LiFePO4 Battery Heater
Honey, It’s Cold Outside
You can buy a LiFePO4 Battery (commonly known as a Lithium battery) with a built in heater, or at least a Battery Management System (BMS) that has a low temperature cutoff. This is what I’d recommend you do.
If you insist on ignoring my advice, as I frequently do, this is how I went about building a non intrusive battery heater. Note that I am not an electrical engineer, a heating engineer, an electrician, or even considered competent in any skill required to do this job. You really should buy a ready made battery suitable for subzero conditions.
LiFePO4 cells will freeze in low temperatures and attempting to charge a frozen cell will damage it. My Poweroad battery gives a minimum charging temperature of 0c (minimum discharge is -20c). As far as I am aware, the BMS in this battery does not have a low temperature cutoff. When I bought the battery, I didn’t consider this to be an issue, since I was planning on heading south for the rest of my winters.
Due to a change in plan, I find myself looking out the window at a very snowy UK. The internal temperature of the van was -3.5c this morning. I have had to disable the various chargers to avoid damaging the Battery.
I have a three step plan to keeping the batteries above zero
- Battery Heater
- Insulation
- Diesel Heater Vent
Battery Heater Parts list
Battery Heater Instructions
Tape the heater pads to the battery case using aluminium tape.
Ideally they should sit underneath (heat rises), but as my batteries sit directly on the floor, I was concerned about damage to the heating elements, so I just put them one on each of the long sides of the battery.
The heaters come with a switch for low power, high power and off. I removed this switch, you only need the high power setting. Each heater draws around 0.75 amps when heating. Using the two pads, I measured a power usage of around 3 amp hours (approx 40 watt hours) over 24 hours in subzero temperatures.
Connect the heater pad positives to the K1 terminal on the W1209 module.
Connect a fused positive supply from the battery to the +12v terminal and bridge it to the K0 terminal. I used a 4 amp fuse for 2 heater pads.
Connect the heater pad negatives and the battery negative to the GND terminal.
Tape the thermocouple to the battery box with electrical tape. Secure all cables using electrical tape to give a tidy finish.
W1209 Settings
Press Set button. Use the + and – buttons to set a temperature you want to maintain. I used 2c. Wait a few seconds and let the display return to the current temperature.
Press and hold the Set button. P0 is displayed. Press Set and use + and – buttons to select H. Wait a few seconds and let the display return to the current temperature.
Press and hold the Set button. P0 is displayed. Press the + button so that P1 is displayed. Press Set. Use + and – buttons to set 0.5c. Wait a few seconds and let the display return to the current temperature.
All other settings can be left as default.
Using this configuration, when the temperature drops below 1.5c, the relay will close. A red LED will be displayed and the heaters will be powered. when the temperature rises above 2.5c the relay will open, the red LED will no longer be displayed and there will be no power to the heaters.
The heaters were able to maintain this temperature across 24 hours of just under 0c temperatures. What the temperature inside the battery case was is unknown.
Other Measures
A basic battery blanket made from Aluminium bubble wrap insulation.
We already have a 2kw diesel heater in the van, so an addition of a vent in the battery box will allow some heat into the battery box when the heater is running.
All these combined should give us a battery that never freezes. So far it’s been tested down to an internal temperature of the van of -5c.
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