Siemens SINAMICS S120 on Servo Press: F07801 and F07802 Fault Diagnosis

admin

The F07801 and F07802 faults on Siemens SINAMICS S120 drives are motor overcurrent faults that appear frequently in servo press applications during high-load forming cycles.

## F07801: Motor Overcurrent

This fault triggers when the motor current exceeds the maximum current limit (p0323) for longer than the allowed time.

Common causes in press applications:
- Forming force exceeds the motor torque capacity at the programmed speed
- Motion profile approach speed too high causing current spike at die contact
- Ambient temperature above 40C reducing drive continuous current rating
- Blocked motor cooling fan

Diagnosis steps:
1. Check r0068 (actual current value) at the moment of fault using the trace function
2. Compare to p0323 (maximum current limit) - if r0068 is hitting p0323, the motor is undersized or the load is too high
3. Check r0035 (motor temperature) - above 120C indicates thermal overload
4. Check r0037 (power unit temperature) - above 80C indicates drive cooling problem

Fix sequence:
- If current spike at die contact: reduce approach speed in the motion profile, add a creep phase 10mm before contact
- If sustained overcurrent during forming: reduce SPM or forming speed
- If thermal: clean cooling fins, verify fan operation, check ambient temperature

## F07802: Motor Overcurrent (Hardware)

This is a hardware-detected overcurrent, more serious than F07801. The drive hardware protection triggered before the software limit.

Immediate actions:
1. Do NOT reset and continue - investigate first
2. Check for short circuit in motor winding: measure resistance between phases (should be equal, typically 0.5-5 ohm)
3. Check for ground fault: measure resistance from each phase to ground (should be >1 megaohm)
4. Check DC bus voltage (r0070): if below 500V during fault, the supply is dropping out

## SINAMICS S120 Trace Function for Press Diagnostics

The trace function is essential for press fault diagnosis. Configure it to capture:
- r0068 (actual current)
- r0061 (actual speed)
- r2521 (position actual value)
- Trigger on F07801

This gives you the current waveform for the 2 seconds before the fault, showing exactly which part of the stroke caused the overcurrent.

mike_chen_eng

Great writeup on F07801. One thing I'd add from experience: on S120 with PM motors, always check the motor temperature sensor wiring before assuming the motor is actually overheating. I've seen corroded connectors on the motor feedback cable cause false F07801 alarms on three separate Bruderer presses. Cleaned the connector, alarm never came back.

mike_chen_eng

**Related guides:** If you resolved the F07801 alarm, you may also want to check [Servo Press Annual Maintenance Schedule](https://servopress.club/d/83) to prevent recurrence, and [Yaskawa Sigma-7 A.74 Overload Alarm](https://servopress.club/d/98) if you see overload faults after the motor repair.