Battery heater pad question.

Hello,
I purchased RV tank heater pads that will recommends but on the pads it speicfies NOT to attach to conductive materials and a lot of the insulating foam material I use has metal foil and the housing of the batteries are metal as well.
Will recommend attaching it to sheet metal.
Have any of you stuck it to metal objects that you have attached it to?
How did it work out for you guys?
Thanks.
I have a half dozen battery systems I have built for people I need to protect from freezing.

Bump...

I did a search for this exact question. I want to attached the Focon 12x18 heating pad to an aluminum heat spreader plate, cut to the size of the bottom of my battery box. Insulation underneath, heat radiating/conducting up through the thin aluminum sheet (~0.025") into the bottom of the battery cells. When I got the heaters, they say, "do not attach to metal surface." Will attaching it to a sheet of aluminum impact the controller operation? Is there a fire issue? I just don't get it. I know that most RV gray/black water tanks are polyethylene plastic. I hate it when reality stands in the way of a good plan.

@Will Prowse

Any suggestions?

I got a Mica plate (microwave repair) and attached the heater to the Mica. Mica is electrical insulation and heat transparent.

Thanks @Rocketman, this seems like a great solution. Did you understand why you did what you did? I may do the same but I just don't understand why a 12x18 piece of aluminum attached would change the performance of the temp controller so significantly. Hmmm...

Clearly this is not the intended use for this "tank heater." Does it cause the controller to cycle too frequently?

@Will Prowse
Have you found any issues with this pad?

My battery box - wood on the bottoms, then I have the Foncon heat pad - it’s glue is attached to the Mica. Then the Lishen 272ah cells sit on it. I have eight of them.

I have a Batrium bms - it can turn on a relay that I use to provide power to the heat pad - that way I can control when the pad uses the precious power. I didn’t like the default range of the Foncon heat pad.

My batteries in my MotorHome are basically outside. With the heater and a wood box around the battery and an insulated- I haven’t had any problems with cold. When it’s in the mid-20’s in the morning- the battery stays at 38 to 42 degrees. Any colder and my home has wheels…

Good Luck with your project

Thanks for your responses.

To be clear, I have not set up or tested anything here yet. I just re-watched Will's video. He uses a thin aluminum sheet to attach the heating pad to. The aluminum sheet I would use is a bit thicker. As I say above, about 0.025 [in] thick.

All this is about the explicit instructions on the heater pad, do not to stick the heating pad to a metal surface. I am trying to understand why they would state that?

I guess I will try the aluminum sheet first and see if that works. If it doesn't, I will try some Mica. Wish me luck.

I have one of these under my battery bank, and did as will shows in the video. Test your Facon heat pad before you install it, and do so in real or closely simulated conditions. I did not, and have them installed on my RV tanks, and one under my battery bank as described in Will's video. But they all seem faulty. When I turn them on, they all draw some amperage, but then they cut out (even with the temp well below 45 F. If you read the comments on Amazon for these tank heater pads, they seem to have reliability problems---either they do not work at all, or seem intermittent. Mine basically switch on and off, but never really heat anything. I do not recommend them. This fooled me, because when I wired them up, I turned on the switch, the switch illuminated (good), and my shunt reflected the increased amp draw. What I did not notice, was that after a minute or so, the amp draw goes to near zero (the switch remains illuminated). This was in 20 F conditions.

Facon does make a version WITHOUT the built-in thermostat. I have four of them now, and they all work. Description says they heat to 113 F. I have yet to place them in service on the RV, but so far in my workshop they all work and heat up nicely.

@constantspeed, this is great information thank you. I really don't want to build my batteries up on top of something that may or may not work.

You don’t need pads .. insulate your batterybox ( mine is 2 inches on 6 sides… ) .. I live in a cold mtn area… the heat from the batteries working at a reasonable load plus the inverter will keep it pretty warm in the enclosed area…
if things get really cold put a 50 watt light bulb and a small whisper fan circulating the heat and you will be fine ..Im in the second winter of doing this … works great…
everyone’s set up is different… all areas are different … everyone’s engineering skills are different You gotta self figure your need and answer…

i kept it in the 40s inside over a few days last year when it was -16 below F outside for two days…with a 50 watt bulb. Safe , easy ,it works….

insulation and keeping the battery’s working is the key….sry , no offense meant to pad sellers.
J.

The reason the heating pad says not to glue it to a metal surface is all it will take is a spot or two to wear through and the pad shorts out through the wear spots.

Not good…

Ah, makes sense. In the case where you have 8 280Ah cells sitting on top of the heating pad, bouncing down the road, I could see that as a problem. The light just came on. cheers.

Rocketman said:

The reason the heating pad says not to glue it to a metal surface is all it will take is a spot or two to wear through and the pad shorts out through the wear spots.

Not good…

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All true, but also depends on your build/scenario. The pad and sheet aluminum are pretty snug under my battery bank/box, and strapped down. More so, the batteries are in their own commercial cases (not DIY cells), and the pad is wired to the DC panel with a minimal fuse. So if it shorts to the sheet metal, the fuse will go quick, and the sheet metal is only in contact with Durarock and the plastic battery case material. But I would not do this under a bank of bare LiFePo4 cells with a DIY battery build. Agree that could be more sketchy.

Thanks guys, this is all helpful info. @constantspeed, can you define "bare LiFePo4 cells?" I have the EVE, blue prismatic cells, 280Ah. Is this what you mean? When you say commercial cases, I assume you mean something like a battleborn case?

I have my EVE cells in close fitting, furniture grade, really skookum plywood boxes. There will be very minimal cell movement, if any.

Sorry, I didn't quite get that before this discussion. I hear what you guys are saying, an abrasion short would be catastrophic without a limiting fuse to stop the energy flow to the heating pad. Thanks much for the feedback and discussion.

I am struggling to understand how Mica Sheets are thermally conductive? I understand their dielectric strength. I see them as a thermal break between the heating pad and the batteries. I get that they would be excellent in preventing a short.

kitebouyd said:

I have the EVE, blue prismatic cells, 280Ah. Is this what you mean? When you say commercial cases, I assume you mean something like a battleborn case?

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Yes, that is what I mean. I have Ampere Time and Li Time batteries---they are encased. I also have a build for my garage using those same Eve cells, and no, I would not place the heat pad and metal sheet in direct contact with them.

I would also suggest incorporating a version of what @JRH is saying, and build with the foam insulation panels you get from Home Depot. They come in 2' or 1" thick versions. Build this on all sides, and you have a good thermal box.

What kind of climate conditions are you trying design for, how cold?

What BMS are you using with your Eve cells, and how many cells? I have a JBD with a heat port.

kitebouyd said:

All this is about the explicit instructions on the heater pad, do not to stick the heating pad to a metal surface. I am trying to understand why they would state that?

Click to expand...

Have you tried turning it off and then back on?

In other words, have you tried the obvious but seems too simple: Have you yet contacted the manufacturer and asked them?

Maybe they’ll give you just a canned answer, but sometimes you get lucky and someone with actual knowledge answers.

6x 7.5W pads

installed recently. was suppose to be out camping this week in sub freezing temps, but couldnt go afterall. it all works as tested on the bench, looking forward to testing in actual conditions.

12vDC said:

6x 7.5W pads

installed recently. was suppose to be out camping this week in sub freezing temps, but couldnt go afterall. it all works as tested on the bench, looking forward to testing in actual conditions.

View attachment 178963

View attachment 178964

View attachment 178965

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Are those pads the cheap silicone ones like these? :

4PCS Silicone Heater Mat, Icstation Rubber Heating Mat 12V 25W Electric Blanket Flexible Mat Constant Temperature 80X100mm https://a.co/d/fFmIAAU

Tomthumb62 said:

Are those pads the cheap silicone ones like these? :

4PCS Silicone Heater Mat, Icstation Rubber Heating Mat 12V 25W Electric Blanket Flexible Mat Constant Temperature 80X100mm https://a.co/d/fFmIAAU

Click to expand...

correct. same but different.

in retrospect i probably should have used the polyimide type like this:
DONGKER 12V Polyimide Heating Film, 25W PI Polyimide Heater Plate 100mmx100mm Polyimide Flexible Adhesive Heater https://a.co/d/3b2V37d

you might be interested in this purpose made silicon for the DIY cell build:
SUNFUN