Overbraking

What does ObF mean?

Indicates an overbraking condition. This occurs when the motor is regenerating too much energy back into the drive, exceeding the drive's ability to dissipate it, often due to rapid deceleration or an overhauling load. This can cause the DC bus voltage to rise excessively, potentially damaging the drive.

• Deceleration time (Parameter P2-02) set too short for the motor and load inertia, causing rapid braking and regenerative energy.
• Overhauling load (e.g., crane, fan stopping) feeding kinetic energy back to the drive's DC bus, exceeding dissipation capacity.
• Braking resistor (if installed) is incorrectly sized (too high resistance), disconnected, or failed open circuit.
• Braking transistor (chopper) internal to the drive has failed to activate or switch correctly, preventing energy dissipation.
• Excessive mains supply voltage (overvoltage) contributing to a higher baseline DC bus voltage, reducing overbraking margin.

Click steps to track your progress.

1. 1

   Increase the deceleration time (e.g., Parameter P2-02) by 10-20% and observe if the fault clears during deceleration.

2. 2

   Verify the braking resistor (if installed) is connected to the specified terminals (e.g., R+, R-) and measure its resistance value; compare to nameplate.

3. 3

   Check if the braking resistor is overloaded or overheated; allow it to cool down and inspect for damage to resistor elements or fan.

4. 4

   If no braking resistor is used, consider installing one with appropriate resistance and power ratings for the application's regenerative energy.

5. 5

   Monitor the DC bus voltage (e.g., via Parameter d0-01) during deceleration to confirm it exceeds the overvoltage trip threshold (e.g., 780VDC for 400V drives).