What causes fault code VFD-BF1 (VFD Bus Fault)?

Pre-charge resistor open — bus cannot charge through soft-start circuit. Bus capacitors failed — swollen tops, leaking electrolyte. Bus charging relay/contactor stuck open. Internal fuse blown on DC bus. Power supply board failure

How do I fix fault code VFD-BF1?

Power down completely, wait 5 min for caps to discharge. Measure DC bus voltage at test points — should be ~1.35x line voltage. Inspect capacitors visually — look for bulging tops or leakage. Check pre-charge resistor with ohmmeter — compare to spec. Listen for charging relay click on power-up. If bus won't charge, drive likely needs factory repair or replacement

VFD Bus Fault

VFD-BF1

Internal DC bus fault detected. Bus charging circuit, capacitors, or pre-charge resistor may have failed.

critical vfd

vfd bus fault capacitor pre-charge dc bus

Probable Causes (ranked)

Pre-charge resistor open — bus cannot charge through soft-start circuit
Bus capacitors failed — swollen tops, leaking electrolyte
Bus charging relay/contactor stuck open
Internal fuse blown on DC bus
Power supply board failure

Fix Steps

1 Power down completely, wait 5 min for caps to discharge
2 Measure DC bus voltage at test points — should be ~1.35x line voltage
3 Inspect capacitors visually — look for bulging tops or leakage
4 Check pre-charge resistor with ohmmeter — compare to spec
5 Listen for charging relay click on power-up
6 If bus won't charge, drive likely needs factory repair or replacement

Field Trick

After full power-down and discharge, measure DC bus at the test points. If it reads zero or very low when powered up, the pre-charge circuit is dead.

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.

Need a deeper diagnosis with photo analysis and AI-powered troubleshooting?

Run Full Diagnosis