Do you know the warning signs your soft starter or VSD needs servicing? Soft starters and variable speed drives (VSDs) are built to work hard for years, often in plant rooms, pump stations and factory floors where nobody pays them much attention until something goes wrong. But they rarely fail without warning. In most cases there are signs well before a breakdown: a unit running hotter than usual, a trip that keeps coming back, a start that sounds rougher than it used to.
Spotting those symptoms early gives you the chance to service or repair the equipment on your terms, rather than dealing with an unplanned shutdown. Here are the warning signs to look out for, what they might mean and what to do next.
1. Overheating
Heat is the biggest enemy of power electronics. Soft starters and drives contain semiconductors, capacitors and control boards that age much faster when they run hot, so overheating is often the first sign of trouble.
Look for over-temperature alarms or fault codes, enclosures that feel much hotter than normal, or the unit reducing output or tripping on warm days. Common causes include blocked heatsinks and filters, failed cooling fans, dust build-up, poor ventilation in the panel or plant room and a motor load that has increased over time.
Overheating is often straightforward to fix at an early stage. Cleaning, replacing filters or fans, and improving ventilation can restore normal operation. Left unchecked, it can lead to permanent damage to the power components.
2. Nuisance tripping
A soft starter or drive that trips occasionally for a clear reason is doing its job. One that trips repeatedly, especially without an obvious cause, is telling you something needs attention.
Frequent overcurrent, overvoltage, undervoltage or earth fault trips can point to a range of issues: loose or corroded connections, supply problems, deteriorating motor insulation, incorrect parameter settings, or failing internal components. In VSDs, repeated overvoltage trips during deceleration can also indicate the ramp-down time is too short for the load or that braking components need checking.
It’s tempting to simply reset and carry on, but repeated trips put stress on both the drive and the motor. Recording when trips happen and what the fault code says, helps an engineer find the root cause quickly.
3. Noisy or rough starts
A soft starter exists to bring the motor up to speed smoothly. If starts become jerky, noisy or slower than usual, something has changed.
Signs include clunking or banging as the motor starts, the motor struggling to reach full speed, a louder hum than normal, or mechanical shock through belts, couplings and pipework. Possible causes include failing thyristors, an issue with the bypass contactor, incorrect start settings, or a change in the load such as a worn pump or seized bearing.
In a VSD, unusual whining, buzzing or motor noise at particular speeds can indicate parameter issues, cable problems or motor bearing wear, some of which can be caused or worsened by the drive itself.
4. Erratic speed or poor control
With a drive, the whole point is precise speed control. If the motor hunts up and down, fails to follow its speed reference, or responds slowly to changes in demand, the drive or its control signals may need attention.
This can be caused by faulty sensors or wiring, electrical noise on control cables, incorrect tuning, or internal faults in the drive. In pumping and HVAC systems, erratic control can show up as unstable pressure, flow or temperature, and higher energy use.
5. Burning smells, discolouration or visible damage
Any burning smell from a soft starter, drive or panel should be treated seriously. Isolate the equipment safely and get it inspected.
During routine checks, a qualified person may also spot discoloured terminals, scorched cables, bulging or leaking capacitors, or signs of arcing. These usually indicate overheating, loose connections or component failure and they need prompt attention before they lead to a more serious fault.
6. Contactor chatter and bypass problems
Many soft starters use a bypass contactor that takes over once the motor is up to speed. If you hear chattering, buzzing or repeated clicking from the starter, or the unit trips at the changeover point, the contactor or its control circuit may be failing.
7. Age and running hours
Sometimes the warning sign is simply time. Components such as cooling fans and DC bus capacitors have a limited life and many manufacturers recommend replacing them at set intervals. A drive that has run continuously for many years may be due a service even if it seems healthy.
If a unit has been sitting unused for a long period, it’s also worth having it checked before bringing it back into service, as capacitors can degrade in storage.
Why regular servicing pays off
If you have seen the warning signs your soft starter or VSD needs servicing, a planned service costs far less than an emergency breakdown. Routine maintenance typically includes cleaning, checking and tightening connections, inspecting fans and filters, reviewing fault logs, checking parameter settings, and testing key components. It helps you spot problems early, extend equipment life and keep energy efficiency where it should be.
It also gives you control over timing. Instead of losing a critical pump or fan at the worst moment, you can schedule work for a quieter period.
Keep running while servicing happens
The challenge with servicing critical equipment is downtime. Taking a soft starter or drive offline can mean stopping a pump, a ventilation system or a production line.
Hiring a temporary soft starter or VSD solves that problem. A hire unit can run your motor while your own equipment is serviced, repaired or replaced, so your process keeps going. And if a warning sign turns into a failure before you’ve had chance to act, emergency hire can get you running again quickly while the fix is arranged.
If your soft starter or drive is showing any of these warning signs, get in touch with our team to discuss servicing support and temporary hire options.
Written by Neil Parsons, Technical Director – With over 35 years in electrical engineering across various sectors, these articles are written by a specialist with hands-on experience in electrical design and commissioning, PLC and variable speed drive programming and installation.
Frequently Asked Questions
How often should a soft starter or VSD be serviced?
It depends on the manufacturer’s guidance, the operating environment and how critical the equipment is. Units in dusty, hot or heavily used applications usually need attention more often. Many sites include drives and starters in an annual maintenance schedule as a minimum.
Why does my VSD keep tripping on overvoltage?
Overvoltage trips often happen during deceleration, when the motor feeds energy back into the drive. A deceleration time that is too short, braking component issues or supply problems are common causes. An engineer can review settings and fault logs to confirm.
Can a dirty drive really cause it to fail?
Yes. Dust and dirt block heatsinks and filters, reducing cooling. Over time, higher operating temperatures shorten component life and can cause overheating faults or failure.
Is it safe to keep resetting a tripped soft starter?
Repeated resets without finding the cause can damage the starter and the motor. Note the fault code and when the trip occurs, then have the equipment checked.
What does a noisy start mean on a soft starter?
It can indicate failing internal components, bypass contactor problems, incorrect settings or a mechanical issue with the driven load. It’s worth investigating before it leads to a breakdown.
Can I keep my motor running while my drive is serviced?
Yes. Hiring a temporary soft starter or VSD lets your motor keep running while your own unit is serviced, repaired or replaced.
What should I do if my drive smells of burning?
Safely isolate the equipment and have it inspected by a qualified engineer before using it again.
