Danfoss FC 302 trips Alarm 9 after running loaded for a while, why?
My Danfoss FC 302 on a conveyor system keeps tripping Alarm 9 (Inverter Overload) after running for about 10-15 minutes under load. It doesn't trip instantly, but builds up over time. What should I check first?
Alarm 9 (Inverter Overload) on a Danfoss FC 302 indicates the drive has operated above 100% overload for an extended period, causing its electronic thermal inverter protection counter to reach 100%. The drive cannot be reset until this counter drops below 90%. This fault typically occurs during sustained high loads or repeated heavy starts, accumulating over minutes rather than tripping instantly.
Likely causes and checks
1Load above the drive’s continuous rating
- Points to it
- The drive is running with an output current exceeding its continuous rated current, causing the inverter's thermal load counter to increase and eventually trip the alarm.
- Check
- Compare the output current shown on the LCP with the drive's rated current. Monitor the thermal drive load reading on the LCP to see if it rises above its continuous rating.
2Mechanical overload in the driven machine
- Points to it
- Increased friction or resistance in the conveyor system's mechanical components (e.g., bearings, gearbox) is causing the motor to draw more current, which in turn overloads the drive.
- Check
- Measure the motor current and compare it with historical data. Inspect the driven machine (conveyor system) for any mechanical issues or changes in process load.
3Drive reading does not match the real motor current
- Points to it
- The current displayed on the drive's LCP might not accurately reflect the actual current being drawn by the motor, leading to an incorrect assessment of the load.
- Check
- Compare the output current shown on the LCP with a reading from a clamp-meter on the motor current. Also, verify motor data parameters 1-20 to 1-25 in the drive.
4Drive undersized for the duty
- Points to it
- The drive may be inadequately sized for the current application, especially if there have been recent changes to the application, a larger motor, or a more heavy-duty cycle is being performed on a drive rated for normal duty.
- Check
- Check the drive type code (parameter 15-45) and compare it against the motor specifications and the actual duty cycle requirements of the application.
Next check: First, compare the output current shown on the LCP with the drive's rated current and monitor the thermal drive load reading. This will help determine if the drive is simply operating above its continuous rating.
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