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.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 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.

2. 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.

3. 5

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