Lithium Battery Management System

Randy Anderson, National Technical Sales & Training Manager

Our on going topic has been lithium battery packs and today we're going to talk about the Battery Management System.

The Battery Management System in a Lithium battery pack is key to proper performance. Unlike lead acid batteries, where the external charger controls the voltage and amperage going into the pack and determines when charging should be terminated, the BMS performs this function. The BMS in the system controls and monitors the voltage, amperage and temperature of each individual cell in the pack. During charge, the BMS will reduce the charge rate to an individual cell. If temperatures start to get out of parameter it will redirect the charge current to other cells in the pack until the cells are balanced. The BMS also provides a level of safety protection in the pack as it fuses the individual cells as well as the main circuit to prevent any short circuits.

Like we mentioned above, one of the purposes or functions of the BMS is to monitor voltage, amperage, temperature and stated charge of all the individual cells in the pack. So whether there's 4 cells or 400 cells in the pack, the job of the BMS is to monitor the parameters of all those cells. Another function of the BMS is charge rate and balancing. So the BMS will control the amount of charge that goes into the cells. So in a traditional charger, if we're charging lead acid batteries let's say, the charger itself controls the function of how much amperage and voltage goes into the pack. Whereas in a lithium pack, the BMS provides that function.

So it will determine how much amperage and voltage goes to the individual cells, and it will balance those out amongst all the cells.

The other purpose is to redirect the current. So again, during charge, if a cell is getting warm, or the state of charge is getting higher than other cells, it will balance that out by redirecting the current to other cells that are of a lower state of charge.

And the final thing is, the BMS provides protection for over and under voltage, over and under temperature, and over current. So it's fused on several different levels to protect the pack should there be any shorts or issues like that, and to stop any thermal events.

For any questions on lithium, or any other battery technologies, feel free to contact us!

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