IndustrialDriveDataDrive Board & Diagnostic Database
Diagnostic workflow

PowerFlex F5 / F4 DC Bus Diagnostic Workflow

Entry symptom: PowerFlex trips on F5 DC bus overvoltage or F4 undervoltage during power-up, line sag, acceleration or deceleration.

Safety controls before proceeding
  • Input and DC-link measurements require qualified procedure.
  • Verify discharge before internal inspection.
  • Regenerative loads can move unexpectedly.

Investigation sequence

1

Split overvoltage from undervoltage

Record fault number and whether the event occurs on start, plant sag, steady run or deceleration.

2

Measure supply at drive

Measure input voltage at the drive terminals and compare under plant load changes.

3

Review DC bus behaviour

Use available display/diagnostic values to correlate DC bus with the event.

4

Check brake path for F5

Review decel ramp, load inertia, brake resistor, brake chopper and wiring where fitted.

5

Check input/precharge path for F4

Inspect fuses, contactor poles, loose terminals, precharge and DC-link evidence after line-side proof.

Stop conditions

  • Live measurement cannot be performed safely
  • Brake resistor overheats
  • One input phase is missing
  • DC bus discharge cannot be verified

Linked records

F5
DC Bus Overvoltage

The DC bus rose above its permitted boundary, usually from regenerated energy, high input line, short decel time, brake path failure or DC-bus measurement issue.

Open →F4
Undervoltage Fault

The DC bus or input supply is too low or unstable. The first route is line voltage, fuses/contactors, precharge, DC-link capacitors and supply sag evidence.

Open →Circuit
PowerFlex Input, DC Bus and Dynamic Brake Path

Routes F4 and F5 evidence through input phases, fuses/contactors, precharge, DC-link capacitors, brake chopper/resistor, load inertia and line voltage.

Open →