What causes fault code VFD-BUS1 (VFD DC Bus Fault)?

Pre-charge resistor open — resistor burned out from excessive power cycling. DC bus contactor not pulling in — coil failed or aux contact feedback not received by control board. DC bus capacitors degraded — high ESR causing excessive ripple. Bus voltage sensing circuit fault on control board. Excessive power cycling causing pre-charge resistor thermal fatigue

How do I fix fault code VFD-BUS1?

CAUTION: DC bus capacitors store lethal voltage — wait 5 minutes after power off, then verify with meter before touching anything inside drive. Listen for DC bus contactor click when power is applied — should hear relay pull in after 1-2 seconds. Check pre-charge resistor with ohmmeter — compare to marked value (typically 10-100 ohm). Measure DC bus voltage — should charge to line voltage x 1.414 within 5 seconds of power-up. If bus voltage is unstable or shows excessive ripple, capacitors need replacement — this is a factory repair. Replace pre-charge resistor if open — use exact replacement rating

VFD DC Bus Fault

VFD-BUS1

DC bus charging circuit or bus capacitor bank fault detected. Pre-charge resistor or contactor malfunction.

critical vfd

vfd dc bus capacitor pre-charge contactor

Probable Causes (ranked)

Pre-charge resistor open — resistor burned out from excessive power cycling
DC bus contactor not pulling in — coil failed or aux contact feedback not received by control board
DC bus capacitors degraded — high ESR causing excessive ripple
Bus voltage sensing circuit fault on control board
Excessive power cycling causing pre-charge resistor thermal fatigue

Fix Steps

1 CAUTION: DC bus capacitors store lethal voltage — wait 5 minutes after power off, then verify with meter before touching anything inside drive
2 Listen for DC bus contactor click when power is applied — should hear relay pull in after 1-2 seconds
3 Check pre-charge resistor with ohmmeter — compare to marked value (typically 10-100 ohm)
4 Measure DC bus voltage — should charge to line voltage x 1.414 within 5 seconds of power-up
5 If bus voltage is unstable or shows excessive ripple, capacitors need replacement — this is a factory repair
6 Replace pre-charge resistor if open — use exact replacement rating

Field Trick

If a VFD keeps blowing pre-charge resistors, someone is cycling power too fast. Pre-charge resistors need 60 seconds between power cycles to cool. Put a time-delay relay in the control circuit to enforce a 60-second minimum off-time.

Suggested Replacement Parts

Parts matched to fault category: Vfd

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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