What is a DC rated battery circuit breaker (BCB)?

The DC rated Battery Circuit Breaker (BCB) provides still overcurrent protection, if correctly coordinated, even though it is not as fast as the fuses. These breakers must be set at a safe intervention value based on the battery short circuit current.

What is a short circuit current in a battery?

Battery manufacturers provide a value of short circuit current which needs to be used for validation of proper protection device. Duration of this short circuit current can be of few seconds before a battery failure occurs. The characteristic current and duration changes depending on the battery type.

How a battery protection device should be sized?

A protection device must be sized properly so that the energy flowing from the batteries during the failure will not cause damage to the batteries or other components along the short circuit path. The protection must clear the fault in less than 100 milliseconds. The impedance of the line is mainly resistance and inductance.

What factors affect the fault current in a battery?

Parameters that influence the Fault current The Open Circuit Voltage (OCV). The internal battery parameters are strongly dependent by the state of charge and the aging of the battery. The OCV decreases and the internal impedance of the battery increases as the battery is discharged or as it gets older.

Can a protection device trip a battery?

The selected protection device must trip in case of a fault in less than 100 ms. In case the fault current provided by the battery does not allow for the finding of protection devices, such as a Circuit Breaker or fuse, that meets the derating criteria stated in point B, it is hence possible to increase the multiplier up to 0.7.

What is the short circuit current of a VRLA battery?

Example: For the VRLA type battery close to the End of Discharge (EOD) and End of Life (EOL), due the OCV reduction and resistance increase, the short circuit current can be around 60% of the nominal short circuit current.