Battery Under Voltage

What does F74 mean?

This Manual Fault occurs when the DC bus voltage drops below the BMS reference discharge voltage. This indicates that the battery is either discharged beyond its safe operating limits or there is a connectivity issue on the DC bus.

• Battery pack discharged below its safe minimum operating voltage due to prolonged load or insufficient charging.
• High internal resistance within the battery pack due to aging, damage, or extreme temperature, causing excessive voltage sag under load.
• Faulty Battery Management System (BMS) voltage sensor providing erroneous low readings, triggering a false undervoltage fault.
• Communication loss between the inverter and the BMS, preventing accurate battery state reporting (e.g., CAN bus fault, timeout).
• Loose or corroded connections on the DC bus cables between the battery and the inverter, causing significant voltage drop under load.

Click steps to track your progress.

1. 1

   1. Disconnect the load and measure the open-circuit voltage of the entire battery pack directly at the battery terminals using a calibrated DC voltmeter.

2. 2

   2. Access the Battery Management System (BMS) diagnostics to check the reported battery voltage and individual cell voltages, comparing them to the inverter's displayed voltage.

3. 3

   3. Inspect all DC bus cable connections from the battery to the inverter for tightness, corrosion, and proper crimping.

4. 4

   4. Verify the battery's State of Charge (SOC) reported by the BMS or an external battery monitor, and initiate a controlled charge cycle if SOC is critically low.

5. 5

   5. Monitor the battery voltage while applying a known load and observe for excessive voltage drop, indicating high internal resistance (e.g., measure voltage drop at 0.5C discharge rate).