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ALARM 9

Inverter overload

Danfoss · VLT HVAC Drive High Power

What does ALARM 9 mean?

The frequency converter has been operating with more than 100% overload for too long, triggering a warning at 98% and an alarm at 100%. The unit will trip, and cannot be reset until the internal thermal counter falls below 90%. Prolonged overload can severely damage the inverter's power components.

Common Causes

  • Motor or application load exceeding the frequency converter's continuous current rating (e.g., >100% of P1-05 Motor A).
  • Incorrect frequency converter sizing for the connected motor and application's duty cycle.
  • Motor current parameters (e.g., P1-05 Motor A) incorrectly set, leading to an inaccurate thermal model.
  • High ambient temperature around the frequency converter, reducing its continuous current capacity.
  • Blocked or restricted cooling fan/heatsink on the frequency converter, preventing adequate heat dissipation.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Monitor the output current (parameter 16-10 Output Current) and load percentage (parameter 16-16 Load % on converter) during operation.

  2. 2

    Verify the frequency converter's continuous current rating against the maximum operating current of the application.

  3. 3

    Check ambient temperature around the frequency converter enclosure and ensure it is within the specified operating limits.

  4. 4

    Inspect the frequency converter's cooling fan for obstruction or failure and clean heatsink fins if dusty.

  5. 5

    Review motor data parameters (P1-03 Motor kW, P1-04 Motor V, P1-05 Motor A, P1-06 Motor cos phi) to ensure accurate motor model.

  6. 6

    Reduce the mechanical load on the motor or consider oversizing the frequency converter if overload persists.

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Verified technical data. Last updated: April 2026

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Source: Danfoss VLT HVAC Drive High Power
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