Brake resistor
ABB · ACS880
What does 7181 mean?
The drive detects an issue with the brake resistor, indicating it might be disconnected, physically damaged, or improperly sized. This prevents proper dissipation of regenerative energy, potentially leading to DC bus overvoltage and drive trips during deceleration.
Common Causes
- Brake resistor (BR) disconnected from the drive's BR+ and BR- terminals.
- Open circuit detected in the brake resistor element due to internal damage or wire breakage.
- Incorrect brake resistor value (resistance or power rating) specified in drive parameter P4-01 or P4-02.
- Loose or corroded connections at the brake resistor terminals.
- Faulty internal brake chopper circuit not accurately sensing the resistor.
Repair Steps & Checklist
Click steps to track your progress.
- 1
Power off and lock out the drive. Verify physical connection of the brake resistor to the drive's BR+ and BR- terminals.
- 2
Measure the resistance of the brake resistor across its terminals using a multimeter; compare to the nameplate value.
- 3
Confirm drive parameter P4-01 (Brake Resistor Resistance) matches the measured resistance value within tolerance.
- 4
Inspect brake resistor wiring for breaks, damage, or loose connections.
- 5
Check the drive's fault log for preceding or related brake chopper faults (e.g., 7191 BC short circuit).