A project log for Green BMS

Open source Bluetooth Smart Battery Management System

Sergio GhirardelliSergio Ghirardelli 09/30/2021 at 17:180 Comments

The BMS Battery Management System Limiter activates or deactivates the charging, according to Control Unit command.

When BMS balances just one cell of the pack, Control Unit commands the limiter relay, that forces the charging current to 1A, in order to stop charging the cells that have reached the balancing voltage (and are balancing) while continuing to charge the others.

Current limiter circuits includes a Mosfet IRFZ44N, a NPN transistor BD139 and a 0,68 ohm power resistors that can reach high temperature, for this reason you must choose a metal limiter case in order to dissipate the temperature and you must fix the aforementioned components by means of a special insulation kit.

Furthermore, the limiter is equipped with a safety thermostat, which opens the circuit if the critical temperature is reached.

Honeywell 2455R 82-195 L70C

The Green BMS limiter uses 12vdc power relays and it is recommended for charging currents not exceeding 20A

The Green BMS limiter is for 16s Lifepo4 48v: it could be used for higher voltage charging, but the voltage between the "IN" and "OUT" terminals must not exceed 10Vand in any case you must proceed with caution, verifying that the system is safe!

The electrical diagram of the limiter was created with the QElectroTech opensource CAD application.

All project files are available in the Github repository