Undervoltage

What does -USF mean?

This fault signifies that the input voltage to the drive controller has dropped below its minimum operating threshold or experienced a significant transient dip. A damaged pre-charge resistor or internal power supply issue could also prevent the DC bus from charging correctly. Operating with undervoltage can cause erratic drive behavior, prevent it from starting, or damage internal components over time.

Complete Troubleshooting Guide

1. 1

   Measure the incoming line voltage and confirm it is within the drive controller's specified operating range. Check for sags or brownouts on the supply.

2. 2

   Check for transient voltage dips or sags on the input power supply that might momentarily trigger this fault. Review power quality logs if available.

3. 3

   Verify the setting of the UnS (Nominal Supply Voltage) parameter to ensure it correctly matches the actual line voltage. If all external power supply checks pass, the drive controller may require replacement due to an internal component failure (e.g., pre-charge resistor).