Is your VFD tripping on IGBT Overtemperature? Learn the difference between heat sink and junction temps, and how to fix airflow, switching, and loading issues.

 

Hot Under the Hood: Troubleshooting IGBT Overtemperature

In the heart of every Variable Frequency Drive (VFD) are the IGBTs (Insulated-Gate Bipolar Transistors). These components do the heavy lifting, switching high currents at high speeds to control your motor. However, this work generates significant heat.

When your drive displays a fault like OH, OH1, or F0004, it’s telling you that its internal silicon is approaching its "melting point." Ignoring an IGBT overtemperature fault is the fastest way to turn an expensive VFD into a paperweight.

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Heat Sink vs. Junction Temperature

Most VFDs monitor temperature in two ways:

1. The Heat Sink (NTC/PTC): A sensor mounted on the aluminum cooling block. This is "slow" heat.

2. The Junction (I²t calculation): The drive’s software calculates how hot the actual silicon inside the IGBT is getting based on current draw. This is "fast" heat.

If your drive trips immediately upon starting, it’s likely a Junction issue (high current). If it trips after 20 minutes of running, it’s likely a Heat Sink issue (cooling failure).

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The Common Culprits

1. The "Suffocating" Heat Sink

Over time, industrial dust, oil mist, and lint coat the cooling fins of the VFD. This creates an insulating blanket that prevents heat from escaping.

• The Fix: Use dry compressed air to blow out the cooling fins from bottom to top.

2. Cooling Fan Failure

VFD fans have a finite lifespan (usually 3–5 years in harsh environments). If the fan bearings seize or the fan slows down, the heat sink temperature will skyrocket.

• The Fix: Check if the fan is spinning freely. Many drives have a parameter that shows "Fan Run Time"—if it’s over 40,000 hours, replace it.

3. High Switching (Carrier) Frequency

The faster the IGBTs switch (e.g., 16kHz vs. 4kHz), the quieter the motor, but the hotter the IGBTs get. Switching generates heat every time the transistor flips "on" or "off."

• The Fix: Lower the carrier frequency (e.g., from 8kHz to 4kHz). You might hear more "motor whine," but the drive will run significantly cooler.

4. Excessive Ambient Temperature

If your control cabinet is sitting in a 110°F (43°C) room and has no ventilation, the VFD cannot "reject" its heat into the air.

• The Fix: Improve cabinet ventilation, install a cabinet fan, or add a vortex cooler/AC unit to the enclosure.

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Troubleshooting Checklist

Step	Action	Result
1	Feel the air coming out of the VFD.	If it's weak or cold while the drive is hot, the fan is dead or the fins are clogged.
2	Check Parameter for "Heatsink Temp".	Compare this to the ambient temperature. Anything above 80°C (176°F) is the danger zone.
3	Check Motor Current.	Is the motor pulling more than its rated current? Excess current = Excess heat.
4	Inspect Cabinet Filters.	Dirty intake filters on a cabinet door are the #1 cause of "mystery" overheating.

IGBT Overtemperature is a protective "suicide switch." The drive is shutting down because it can no longer keep itself cool. By maintaining a clean environment and ensuring your fans are functional, you can prevent the thermal runaway that leads to total drive failure