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Troubleshooting GuideVariable Frequency Drive Faulting
Write down the fault code — it cuts diagnosis time in half.
What the fault code tells you
A VFD constantly measures current, voltage and temperature to protect itself and the motor. When a limit is exceeded it cuts the output and displays a code showing which limit was exceeded.
The code is a sign of which group the fault belongs to, not the fault itself. An overcurrent fault, for example, does not mean the VFD is broken — most of the time there is a mechanical strain somewhere.
Possible causes
| Fault group | Typical cause | Check first |
|---|---|---|
| Overcurrent | Brake releases late, mechanical friction, overload | Brake timing, load, mechanical freedom of movement |
| Overvoltage | Regenerative energy from deceleration cannot be dissipated | Braking resistor/unit, deceleration ramp |
| Overtemperature | Insufficient panel cooling | Fan, filter, ambient temperature |
| Ground/short circuit | Motor or cable insulation problem | Insulation measurement |
| Phase loss | Supply or contactor problem | Input phases, contactor contacts |
| Parameter | Settings lost or changed incorrectly | Compare with the backup |
| Communication | Cable, screen grounding, interference | Cable routing and screening |
Step-by-step diagnosis
- Write down the fault codeNote the code and the moment it occurred (on start-up or during deceleration).
- Determine when it happensLoaded or unloaded, during which motion — as important as the code.
- Check mechanical freedom of movementDoes the brake release fully, is anything binding.
- Measure panel temperatureIs the fan running, is the filter clogged.
- Measure supply voltagePhase voltages and imbalance.
- Compare the parametersCompare with the backup; create one if it does not exist.
- TestRun unloaded then with a stepped load and watch whether the code repeats.
Preventing a repeat
Most VFD faults recur for two reasons: panel environment and brake timing. In a dusty environment the filter clogs, internal temperature rises, and the same fault returns shortly after.
If the brake opens before the motor produces torque, or closes before the motor has stopped, both the VFD and the brake are strained. This timing is set during commissioning and is the point most often skipped in modernisation work.
Taking a parameter backup is the cheapest insurance: if a card needs replacing, the crane is back up in minutes rather than hours.
Technical terms
| Term | What it means |
|---|---|
| Regenerative energy | The energy the motor produces and feeds back during deceleration. |
| Braking resistor | The resistor that converts regenerative energy into heat. |
| Ramp time | The set time for acceleration or deceleration. |
| Parameter backup | A copy of the VFD's settings. |
Frequently asked questions
Can I just reset the VFD and carry on?
You can try it once, but if the fault repeats there is a real underlying cause. Resetting repeatedly amounts to disabling the protection system.
How do I take a parameter backup?
On most VFDs the settings can be exported via the keypad or software. Taking and storing this backup should be standard practice during commissioning.