Emerson O.ht1: Emerson Unidrive SP Error Code O.ht1

Symptoms

The drive trips and displays O.ht1, indicating power module overheat. The thermal sensor on the power module heatsink has detected that the temperature has exceeded the trip threshold, causing the drive to shut down to protect the IGBT modules.

Possible Causes

Ambient temperature inside the enclosure exceeds the rated 40-50C
Cooling fan stopped or running at reduced speed due to failure
Heatsink fins blocked by dust or debris
Drive operating at sustained high current near its rated limit

Troubleshooting Steps

Step 1: Check the ambient temperature inside the electrical enclosure
Temperature should be below 45C; if above, improve ventilation or install cooling
Step 2: Verify the cooling fan is running at full speed
Fan should spin freely without noise; replace if seized or noisy
Step 3: Clean the heatsink fins using compressed air
Fins should be clear of dust; verify airflow passage with a light test
Step 4: Measure the drive output current during operation
If current is consistently above 90% of rated, consider a larger drive or reduce the load

How to Reset

To reset: 1) Allow the drive to cool for at least 10 minutes. 2) Fix the cooling issue. 3) Press RESET. 4) Restart. Caution: Do not immediately reset without allowing the heatsink to cool; the IGBT junction temperature may still be high.

Common Replacement Parts

CT-FAN-SP5: Unidrive SP cooling fan assembly (Match to drive frame size; verify airflow direction before installation)

Frequently Asked Questions

Q: What temperature triggers O.ht1?
The power module overheat trip occurs at approximately 90-100C on the heatsink (varies by model). A warning is issued at a lower threshold, giving time to act before a trip.
Q: How often should I clean the heatsink?
Inspect every 6 months in a typical factory environment, or monthly in dusty environments. Clogged heatsinks are the leading cause of overheat trips and premature IGBT failure.

Emerson Unidrive SP Error Code O.ht1