DC Bus Undervoltage

What does Uv1 mean?

This fault occurs due to a phase loss in the drive's input power, loose input wiring, excessive fluctuations or loss of input power, or degraded main circuit capacitors or soft-charge bypass relays. The drive detects this when the DC bus voltage falls below a critical level (e.g., 190V for 200V class, 380V for 400V class) while running. Sustained undervoltage can cause erratic drive behavior or complete shutdown.

• Internal DC bus voltage falls below the acceptable minimum threshold (P1-01).
• Loss of incoming AC power during operation.
• Faulty power supply or rectifier stage.
• Overloading the drive during startup.

Click steps to track your progress.

1. 1

   Inspect and correct any errors in the wiring of the main circuit drive input power, ensuring all phases are present.

2. 2

   Tighten all input power terminal screws to their specified torque to eliminate loose connections.

3. 3

   Examine the input power supply for stability issues or voltage drops; replace or upgrade the power supply if inadequate, and check the main circuit magnetic contactor.

4. 4

   Monitor U4-05 [CapacitorMaintenance] and U4-06 [PreChargeRelayMainte]; if either is above 90%, contact Yaskawa to replace the control board or the entire drive.

5. 5

   Perform a Fault Reset to clear the fault once power supply and hardware integrity are confirmed.