Current control methods
Choosing the right way to let the BMS turn off the battery current
The method that allows the BMS to control the battery current depends on the battery topology and the devices connected to it.
This application note lists all combinations, and persents a recommended control method for each.
A battery pack may:
The system external to the battery may be:
These devices may:
A load may be:
Here it is assumed that a charger is only capable of charging (it is not bidirectional).
The BMS needs to control the charging and discharging current separately and independently. But the external device(s) and the battery topology may not be directly compatible with that requirement.
Therefore, some of these applications are straightforward, while others require somewhat complex circuits.
In this table, find the combination that describes your system, and note the recommended circuit number.
This table shows each circuit (listed in the table above) and gives some details about it.
The rectifier diodes and the contactors' contacts must be rated for the current they handle and for the full battery voltage. In circuits 3, 5 and 7, the contactor for the charger port only needs to be rated for the charger current, which may be less than the load current.
Note that each of the rectifier diodes will waste significant energy in heat whenever the contactor across it is open. That only occurs if only charging or only discharging is allowed; if both are allowed, then they generate no heat.
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