I live in Canada and the truck will sit for weeks at a time in the winter not being used so heating the battery constantly doesn't make sense. As such there is a lot more power required to recover than would normally be required to simply maintain because the battery will have to be pulled up from well below freezing when I want to use the truck and it would be nice it it could happen in half a day.
I dont know how much I need to explain so Im just going to stick my cartoon below and please feel free to pick it apart and ask questions. Any criticisms are greatly appreciated.
Major points that may not be obvious are:
I dont know how much I need to explain so Im just going to stick my cartoon below and please feel free to pick it apart and ask questions. Any criticisms are greatly appreciated.
Major points that may not be obvious are:
- Shore power is the default when plugged in
- Battery and alternator power via the DC-DC is the second option when not plugged in
- When it is below 5degC the BMS turns everything off so a manual switch allows power from the chassis system but only when engine running (Relay with coil power from fuel pump)
- The thermostat on the right controls the primary heat source. It controls two 120W heating pads in series for 60 watts total. Its thermocouple is on the top of the battery and the thermostat will be set to around 10degC.
- If Im in a hurry and/or have a long way to heat them up I can press the momentary switch coming off the output of the first thermostat which will energize the second thermostat. This controls a 120 watt heating pad and if I close the switch, it will also control a second 120watt heating pad. This thermostats thermocouple is in the 1" airspace between the aluminum heat transfer plate and the bottom of the battery. This thermostat will be set somewhere around 30deg
- When the first thermostat ( The one set to 10 degrees) reaches set point and opens the circuit, the relay controlling the second thermostat opens and deactivates the two 120 watt heating pads and does not reset. Heating from that point is done only by the 60 watt pads unless the momentary switch is pressed again.
- The battery is 16 cells and there is airspace between each cell so heat to the top of the battery is not by conduction through the battery alone. There will be a convection current moving heat as well.