Undervoltage

What does 9 mean?

The DC-link voltage has fallen below its acceptable operating limits. This can be caused by a low incoming supply voltage, a defective input fuse, an external charge switch failing to close, or an internal AC drive fault. Prolonged undervoltage can cause erratic drive behavior, prevent proper starting, and potentially stress internal components.

• Incoming AC supply voltage dropping below the drive's minimum operating threshold (e.g., 340V for a 400V drive).
• Blown or tripped input fuse/circuit breaker on one or more phases of the AC supply to the drive.
• Failure of the external main contactor or input disconnect switch to close, or intermittent connection.
• Defective internal power supply within the drive that generates DC-link voltage.
• Sudden, heavy load demand causing excessive current draw and voltage sag on the supply network.

Click steps to track your progress.

1. 1

   Measure the incoming AC supply voltage at the drive input terminals (L1, L2, L3) with a true RMS multimeter, confirming it is above the minimum specified voltage (e.g., 340V).

2. 2

   Verify continuity of all input fuses or proper operation of input circuit breakers using a multimeter's resistance setting.

3. 3

   Check the control voltage to the external main contactor (if present) to ensure it is energizing correctly and its auxiliary contacts are closing.

4. 4

   Measure the DC-link voltage (e.g., terminals DC+ and DC-) using a DC voltmeter during power-up and operation, comparing it to the expected rectified voltage.

5. 5

   Inspect the drive's internal wiring and connections to the rectifier bridge for any loose terminals or signs of arcing.