Overbraking

What does ObF mean?

This fault indicates a DC bus overvoltage condition, most commonly caused by the motor regenerating energy back to the drive, such as during rapid deceleration or when driving an inertial load. If the regenerated energy cannot be dissipated, it can cause the DC bus voltage to rise above safe limits. Persistent overvoltage can stress and damage the drive's power stage components (e.g., IGBTs).

• Rapid deceleration of a high-inertia load generating excessive regenerative energy.
• Insufficient or incorrectly sized dynamic braking resistor (R_BR) connected to terminals (e.g., BR+, BR-).
• Braking chopper circuit (internal or external) is not enabled or incorrectly configured (P4-01, P4-02).
• Braking resistor wiring is open circuit or has high resistance.
• DC bus voltage rises above the overvoltage trip threshold (e.g., 810VDC for a 400V drive).

Click steps to track your progress.

1. 1

   1. Increase the deceleration ramp time parameter (P1-12) to allow for slower motor deceleration.

2. 2

   2. Measure the resistance of the dynamic braking resistor (R_BR) directly at the drive's BR+ and BR- terminals.

3. 3

   3. Verify that the braking chopper enable parameter (P4-01) is set to 'Enabled' and the braking level (P4-02) is appropriate.

4. 4

   4. Confirm the braking resistor's power rating and resistance value are suitable for the application's regenerative energy.

5. 5

   5. Check connections between the drive's braking terminals and the braking resistor for integrity and continuity.