VE.Bus BMS V2

Lithium batteries are expensive and can be damaged due to over discharge or over charge. Damage due to over discharge can occur if small loads (such as: alarm systems, relays, standby current of certain loads, back current drain of battery chargers or charge regulators) slowly discharge the battery when the system is not in use. In case of any doubt about possible residual current draw, isolate the battery by opening the battery switch, pulling the battery fuse(s) or disconnecting the battery plus when the system is not in use.

A residual discharge current is especially dangerous if the system has been discharged completely and a low cell voltage shutdown has occurred. After shutdown due to low cell voltage, a capacity reserve of approximately 1Ah per 100Ah battery capacity is left in the battery. The battery will be damaged if the remaining capacity reserve is drawn from the battery. A residual current of 10mA for example may damage a 200Ah battery if the system is left in discharged state for more than 8 days.

The shutdown due to low cell voltage by the BMS should always be used as a last resort to be on the safe side at all times. We recommend not letting it get that far in the first place and instead shutting down the system automatically based on a defined state of charge so that there is enough reserve capacity in the battery. For an inverter/charger, for example, this can be done via the VE.Configure setting 'shut-down on SoC'. It is even easier with a BMV, whose relay can control the remote on/off port of the BMS via an adjustable SoC value.