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Lifepo4 battery heater

Electry

New Member
Joined
Jan 29, 2022
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19
My plan is to buy 4x 10cm x 5cm 48V heater pads and use them under the alluminium sheet to heat the 24V battery bank during cold weather. Does my calculation make sense, and would the following wattage be enough to heat the batteries? I'm open to suggestions.

4x 48V heater pads would result in 10cm x 5cm = 50cm2 * 0.4 (heater pad specified W/cm2) = 20W per 48V pad. Connecting 24V battery to 48V pad would provide 1/4 watts (is that right?), so 5W per pad. 4 pads each 5W = 20W of total heat.

My main requirement is for heating pad to not exceed ~40C. Does anyone has experience with these pads and could tell me whether connecting 1/2 of specified voltage would drop the max temperature to ~40C, or it would be better to use something like 6x 24V heating pads (with 3 pairs in series, so 10W per pair, 30W total) Each pad would use maximum of 5W, so essentially it is 1/4 of the specified power.

Basically, connecting two 24V heater pads in series would result the same max power as connecting two 48V heater pads in parallel? Considering that it is connected to 24V battery.
 
Yes 1/4 power is correct when run at half voltage. I doubt anything close to 40C would be observed. Is there a thermostat involved?

20w is not a lot of heat in cold conditions. This is 8 cells right?
 
Yes 1/4 power is correct when run at half voltage. I doubt anything close to 40C would be observed. Is there a thermostat involved?

20w is not a lot of heat in cold conditions. This is 8 cells right?
I have recondisered the plan and bought 4x 40W heating pads, which should use total of 40W (10W each) when run at half voltage. It should be enough?

Yes, 8 cells. Heater pads would be controlled by external thermostat.
 
40w on 8 cells should serve you well. I have about 60w of silicone heat pads for 16 cells that has worked well down to about 15F in an unheated compartment. My heaters are stuck direct to the sides of the cells and the thermostat sensor taped to the top. Otherwise uninsulated. Heats slowly over about 20 minutes to rise 10F.
 
All depends on the amount of insulation. 20W + natural heat from the BMS is more than enough for my 16 LiFePO4's, with 2" of PIR around them, which are in regular use.
 
Some of the silicone heating pads can get quite hot. I'll be running four 12v pads in series to keep the temperature down. See my post linked below for the numbers:

 
I'm not sure if it's the pads or the thermostat but something is consuming a lot of power out of my LiFePO4 battery. I haven't put a meter on any of it. A week without a charge and the BMS shuts down. It's a small battery, so not a ton of capacity.
 

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