Every Felicity Solar lithium battery has a BMS that watches each cell, the pack current and the temperatures. When something goes outside its limits, it first raises a warning, then, if the situation continues, it protects the battery by stopping the charge or the discharge. The inverter rarely tells you which one happened or why; it usually shows a generic battery fault.
Warning versus protection
- Warning: a value is approaching its limit. Nothing is cut yet. The BMS is telling you to pay attention.
- Protection: the limit has been reached. The BMS opens its switches for charge, discharge or both, to keep the cells safe. It releases them once conditions are back to normal.
A protection is not a failure. It is the BMS doing its job. What matters is how often it happens and why.
The usual suspects
| Alarm family | Typical cause | First check |
|---|---|---|
| Cell over-voltage | One cell reaches full before the others; charge voltage set too high | Cell spread at the end of charge; inverter charge voltage |
| Cell under-voltage | Battery deeply discharged; one weak cell ending the discharge early | Inverter cut-off level; lowest cell at the end of the night |
| Charge over-current | Inverter or generator charging faster than the battery allows | Maximum charge current in the inverter settings |
| Discharge over-current | Large loads starting together; battery bank too small for the load | Peak loads; number of batteries in parallel |
| Over-temperature | Hot room, poor ventilation, high current for a long time | Location of the battery; airflow around it |
| Under-temperature | Cold location; charging blocked near freezing | Room temperature in winter |
| Communication fault | Loose or wrong communication cable, address conflict | Cable and address settings, before suspecting the battery |
Reading the pattern
One protection on a cold morning or during a heavy load is not a concern. Repeated ones are information:
- Over-voltage protection at the end of every charge usually points to cell imbalance. A longer time at full charge, or a slightly lower charge voltage, often solves it.
- Under-voltage protection while the displayed charge is still above 10 % suggests the charge estimate has drifted, or that one cell has less capacity than the others.
- Discharge over-current when the oven and the kettle run together means the bank is at its limit for that load; staggering the loads or adding a battery helps.
Seeing the alarm, not just the fault light
Felicity Monitor reads the BMS over RS485 and shows the warnings and protections in plain words, along with the cell voltages and temperatures at the same moment, so the cause is usually obvious. On the free Cloud you can set an e-mail alert for any BMS alarm, and the history tells you whether it was a one-off or the third time this week. The box only reads: it never changes a setting on the battery or the inverter.