Drive Fault Code 7902 — Siemens

Inspect the encoder cables for shielding defects, loose connections, or proximity to high-voltage power cables (EMI noise can corrupt encoder signals).

Jams in conveyors, pumps, mixers, or gearboxes physically lock the rotor.

Diagnosis requires looking at the hardware, the application, and the software parameters:

Rotate the driven equipment manually to check for binding, jams, or broken gearboxes. Step 2: Electrical and Wiring Inspection siemens drive fault code 7902

In hoisting or vertical axis applications, a mechanical holding brake is often used. If the brake fails to release (due to a blown rectifier or sticky mechanism), the drive attempts to move against a locked brake, resulting in an immediate 7902 fault.

The motor is drawing maximum allowable current ( p0640p 0640

When fault 7902 appears:

| Parameter | Description | Typical Value | |-----------|-------------|----------------| | p2040 | Monitoring time for telegrams (ms) | 100–500 ms | | p0922 | Telegram configuration (e.g., 1, 352, 999) | Match PLC configuration | | r2060 | Telegram received? | Should increment cyclically | | p8700 (PROFIBUS) / p8839 (PROFINET) | Station address / device name | Unique and matching PLC |

While this fault is common across various series including , its root causes can range from simple mechanical blockages to complex parameterization errors. Primary Causes of Fault 7902

) forces the drive to hit its current limit immediately. If it cannot accelerate the load to the target speed before the stall timer expires, F07902 trips. 5. Sensorless Vector Control Issues at Low Speeds Inspect the encoder cables for shielding defects, loose

The threshold speed for stall detection (p2175) or the stall delay time (p2177) may be configured too aggressively for the specific application. 3. Motor and Control Mode Mismatches

Attempting to accelerate a heavy, high-inertia load too quickly via an aggressively short ramp-up time ( p1120p 1120

Applications with periodic load spikes (crushers, punch presses, conveyors with sticky product). Go to parameter P2178 . The default is often 0.010 . Increase it: Step 2: Electrical and Wiring Inspection In hoisting

The actual motor speed has exceeded the p2162 (overspeed threshold) value for longer than the time set in p2163 .