Siemens SINAMICS G120 fault F07900: Motor blocked
Fault F07900 on a SINAMICS G120 means the motor operated at the torque limit for longer than p2177 while below the speed threshold p2175, so the converter declared it blocked. Siemens notes it can also be triggered by an oscillating speed loop or by the power unit’s thermal monitoring reducing the current limit.
Diagnose this with AI
Try Free Drive Diagnostic Upload a keypad photo, the fault history or a parameter export from your Siemens SINAMICS G120. InduQT compares the evidence and suggests the next useful checks.
When it happens
- At start against a jammed or braked load
- At low speed under heavy load
- Running, when the current limit is reduced thermally
Likely causes and checks
1Mechanical jam or brake not released
- Points to it
- Motor does not turn or barely turns before the trip.
- Check
- Check that the motor can rotate freely and the holding brake releases.
2Torque limit too low for the load
- Points to it
- Trips at heavy load; r1538/r1539 lower than needed.
- Check
- Check the torque limits r1538 (positive) and r1539 (negative).
3Detection thresholds too tight
- Points to it
- Trips on normal slow, heavy starts.
- Check
- Check p2175 (speed threshold) and p2177 (delay time) for the application.
4Current limit reduced by Power Module thermal monitoring
- Points to it
- Trips after long running in a hot cabinet; A05000 alarms beforehand.
- Check
- Check p0290 (power unit overload response) and cabinet cooling.
5Oscillating speed controller
- Points to it
- Speed hunts before the trip.
- Check
- Review speed controller tuning.
Telling it apart
- F07900 is a time-at-torque-limit detection. F07902 (Motor stalled) is a vector-control stall detection; Siemens’ remedy points to motor data and motor identification.
- F07801 trips on current, not on time at torque limit.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| p2175 | Motor locked speed threshold | Below this speed at torque limit counts as blocked. |
| p2177 | Motor locked delay time | Time at torque limit before the fault. |
| p0290 | Power unit overload response | Can reduce the current limit when the power unit is hot. |
Evidence to collect
- r0945/r0948 for F07900 and preceding alarms
- Torque limits r1538/r1539
- p2175, p2177 settings
- Brake status and whether the shaft turns freely
- Cabinet temperature and A05000 history
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