The LiFePO4 battery: preventing cell under voltage, over voltage and over temperature
The first line of protection is cell balancing. All Victron LiFePO4 batteries have integrated cell balancing.
The second line of protection consists of:
- shut down of the load in case of imminent cell under voltage, and
- shut down or reduction of the charging current in case of imminent cell over voltage, high temperature (>50°C) or low temperature (<0°C).
The VE.Bus BMS is the core of the second protection line.
However, not all loads or chargers can be controlled directly by the VE.Bus BMS.
In order to shut down such loads or chargers several VE.Bus BMS controllable Cyrix switches are available.
The Cyrix - Li -load will disengage when its control input becomes free floating.
If the battery voltage recovers after disconnection (which will happen when no other loads are connected to the battery), the output of the BMS will become high and the Cyrix will reengage after 30 seconds. After 3 attempts to reengage, the Cyrix will remain disengaged until battery voltage has increased to more than 13V (resp.26V or 52V) during at least 30 seconds (which is a sign that the battery is being recharged).