Common VFD Problems and When to Seek Professional Repair

Variable frequency drives (VFDs) control the speed of motors on pumps, fans, conveyors and process machinery. They save energy and improve control — but when one trips or fails, the equipment it drives usually stops.

This article covers the faults we see most often, what typically causes them and when it is time to call in professional repair.

Safety first: VFDs contain capacitors that can hold a dangerous charge after power is removed. Only qualified personnel should open a drive or work on its terminals, following the manufacturer's instructions and your site's isolation procedures.

Overcurrent trips

An overcurrent fault means the drive detected more current than it allows. Common causes include:

• Acceleration time set too short for the load
• Mechanical problems — a jammed pump, seized bearing or overloaded conveyor
• Motor or cable insulation faults
• Incorrect motor data in the drive parameters

What to check: whether the load turns freely, recent parameter changes and the condition of the motor and cable (by qualified staff). If the trip occurs immediately on start with no load, the drive's power section may be damaged.

Overvoltage trips

The DC bus voltage inside the drive rose too high. This often happens when:

• A high-inertia load decelerates faster than the drive can absorb the returned energy
• The supply voltage is high or has spikes
• A braking resistor is required but missing or faulty

What to check: deceleration time, braking arrangements and supply conditions.

Undervoltage trips

The DC bus fell too low, usually due to a supply dip, a loose or failed supply connection, or an internal problem in the drive's input stage.

Overheating

Drives derate or trip when internal temperature is too high. Typical reasons are:

• Failed or clogged cooling fans
• Dust-blocked heat sinks or panel filters
• Panel ventilation not sized for the drive's losses
• High ambient temperature

Fans are wear items. A drive that trips on temperature in summer but runs in winter is often telling you its cooling is marginal.

Ground (earth) faults

The drive detected current leaking to earth. This usually points to the motor or output cable — damaged insulation, moisture in a terminal box — but can also indicate an internal fault.

Drive doesn't power up

No display, no response. Causes range from a supply problem or blown input fuses to a failed internal power supply or control board. If the incoming supply is confirmed healthy, the drive needs diagnosis.

Communication faults

Drives controlled over a network can trip when communication with the PLC is lost — a loose connector, a damaged cable, incorrect addressing or a configuration change.

When to seek professional repair

Call for professional diagnosis when:

• The drive shows physical signs of damage — burning smell, discolouration, swollen components
• It trips immediately with the motor disconnected or uncoupled
• Fault codes return after the obvious external causes have been checked
• The drive doesn't power up with a healthy supply
• There has been a supply event such as lightning or a major voltage disturbance

Repair is often worth considering for higher-rated or older drives where replacement is costly or slow. For small or very old drives, replacement may be more sensible — a good repair partner will tell you which.

Reduce repeat failures

• Keep panel filters and drive heat sinks clean
• Check and replace cooling fans as part of maintenance
• Keep a parameter backup for every drive
• Investigate supply quality if several drives fail around the same time
• Verify that panel ventilation suits the installed drives

How Sparsh Automation can help

We provide VFD repair and refurbishment for drives from leading brands including Siemens, ABB, Schneider and Danfoss, along with drive supply and maintenance support. Share the drive model, rating and fault code through our enquiry form or call us.