Good morning, I'm a new member. I see a few Threads about BMS boards without temp protection, and BMS boards "with temp protection" cut-off temperatures set too low. I have built the following system for my own RV (stored in a COLD garage through the Winter, and subject to cold AM temperatures in early Spring Camping.
Independent of any BMS built into an existing battery pack, I use a cheap 12v "fridge controller" (thermostat with temp display) programmed upside-down: Its low-power Relay contacts switch "ON" when the temp Sensor falls below 38 degrees Fahrenheit, and then turns back "OFF" when the temp Sensor reaches 50 degrees. But I don't have an actual heater connected to the Fridge temp Controller. Instead, I have only a low-current 12v circuit (from the battery) which will drive the coil of a big 5-pin automotive "Power Relay".
The "common" power leg (pin 30) on this Relay comes in from my charging Source (a Power Converter). In normal conditions, when the relay coil is unpowered, power goes directly to the +12 Volt Battery Power Distribution Bus, and the batteries can be charged. (I have 3 somewhat small LFP batteries in the RV.) But, in cold temperatures, the "Power" Leg is switched away from the batteries and instead goes through some relatively cheap heating pads, made for motorcycle seats, which slowly warm the battery cases. When the entire compartment has warmed to 50 degrees, the heater pads are turned off and charging begins. Diagram:
Independent of any BMS built into an existing battery pack, I use a cheap 12v "fridge controller" (thermostat with temp display) programmed upside-down: Its low-power Relay contacts switch "ON" when the temp Sensor falls below 38 degrees Fahrenheit, and then turns back "OFF" when the temp Sensor reaches 50 degrees. But I don't have an actual heater connected to the Fridge temp Controller. Instead, I have only a low-current 12v circuit (from the battery) which will drive the coil of a big 5-pin automotive "Power Relay".
The "common" power leg (pin 30) on this Relay comes in from my charging Source (a Power Converter). In normal conditions, when the relay coil is unpowered, power goes directly to the +12 Volt Battery Power Distribution Bus, and the batteries can be charged. (I have 3 somewhat small LFP batteries in the RV.) But, in cold temperatures, the "Power" Leg is switched away from the batteries and instead goes through some relatively cheap heating pads, made for motorcycle seats, which slowly warm the battery cases. When the entire compartment has warmed to 50 degrees, the heater pads are turned off and charging begins. Diagram:
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