Battery Management Systems (BMS)

Or why you should probably pay a bit more

What are BMS?

A BMS (Battery Managment System) is any electronic system that manages a rechargeable battery usually consisting of a number of cells in either parallel or serial configuration, or both. The BMS protects the battery from operating outside its safe operating conditions, monitors its state, and possibly also balances the cells. A BMS monitors and controls parameters like voltage of the individual cells / cell packs, temperature of the pack, charge and discharge current, state of balance of the cells and it might also monitor the health of the cells.

Lithium batteries consist of battery packs built together with a BMS, more advanced ones with an external communication data interface are called smart BMS.

Different types of BMS

Parameters monitored and controlled

A BMS may calculate the following values:

  • Voltage: the voltage of each cell block
  • State of charge (SoC) or depth of discharge (DoD), to indicate the charge level of the battery
  • State of health (SoH), a defined measurement of the remaining capacity of the used battery as % of the original capacity of a new cell
  • State of power (SoP), the amount of power available for a defined time interval given the current power usage, temperature and other conditions
  • State of Safety (SOS)
  • Maximum charge current as charge current limit (CCL)
  • Maximum discharge current as a discharge current limit (DCL)
  • Energy [kWh] delivered since last charge or charge cycle
  • Internal impedance of a cell (to determine open circuit voltage)
  • Charge [Ah] delivered or stored
  • Total operating time since first use
  • Total number of cycles
  • Temperature
  • Coolant flow for air or liquid cooled batteries



After many uncertainties with other BMS and reading

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