Something I found when when testing the heating function, but didn't get around to posting about it until now. I didn't find anything doing a quick search so I hope this isn't repetitive info.
When the low temperature threshold is met, the BMS will disable the charging MOSFETs and, instead, enable the heating port (connect the heating port to Negative side). Discharge MOSFETs will remain enabled, however.
So if you have a 10A heater connected to the port and to Positive, and apply a 20A charge, the BMS cuts off charging and you then see Amps flowing to the heaters. Once temperature release is met, heater port is switched off, and you begin to see 20A flowing into the battery.
All good there!
Problem begins when your charging current is LESS than the demand of your heaters. So lets say you now apply a 5A charge to your (cold) battery. The BMS cuts off charging again and enables heating. However, the heating pulls 10A of which only 5A are supplied by the charger, and the other 5A simply get pulled from the battery.
At that moment the BMS, effectively sees that the battery is no longer receiving a charge, so it disables the heaters and enables the charging MOSFETs. Charging resumes for about a second before thermal protection kicks in again, and this loop is created where the BMS alternates between charging and heating every second.
This would easily be noticed early mornings when solar output is very low, for example.
The way I overcame this was to use a timer relay module where the current for the heaters will flow through a dedicated relay instead of the BMS. The BMS heating port would simply trigger the module, which in turn will keep keep the heaters on for 5 minutes before disconnecting. At that point If the temps are still below the cold protection threshold, the BMS heater port will trigger the module for another cycle and repeat until the battery is warmed up.
Hope this helps
When the low temperature threshold is met, the BMS will disable the charging MOSFETs and, instead, enable the heating port (connect the heating port to Negative side). Discharge MOSFETs will remain enabled, however.
So if you have a 10A heater connected to the port and to Positive, and apply a 20A charge, the BMS cuts off charging and you then see Amps flowing to the heaters. Once temperature release is met, heater port is switched off, and you begin to see 20A flowing into the battery.
All good there!
Problem begins when your charging current is LESS than the demand of your heaters. So lets say you now apply a 5A charge to your (cold) battery. The BMS cuts off charging again and enables heating. However, the heating pulls 10A of which only 5A are supplied by the charger, and the other 5A simply get pulled from the battery.
At that moment the BMS, effectively sees that the battery is no longer receiving a charge, so it disables the heaters and enables the charging MOSFETs. Charging resumes for about a second before thermal protection kicks in again, and this loop is created where the BMS alternates between charging and heating every second.
This would easily be noticed early mornings when solar output is very low, for example.
The way I overcame this was to use a timer relay module where the current for the heaters will flow through a dedicated relay instead of the BMS. The BMS heating port would simply trigger the module, which in turn will keep keep the heaters on for 5 minutes before disconnecting. At that point If the temps are still below the cold protection threshold, the BMS heater port will trigger the module for another cycle and repeat until the battery is warmed up.
Hope this helps
