What causes fault code VFD-DRF1 (VFD DC Bus Ripple Fault)?

Input phase lost — single-phasing causes excessive ripple. Bus capacitors losing capacitance — aging electrolytic caps. Input diode bridge rectifier has an open diode. Power supply harmonic interference

How do I fix fault code VFD-DRF1?

Check all 3 input phases with meter — voltage should be balanced within 3%. Measure DC bus voltage — should be stable ~1.35x line voltage, not pulsing. Check bus capacitor ESR if test equipment available. Test input diodes with diode check — all 6 diodes should show ~0.5V drop. If bus caps swollen or leaking, drive needs repair

VFD DC Bus Ripple Fault

VFD-DRF1

Excessive DC bus voltage ripple detected. Input rectifier or bus capacitors may be degrading.

high vfd

vfd dc bus ripple capacitor rectifier

Probable Causes (ranked)

Input phase lost — single-phasing causes excessive ripple
Bus capacitors losing capacitance — aging electrolytic caps
Input diode bridge rectifier has an open diode
Power supply harmonic interference

Fix Steps

1 Check all 3 input phases with meter — voltage should be balanced within 3%
2 Measure DC bus voltage — should be stable ~1.35x line voltage, not pulsing
3 Check bus capacitor ESR if test equipment available
4 Test input diodes with diode check — all 6 diodes should show ~0.5V drop
5 If bus caps swollen or leaking, drive needs repair

Field Trick

DC bus should be FLAT. If your scope shows 360Hz ripple, you've lost a capacitor. If 120Hz ripple, you've lost an input phase or diode.

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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