Beyond the protective functions, additional functions are possible in the BMS. These functions are less about safety and more about exploiting the maximum capacity and extending service life or the capacity indicator for the customer.
Cell balance is used in battery packs with more than one cell connected in series to keep the cells and the states of charge in a balanced condition. In particular, states of charge which arise due to different temperatures and internal resistances should be balanced by the cell balance. It prevents the battery pack from shutting down prematurely due to under or excess voltage of a cell, whereby the weakest cell determines the performance of the entire system.
In order to determine the capacity of the battery pack, a BMS has a gas gauge system. The gas gauge determines the overall capacity and the remaining capacity that is still available. It is certainly the most complex of the functions available. In order to be able to obtain the most precise results possible, it has to be developed to suit the application. Of particular relevance here are the current profile of the end-use application and the user‘s behaviour.
A bus system is available to the battery pack for reading the data. The most common bus systems are I2C, SMBus, CAN, LIN or RS232, whereby all other buses are also possible.
In low-power systems, it can make sense to integrate the charging unit for the battery pack into the BMS. This has the advantage that the charger in the event of a cell change can also be adjusted, thus always ensuring backwards compatibility to older systems.
In systems in which the battery is the central element, system functions can be transferred to the battery. This means a second form of intelligence (micro controller) in the system can be saved. For example, motor control and battery protection circuitry are unified in the battery. This does away with the control-related micro controller (μC) and the double configuration of the power FETs
(FET = Field-Effect Transistors).