

With combinations of parallel and serial connections, I will have the flexibility to drive 96 watts total in parallel, or signficantly less for a more gentle heat without the need for any additional electronics.

Plus I can change after building as needed by only swapping a few connectors,

I also purchased four of these, and received them yesterday. It will take a few weeks before I work on a proper insulated enclosure. Out of curiosity, I connected one directly to a commercial 12V LiFePo4 battery that I already had and measured 1,6 A with my Klein clamp meter. The pad itself did get warm relatively fast. I have different configurations in mind, so many tests to come.

 

[gecko]

The temp on those pads would worry me. That's really, really hot.

Yep, I looked at those a while back but took a pass. That's a pretty intense heat density.

 

[gecko]

Am using these in my build:

Amazon.com: GAOHOU Hive Electric Heater Plate Beehive,Silicone Heating Heater Mat/Pad,12V 12W Heating Baking Mats Save Honey Beekeeper Bee Keeping Equipment : Patio, Lawn & Garden

Buy GAOHOU Hive Electric Heater Plate Beehive,Silicone Heating Heater Mat/Pad,12V 12W Heating Baking Mats Save Honey Beekeeper Bee Keeping Equipment: Beekeeping Supplies - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

$10, 12 watts each, 100mmx120mm.

4 per side of these glued to an aluminum plate will just about perfectly fit my 4 x 280AH cells.

With combinations of parallel and serial connections, I will have the flexibility to drive 96 watts total in parallel, or signficantly less for a more gentle heat without the need for any additional electronics.

Plus I can change after building as needed by only swapping a few connectors,

If the flat size is right for your build dimensions it has a fairly low watt density which is good. I would be cautious about creating folds.

These pads are a totally useless gimmick for beekeeping. Any experienced beekeeper knows cold doesn't kill bees, moisture kills bees. An artificially warm hive causes the bees to blow through their available winter food stores and starve.

 

[Trabuco]

Yep, I looked at those a while back but took a pass. That's a pretty intense heat density.

Until they are wired in series...

4 of them fit the side of my battery 280AH bank just about perfectly.

I can run 4P, 2P2S, or 4S to change the power density.

And attached to a 40 pound heat sink I think the pad temp will be just fine in at least one of those configs.

 

[Trabuco]

If the flat size is right for your build dimensions it has a fairly low watt density which is good. I would be cautious about creating folds.

These pads are a totally useless gimmick for beekeeping. Any experienced beekeeper knows cold doesn't kill bees, moisture kills bees. An artificially warm hive causes the bees to blow through their available winter food stores and starve.

I was wondering about the beehive thing. Didn't seem right to me.

 

[Kristof]

Until they are wired in series...

4 of them fit the side of my battery 280AH bank just about perfectly.

I can run 4P, 2P2S, or 4S to change the power density.

And attached to a 40 pound heat sink I think the pad temp will be just fine in at least one of those configs.

Are you sticking them directly to the cells? Or the side of a box or something? Interested in comparing notes as I am going to be putting this into the battery box this week.

 

[Kristof]

Are you sticking them directly to the cells? Or the side of a box or something? Interested in comparing notes as I am going to be putting this into the battery box this week.

And a 40 lb heat sink is a lot of weight for the box!

 

[Trabuco]

Are you sticking them directly to the cells? Or the side of a box or something? Interested in comparing notes as I am going to be putting this into the battery box this week.

My current plan is to silicone them to an aluminum sheet and attach to each side of the pack inside the compression frame.

Still waiting on my cells from China!

 

[Trabuco]

And a 40 lb heat sink is a lot of weight for the box!

(the 40 pound heat sink would be the battery)

 

[Kristof]

(the 40 pound heat sink would be the battery)

Roger the battery! Here is a snap of my battery and the plan to run two pieces of aluminum strip down each side of the battery.

 

[DerpsyDoodler]

Roger the battery! Here is a snap of my battery and the plan to run two pieces of aluminum strip down each side of the battery.

I hope I am not speaking in err, but not sure running aluminum strip down the side of the battery is a good idea. Are those prismatic cells? Many brands are known to have a positive charge on the case. Contacting them with conductive metal is discouraged (in the event the thin layer of insulation on the outside of the case breaks or otherwise wears through).

 

[Kristof]

I hope I am not speaking in err, but not sure running aluminum strip down the side of the battery is a good idea. Are those prismatic cells? Many brands are known to have a positive charge on the case. Contacting them with conductive metal is discouraged (in the event the thin layer of insulation on the outside of the case breaks or otherwise wears through).

Hmmm.... Any Suggestions? Sticking these to the cells was also not a good idea in my mind.

 

[DerpsyDoodler]

Hmmm.... Any Suggestions? Sticking these to the cells was also not a good idea in my mind.

Only what I posted earlier. I haven’t done much research into this myself, yet. It’s kind of a back burner consideration right now. Perhaps a forum search for battery heating will turn up something.

 

[Matt-M]

Up here in New Hampshire, we haven't had the both sun out and temp above 32ºF at the same time for weeks. Thinking about possible heating solutions after reading this entire thread. Here is my plan...

For each battery pack (24V, 8 x 176Ah cells), place a sheet of 1/4" aluminum underneath. Under the aluminum, glue two of those Hive Heaters previously mentioned. They are 12V 1A each - wire in series so I can run directly from 24V. Have to some shims of aluminum on the underside as well so the heating pads don't get too crushed. Thinking about a layer of Kapton tape on the top surface of the aluminum as an additional electrical insulator. I don't think the aluminum cell bodies are electrically connected, but just to be sure. Repeat for each of the three parallel packs.

I am only interested in heating while charging - my BMS has separate charge and discharge cuts-off temps, and the discharge is much lower.

I also have a Simarine monitoring system and some of the shunts have programmable relays built in. So the plan is to have a high amperage relay control the heating pads' 24V supply. A 3PDT relay would allow putting one pack heater assembly on each contact for plenty of current margin, something like this. That relay would be triggered by two of the Simarine relays in series. The first programmed for temp under 35ºF and the second for solar charge controller amperage over about 1.5A. So the heaters would come on only when it is both cold enough, and I am getting enough current from solar to offset the heater loss and still have some left to do charging. Don't want the heaters running at night when there is no charging happening anyway.

Already ordered the heating pads and relay. Should have something testable in a week or so.

 

[DerpsyDoodler]

Funny thing. After responding to the post here yesterday, this thread popped up in front of my face.

Battery box heater with remote monitoring and control (wifi)

Inspired by some of the LiFePO4 battery warmer installs posted on here I thought I would do a version for my motorhome battery box. Purpose is to maintain a minimum temperature in the battery box to prevent triggering of the BMS low temperature cut off. Not heating the batteries themselves...

diysolarforum.com

Cheers!

 

[Horsefly]

For each battery pack (24V, 8 x 176Ah cells), place a sheet of 1/4" aluminum underneath. Under the aluminum, glue two of those Hive Heaters previously mentioned. They are 12V 1A each - wire in series so I can run directly from 24V. Have to some shims of aluminum on the underside as well so the heating pads don't get too crushed. Thinking about a layer of Kapton tape on the top surface of the aluminum as an additional electrical insulator. I don't think the aluminum cell bodies are electrically connected, but just to be sure. Repeat for each of the three parallel packs.

Yes @Matt-M I think you have the right approach. I am doing a 24V pack, but I bought one of the "hive heater" pads (misnomer name, apparently) and configured my bank as 2p4s instead of 8s. I put the heater pad under a sheet of sheet metal, with some silicone trivet pads under the heater pad. It was pretty cold in my garage, but above freezing. I hooked up the heating pad to the battery and checked the temperature over time. The desire should be that the pad heats, but heats slowly so as not to cook the cells. After a few hours (I can't remember how many) the cells were about 70°F at the base, and about 50°F on the top of the cells. The ambient temperature in the garage most of this time was probably close to 40°F. Remember this is with no insulated box around the cells.

Anyway, I became somewhat convinced that two of these hive heater pads would do pretty well with an 8s 24V pack. I was thinking of also putting some smaller pads on the sides as well, but will have to experiment some more.

 

[Matt-M]

Yes, a box to contain the heat likely helps. I didn’t do that because the pass-thru space in this RV is heated. Didn’t want to insulate from the heat. Of course the heater only runs when we are in it. Thus the heater pad option for when it is not occupied and the main RV heater is off.

waiting on parts...

 

[jwelter99]

Up here in New Hampshire, we haven't had the both sun out and temp above 32ºF at the same time for weeks. Thinking about possible heating solutions after reading this entire thread. Here is my plan...

For each battery pack (24V, 8 x 176Ah cells), place a sheet of 1/4" aluminum underneath. Under the aluminum, glue two of those Hive Heaters previously mentioned. They are 12V 1A each - wire in series so I can run directly from 24V. Have to some shims of aluminum on the underside as well so the heating pads don't get too crushed. Thinking about a layer of Kapton tape on the top surface of the aluminum as an additional electrical insulator. I don't think the aluminum cell bodies are electrically connected, but just to be sure. Repeat for each of the three parallel packs.

I am only interested in heating while charging - my BMS has separate charge and discharge cuts-off temps, and the discharge is much lower.

I also have a Simarine monitoring system and some of the shunts have programmable relays built in. So the plan is to have a high amperage relay control the heating pads' 24V supply. A 3PDT relay would allow putting one pack heater assembly on each contact for plenty of current margin, something like this. That relay would be triggered by two of the Simarine relays in series. The first programmed for temp under 35ºF and the second for solar charge controller amperage over about 1.5A. So the heaters would come on only when it is both cold enough, and I am getting enough current from solar to offset the heater loss and still have some left to do charging. Don't want the heaters running at night when there is no charging happening anyway.

Already ordered the heating pads and relay. Should have something testable in a week or so.

This is a good plan but the only downside is that you will need some mechanism to hold back the charging until the batteries get above 35F (or whatever you decide the safe to charge temp is). This is the tricky logic I'm trying to work out using a Cerbo GX (instead of the Simarine you are using)

I want heaters on when I am "ready to charge" (B2B putting out power, AC power supplied to MultiPlus, or Solar production) to get battery up to temp to then allow it to charge. I want that to happen quickly to not waste "charge time" if solar, B2B, etc.

So I may decide to just put the battery heater on a timer to come on a couple hours before daybreak when temp below 35F, or perhaps allow it to be powered continually when below 35F, depending on how quick it warms up the 80kg of batteries and how well the battery box maintains temp.

I plan to set the "discharge not allowed" signal once under the safe discharge temp to disable all loads as I presume any humans or pets in the RV are now frozen and do not need power.