When people think about drives failing due to weather, they tend to think about winter. Cold starts, condensation, lubricant thickening in enclosed spaces. But ask any drive repair engineer about their busiest periods and the answer is when there has been extreme weather, especially July and August.
Summer heat is the single biggest environmental cause of inverter drive failure, and it kills drives in ways that are entirely preventable. The problem is that most maintenance teams do not connect the two things until they are already dealing with an unplanned shutdown.
Why Heat Is an Inverter Drive’s Biggest Enemy
Inverter drives generate substantial heat during normal operation. The power electronics inside, the IGBT modules, gate driver boards, and DC bus capacitors, all produce heat as a by-product of switching and converting power. Under normal ambient conditions, the drive’s internal cooling system manages this efficiently. When ambient temperatures rise significantly in summer, as they do inside plant rooms, machine enclosures, and poorly ventilated control panels, the thermal balance shifts.
Most standard industrial drives are rated to a maximum ambient of 40 or 50 degrees C. Beyond that, the drive must reduce its output current to protect its components, or it will trip on high temperature faults. In practice, plant rooms and enclosed machinery spaces regularly exceed these thresholds during British heatwaves, which have become both more frequent and more severe in recent years.
What Actually Fails and Why
The components most vulnerable to sustained heat stress are the DC bus capacitors and the IGBT power modules.
Electrolytic capacitors have a finite service life that is heavily influenced by temperature. The industry rule of thumb is that every 10 degree C rise in operating temperature halves the capacitor’s service life. A capacitor rated for 2,000 hours at 85 degrees C may only deliver 500 hours if it runs consistently at 105 degrees C due to elevated ambient and poor cooling. Over several summers of this, the capacitors degrade. Their capacitance drops, their equivalent series resistance rises, and eventually they fail, often without warning.
IGBTs and their associated gate driver circuitry are similarly vulnerable. IGBTs are thermally cycled every time the drive starts, stops or changes load. Under normal conditions, the thermal management system keeps junction temperatures within safe limits. Under high ambient conditions, the thermal headroom is reduced. A drive that runs perfectly all winter may start tripping on overcurrent or overtemperature faults every hot afternoon in July, not because anything has broken, but because the thermal margins have narrowed to the point where normal load transients tip the drive into fault.
Thermal Derating: What It Means in Practice
Most drive manufacturers publish derating curves in their technical documentation. These curves show how much the drive’s rated output current must be reduced as ambient temperature increases beyond the rated maximum. A drive rated at 32A output at 40 degrees C ambient might only deliver 25A continuously at 50 degrees C.
In practice, this matters enormously in applications where drives run at or near their rated current. A conveyor drive running at 28A in winter may be exceeding its thermally derated limit on a hot day, even though nothing has changed in the process itself. The drive trips. The site calls out a maintenance engineer. Nothing obvious is found. The drive runs fine for a few days, then trips again when the weather turns hot.
This pattern, intermittent trips on hot days with no obvious fault code pointing to a hardware failure, is one of the most common presentations we see from drives sent in over the summer months. The drive itself is often not damaged. But the repeated trips add stress to the capacitors and IGBTs that accumulates over time.
The Cooling Fan Problem
Every fan-cooled inverter drive has at least one cooling fan, and often several. These fans are the first line of defence against overheating, and they are also one of the most commonly neglected components in any maintenance schedule.
Cooling fans accumulate dust, debris, and fibres over time. In many industrial environments this build-up is rapid. A fan that is half blocked by debris may deliver a fraction of its rated airflow, turning the drive enclosure into a heat trap. Most drive manufacturers specify a minimum fan service interval of six to twelve months. Very few sites adhere to this in practice.
The other issue is fan bearing wear. Cooling fans in industrial drives are typically small, high-speed units that run continuously. Their bearings wear, their blades can become unbalanced, and their airflow reduces well before they visibly fail. A fan running at 60 per cent of its rated speed due to worn bearings may still appear to be working when you look at it, but it is not providing adequate cooling.
We have seen drives come in on the back of summer failure investigations where the root cause is simply a cooling fan that has been running at reduced capacity for years. Clean the fans, replace the worn bearing, and the drive runs through the following summer without issue.
What You Can Do Before the Temperature Rises
The good news is that heat-related drive failures are largely preventable with straightforward maintenance steps.
- Inspect and clean cooling fans and heat sink fins before the warm months. Remove accumulated dust, particularly from the heat sink fins, which can become completely blocked in dirty environments. A can of compressed air and ten minutes of time can meaningfully extend a drive’s service life.
- Check the ventilation of any enclosure or panel housing your drives. Enclosures need adequate airflow to dissipate the heat drives’ produce. Blocked cable entry points, inadequate ventilation holes, or cabinets placed in direct sunlight can push internal temperatures well beyond the drive’s rated limits.
- Review your drives’ ambient temperature ratings against the actual peak temperatures in the spaces where they are installed. If your plant room regularly reaches 45 degrees C on a hot day and your drives are rated to 40 degrees C, cleaning alone will not solve the problem.
- Consider having older drives serviced before summer rather than after a failure. Replacing degraded capacitors and checking thermal compound on IGBT heat sinks in spring is significantly cheaper than emergency repair and downtime in August.
When the Summer Failure Pattern Becomes Something More Serious
Intermittent heat-related trips are manageable. The more serious scenario is when a drive that has been running hot for several summers finally reaches a hard failure. By that point, the capacitors have degraded significantly, the thermal compound on the IGBTs has dried and cracked, and one hot afternoon pushes the drive into a fault it cannot recover from.
These drives tend to present with multiple simultaneous issues when they arrive for repair, partly because the root cause has been slowly building for years rather than arriving as a single event. The cost of repair is higher, the turnaround takes longer, and the risk of collateral damage to other components is greater than it would have been had the underlying thermal issues been addressed earlier.
The straightforward lesson is that heat management is maintenance, not a luxury. Treating it as such before the summer months is always cheaper than the alternative.
Need Expert Help with a Drive That Has Been Struggling in the Heat?
If you have a drive that has been tripping intermittently on hot days, or one that has failed outright during a warm period, it is worth getting a specialist assessment. Heat-related failures often involve capacitor degradation that is not visible on a basic inspection but is clearly diagnosable with the right equipment.
At Inverter Drive Repair Ltd, we see the summer failure pattern every year. If your drive has been behaving differently in warm weather, or if you want to get an ageing drive serviced before the temperature rises, get in touch.
📞 020 8150 1060 | 📧 info@inverterdriverepair.com