Undervoltage fault

What does F9 mean?

The DC-link voltage has dropped below acceptable limits, potentially triggering an undervoltage control supervision (S3). This could be caused by a low supply voltage, an internal frequency converter fault, a broken input fuse, or an open external charge switch. Prolonged undervoltage can cause erratic drive behavior and component stress.

• Input supply voltage dropping below the drive's minimum operating threshold (e.g., brownout condition, utility sag).
• Loose or corroded connections in the input power circuit (e.g., main contactor, fuses, input terminals L1, L2, L3).
• Blown input fuses or tripped input circuit breaker, leading to a complete loss of one or more input phases.
• Over-sized input line reactor or input filter causing an excessive voltage drop under load.
• Internal power supply or DC-link capacitor bank degradation within the drive.

Click steps to track your progress.

1. 1

   Measure the incoming line voltage at the drive input terminals (L1, L2, L3) using a true RMS voltmeter. Verify each phase-to-phase and phase-to-ground voltage is within the drive's specified range (e.g., 400V ±10%).

2. 2

   Inspect all input power connections (terminal block, main contactor, fuses) for tightness and signs of overheating or corrosion. Torque connections to specified values.

3. 3

   Check continuity and rating of all input fuses using a multimeter (ohmmeter). Replace any blown fuses with the correct type and rating.

4. 4

   Verify the input line reactor or filter impedance matches the drive's current rating and specifications. Remove temporarily if possible to test.

5. 5

   Monitor the DC-link voltage from the drive's display (e.g., Menu 1-10 'DC-link voltage') while the drive is attempting to operate. Compare to expected values (e.g., ~1.35 * U_line).