Brake resistor

What does A791 mean?

The brake resistor is either broken or not connected. This means the drive cannot dissipate regenerative energy, which can lead to overvoltage faults when decelerating or braking. The drive's ability to stop or manage energy is compromised.

• Brake resistor wiring is open-circuited, loose, or disconnected from the drive's `R+, R-` terminals.
• Internal element of the brake resistor has failed (e.g., resistive wire broken due to overheating or mechanical stress).
• Incorrect connection, such as connecting the resistor to the wrong terminals or using a resistor with an impedance outside the drive's permissible range.
• Faulty internal brake chopper circuit or measurement in the drive itself.

Click steps to track your progress.

1. 1

   Power down the drive. Disconnect the brake resistor leads from the drive's `R+` and `R-` terminals.

2. 2

   Measure the resistance of the brake resistor directly with an ohmmeter (e.g., `Fluke 179`). Compare the measured value to the nominal resistance specified on the resistor's label (e.g., `20 Ohms`).

3. 3

   Inspect the brake resistor cabling for physical damage, insulation breakdown, and secure connections at both the resistor and drive terminals.

4. 4

   Verify that the resistor's nominal resistance (`P43.08` (Brake resistor resistance)) and power (`P43.09` (Brake resistor power)) parameters are correctly entered in the drive.

5. 5

   Check for visual signs of damage on the resistor, such as burn marks, discoloration, or broken resistive coils.