What causes fault code VFD-UV1 (VFD DC Bus Undervoltage)?

Incoming power sag or brownout — facility-wide voltage dip. Loose connection on input power terminals — arcing causes intermittent drops. Input fuses partially blown — one phase open. Contactor feeding drive has bad contact — check all 3 phases with meter. DC bus capacitors degrading — cannot hold voltage during transients

How do I fix fault code VFD-UV1?

Measure voltage at drive input terminals under load — all 3 phases within 3%. Tighten all input power connections — check torque specs on terminal blocks. Check input fuses with continuity test, not just visual inspection. Verify contactor contacts — measure voltage drop across each pole under load. If DC bus caps are swollen or leaking, drive needs repair/replacement. Add ride-through feature if available in drive parameters. Consider adding a line reactor on input to improve power quality

VFD DC Bus Undervoltage

VFD-UV1

DC bus voltage dropped below minimum operating threshold. Drive cannot maintain output to motor.

medium vfd conveyor packaging

vfd undervoltage dc bus power quality brownout

Probable Causes (ranked)

Incoming power sag or brownout — facility-wide voltage dip
Loose connection on input power terminals — arcing causes intermittent drops
Input fuses partially blown — one phase open
Contactor feeding drive has bad contact — check all 3 phases with meter
DC bus capacitors degrading — cannot hold voltage during transients

Fix Steps

1 Measure voltage at drive input terminals under load — all 3 phases within 3%
2 Tighten all input power connections — check torque specs on terminal blocks
3 Check input fuses with continuity test, not just visual inspection
4 Verify contactor contacts — measure voltage drop across each pole under load
5 If DC bus caps are swollen or leaking, drive needs repair/replacement
6 Add ride-through feature if available in drive parameters
7 Consider adding a line reactor on input to improve power quality

Field Trick

Put your meter on the drive input terminals and watch for voltage sag when nearby big motors start. If it dips >15%, that's your UV source.

Suggested Replacement Parts

Parts matched to fault category: Vfd Drive

Allen-Bradley PowerFlex 525 AC Drive 1HP P/N: 25B-D2P3N114 1HP, 480V, 3-phase, built-in EtherNet/IP, EMC filter

AutomationDirect $395.00 Amazon $450.00 Grainger $520.00

ABB ACS580 General Purpose Drive 2HP P/N: ACS580-01-05A7-4 2HP, 480V, built-in safe torque off, adaptive programming

AutomationDirect $425.00 Amazon $480.00 Grainger $550.00

GS20 AC Drive 1HP (Budget Option) P/N: GS20-20P5 1HP, 230V, sensorless vector, compact size — good replacement for testing

AutomationDirect $149.00 Amazon $175.00

Prices are estimates. Verify part numbers match your equipment before ordering.

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