In the context of Siemens SINAMICS drives (such as the G120 or S120), Fault Code F7902 signals that the motor has stalled
. This critical protection fault occurs when the drive detects that the difference between the set speed and actual speed has exceeded a defined tolerance for too long, often because the motor cannot generate enough torque to overcome the load. Siemens SiePortal 1. Primary Causes of F7902 Mechanical Overload:
The load on the motor is significantly higher than its rated capacity, preventing it from reaching the set speed. Incorrect Motor Data:
The drive lacks accurate motor nameplate parameters (e.g., rated power, current, or power factor), leading to inefficient torque calculation. Incomplete Commissioning: Skipping the Motor Data Identification
(Motor ID) or rotating measurement prevents the drive from modeling the motor’s electrical characteristics. Encoder/Wiring Issues: siemens drive fault code 7902
Faulty speed feedback from an encoder or incorrectly connected motor cables (e.g., swapping U and W phases) can cause the drive to "think" the motor is stalling. Brake Malfunction:
If a mechanical brake does not release properly when the motor starts, the motor will stall against the brake. 2. Standard Troubleshooting Steps
To resolve F7902, users typically follow a structured diagnostic process: Validate Motor Parameters: Ensure parameters such as (rated voltage), (rated current), and (rated speed) exactly match the motor's physical nameplate. Perform Motor ID: Re-run the identification procedure using
(identification at standstill). This helps the drive calculate the correct control parameters. Check Mechanical Integrity: In the context of Siemens SINAMICS drives (such
Decouple the motor from the load to see if the fault persists. If it runs fine while decoupled, the issue is likely the mechanical load or an unreleased brake. Enable Flying Restart:
If the fault occurs when trying to start a motor that is already spinning (coasting), enable the "Flying Restart" function ( Adjust Fault Limits:
If the stall is temporary and expected for the application, you can increase the (delay time) or the (fault tolerance) to prevent nuisance tripping. Siemens SiePortal 3. Comparison with Related Fault Codes Key Difference Motor Blocked
Detected at very low speeds/standstill when the speed controller is at its limit. Motor Overspeed Q1: Can I bypass fault 7902 temporarily
The motor is spinning faster than the allowed maximum limit. Motor Stalled
The motor is running but cannot match the speed setpoint due to load or tuning. For detailed technical guides, engineers often refer to the Siemens Industry Online Support (SIOS) for a particular drive model like the sinamics drive motor fault 7902 - SiePortal - Siemens
Yes, by setting p0600 = 0 (disable temperature monitoring). However, this removes overtemperature protection – emergency use only.
To fix the problem permanently, you must identify why the phase failure occurred. Causes fall into four main categories:
Access fault buffer: r0947 lists last 8 faults. r0949 gives additional info (e.g., temperature at time of trip). This helps separate actual overheat from sensor failure.