Arduino automated Li-Po warmer for Winter-conditions

[underdog]

Hello.

E-Biking in Norway during winter season can be a challenge with ebike batteries. On my bike I am not going to have a easily removable pack this winter. So I am considering to build a semi-automated system using a arduino mini into the pack enclosure.

Using a aluminum enclosure 146x222x55mm, I have figured that I can theoreticly fit 20pc 5000mAh 20C Turnigy cells, 10S2P for a 370Wh configuration. That leaves just enough space for heat insulation and electronics like BMS, Volt-display, connectors, main circuit braker, DC-DC converter, arduino and heater mat.

I am thinking of having a pre-drive heating function that takes the temp in the middle of the pack from a thermistor and warms it to desired temp automaticly when switched on, using a heat mat underneath the cells, cutting when desired temp is accomplished.

Mathematicly it seems for me to be worth while, even considdering the powerloss that heating will take from the pack....
Does anybody have any experience with this kind of a setup? Dangers, drawbacks, and so on?

 

[mistercrash]

I used an automotive battery warmer and an aquarium thermostat to rig up something to wrap my battery with to warm it during winters here in Canada. I bought the 80 watt warmer at an automotive store and the thermostat was found on ebay.
I placed the heat sensor on the outside of the cells instead of in the middle. The reason being that this warmer is powerful and I didn't want the outside cells to heat up to maybe 45 degrees before the temperature of the middle cells are warm enough to trigger the thermostat. I would rather have the thermostat clic on and off many times and let the outside cells transfer heat to the middle cells slowly and not get too warm doing it. Once the whole battery is at a constant 25 degrees, it should stay there with the help of the warmer and the heavy insulation I installed around the whole system.
I also found a cheap temperature gauge that I installed next to the thermostat and the sensor of that gauge is placed in the middle of the cells. This way I can at a glance monitor if there is a large difference between the temperature of the outside and the middle cells.

The battery warmer was $35, the thermostat was $20 and the temp gauge was less than $5.

 

[underdog]

Thank you mistercrash. The idea of using mulseveraltipel thermistors in different places is something I will look into.

Got the arduino mini R5, and realized it is TINY, and that it did not have a usb-port. damit. Also need some relays and stuff, so the project is still in pending.