Variable Speed Drives are reliable when correctly installed and sized.
However, most faults are not caused by the drive itself — they are caused by incorrect selection, wiring issues, environmental factors or motor problems.
Understanding common fault conditions helps reduce downtime and prevent repeat failures.
Search faults or symptoms (e.g. “overcurrent”, “motor overheating”)
| Symptom | Possible Cause | Solution |
|---|---|---|
| Drive trips on start | Acceleration time too short | Increase ramp time |
| Motor overheating | Incorrect VFD sizing | Verify motor FLA and drive rating |
| Overcurrent fault | Mechanical load jam | Inspect load and bearings |
| Undervoltage fault | Supply drop | Check incoming supply |
Typical Causes:
- Motor Overload
- Acceleration Time Too Short
- Mechanical Jam
- Incorrect Drive Sizing
- Short Circuit in Motor Cable
Practical Checks:
- Compare motor FLA with drive rating
- Increase acceleration ramp timing
- Inspect mechanical load
- Measure motor winding resistance
Typical Causes:
- Rapid deceleration
- Not able to discharge overvoltage, requires braking resistor fitting
- Regenerative load (ie. loaded conveyor, vertical loads)
- Supply voltage fluctuations
Practical Checks:
- Increase deceleration time
- Install braking resistor
- Verify income supply voltage
Typical Causes:
- Weak mains supply
- Voltage dips
- Long cable runs
- Loose input connections
Practical Checks:
- Measure line voltage under load
- Check terminal torque
- Inspect upstream breaker and isolator
Typical Causes:
- Blocked or dirty ventilation filters
- High ambient temperature
- Inadequate enclosure size
- Check enclosure IP rating
Practical Checks:
- Clean cooling fins/fans
- Verify panel ventilation
- Check enclosure IP rating
Typical Causes:
- Damaged motor cable
- Moisture ingress
- Insulation breakdown
- Incorrect earthing
Practical Checks:
- Insulation resistance test (megger)
- Inspect cable terminations
- Check motor condition
Typical Symptoms:
- Motor Overheating
- Motor not reaching speed
- Motor vibration
- Motor humming but not turning
Practical Checks:
- Ensure proper cooling when running motor a low speeds
- Increase acceleration ramp timing
- Inspect mechanical load
- Measure motor winding resistance
When to Consider Replacing a Drive
Replacement may be required when:
- Drive repeatedly trips under normal load
- Internal power module failure occurs
- Age exceeds typical service life (7-10years industrial use)
- Parts are absolute
Correct replacement selection must be based on motor current and application duty — not simply matching kW rating.
Practical Recommendation
Before replacing a failed drive:
- Record the fault code
- Confirm motor Nameplate current
- Confirm supply voltage
- Identify application type
Correct selection makes a major difference.
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