In the previous post I did some testing of a battery heater system and the pads were able to melt XPS foam. I was concerned about this and wanted to do some testing with pads from Facon which are used in the RV world for tank heaters.

The Facon pads are desinged to be used at 12V and draw about 4-6 amps depending on your voltage. They have a built in hard-wired temperature sensor that turns the pad on when it is "near freezing". There is not a specific temperature mentioned.

I wanted to test these pads at different voltages to see how hot they get. I would not plant to use them with their own temperature sensor but rather with the DROK temperature controller I used in the previous test.

Modification

At first, I thought I had ordered pads without the thermostat they advertise because the it is just a pad with two wires coming out of it. I had assumed a thermostat would be am external device. I was wrong. The thermostat is built into the pads. It is inline with the positive wire, under the foam approximately 1 inch (2.5cm) from the heating wires. I believe as-is the heater would likely cycle on and off quite a bit as the thermostate is sensing the temperature of the pad and not the ambient air or the tank\battery it is heating.

To modify the pads, I pealed back the glue, and the black tape covering up the positive and negative wires. I then cut the positive wire, removed the thermostat and used a wago connector to rejoin the wires. In this configuration I used my benchtop power supply to test the pads at various voltages.

Test Results

Voltage	Amps	Temp (F) Range
25	8	Hot very quick
12	4.7	115-145 F
5	2	90-95F

At 5v, and in an enclosed space, I think these heater pads would be perfect for batteries. They are not going to melt anything and they will keep the batteries warm. You could argue they'd heat more slowly than at 12V but I think that is more of a benefit than a problem.