How does the li-ion battery BMS work?

XTAR Light

Apr 26, 2010
If you want to DIY a Li-ion battery pack, to ensure its safety and longevity, you will need a reliable battery management system. The BMS is a set of electronics that monitors and manages all of the Li-ion batteries' performance. The important function of the BMS is to protect the batteries from damage caused by overcharging or over-discharging.

So how does the BMS work exactly? The BMS monitors individual cells in the battery pack. It can calculate how much the current safely goes in and comes out without damaging the battery. The current limits prevent the source and the load from overdrawing or overcharging the battery. This protects the battery pack from cell voltages getting too high or low, which helps increase the battery's longevity. The BMS also monitors the remaining charge in the battery. It continually tracks the amount of energy entering and exiting the battery pack and monitors cell voltages. It uses this data to know when the battery is drained and shut the battery down.

And the BMS ensures that each cell operates within the prescribed limits. If it is not the case, then it tries to solve the problem. For example, if the cells inside the battery pack are too hot, then the BMS manages the cooling system to reduce the battery pack's temperature. In case of variations in cell voltage, the BMS performs cell balancing. To balance the cells, it transfers energy from one cell to another to ensure that all cells operate at the same voltage level.