How to build a BMS for DIY battery packs effectively?

Choosing the Right Components

When selecting components for your BMS, consider the battery’s voltage, current, and capacity. For a 12V, 50Ah EV battery pack, use a high-side MOSFET like the IRF9640, which can handle up to 60A of current. For the shunt resistor, choose a 0.1Ω, 50W resistor, such as the VPG SMDR-0.1R-50, which can accurately measure the current. The microcontroller should be able to handle the voltage and current measurements, and have enough memory to store the data.

Implementing the Charge/Discharge Control Strategy

Implement a charge/discharge control strategy, such as the CC-CV method, to regulate the battery’s charge and discharge cycles. In this method, the charger applies a constant current (CC) until the battery reaches a set voltage (CV), and then switches to a constant voltage mode to top off the battery. You can use a simple voltage divider to measure the battery voltage and a current transformer to measure the current. The microcontroller can then adjust the charger’s output accordingly.

Setting Up the Protection Circuits

Set up protection circuits to prevent overcharge, overdischarge, and short-circuit conditions. For overcharge protection, use a voltage comparator to detect when the battery voltage exceeds a set threshold. For overdischarge protection, use a current comparator to detect when the battery current drops below a set threshold. For short-circuit protection, use a fuse or a crowbar circuit to disconnect the battery from the circuit when a short circuit occurs.