7181 Brake Resistor Fault in ABB ACS880 Drive

7181 Brake Resistor in the ABB ACS880 Drive indicates that the drive has detected a problem with the dynamic brake resistor circuit. The ACS880 continuously monitors the brake chopper and brake resistor to ensure that excess regenerative energy can be safely dissipated during motor deceleration or overhauling loads. If the drive detects that the brake resistor is broken, disconnected, or not functioning correctly, it generates Fault 7181 to protect the drive from excessive DC bus voltage and potential hardware damage.

This fault generally indicates a problem with the brake resistor, brake resistor wiring, brake chopper circuit, or resistor sizing, rather than a fault in the motor itself.

Possible Causes

  • Brake resistor is not connected.
  • Brake resistor is open circuit or broken.
  • Loose or damaged brake resistor wiring.
  • Poor connection at the brake resistor terminals.
  • Incorrectly sized brake resistor.
  • Brake resistor resistance value outside ABB specifications.
  • Defective brake chopper circuit.
  • Faulty brake chopper transistor.
  • Damaged brake resistor terminals.
  • Internal wiring fault between the brake chopper and resistor.
  • Brake resistor overheated and failed.
  • Incorrect installation after maintenance.
  • Internal power unit hardware failure.
  • Electrical surge damaging the brake resistor circuit.
  • Moisture or contamination affecting the brake resistor connections.
  • Defective control or monitoring circuit.

Solutions

  • Cycle power to the drive and check whether the fault clears.
  • Verify that a brake resistor is installed if required by the application.
  • Inspect the brake resistor for physical damage or overheating.
  • Measure the brake resistor resistance and compare it with ABB specifications.
  • Verify that the brake resistor is correctly sized for the drive and application.
  • Inspect all brake resistor wiring for loose or damaged connections.
  • Check the brake resistor terminals for corrosion or poor electrical contact.
  • Inspect the brake chopper circuit for hardware faults.
  • Verify the brake chopper operates correctly during braking.
  • Inspect the internal wiring between the brake chopper and resistor.
  • Replace the brake resistor if it is open circuit or damaged.
  • Replace damaged wiring or connectors.
  • Replace the brake chopper if defective.
  • Replace the power unit if internal hardware failure is confirmed.
  • Contact ABB technical support if the fault persists after hardware inspection.

Additional Information

The ABB ACS880 uses a dynamic braking system to safely dissipate regenerative energy generated by the motor during rapid deceleration or when driving overhauling loads. This energy is transferred to the brake resistor through the brake chopper, preventing the DC bus voltage from rising to unsafe levels.

The drive continuously monitors the brake resistor circuit. If the resistor is missing, disconnected, open circuit, or incorrectly sized, the drive cannot safely dissipate regenerative energy and generates Fault 7181.

Unlike a DC bus overvoltage fault, Fault 7181 specifically indicates that the brake resistor circuit itself is faulty or unavailable, rather than the DC bus voltage already exceeding its protection limit.

Applications with frequent stopping, rapid deceleration, elevators, cranes, centrifuges, or high-inertia loads are especially dependent on a properly functioning brake resistor.

Common Symptoms

  • Drive trips with Fault 7181.
  • Drive will not perform rapid deceleration.
  • Fault appears during braking or stopping.
  • DC bus voltage increases during deceleration.
  • Frequent faults during high-inertia stopping.
  • Brake resistor remains cold because it is disconnected.
  • Brake resistor shows visible signs of overheating or damage.
  • Fault remains after reset.
  • Fault may occur immediately after brake resistor replacement.
  • Drive limits braking performance.

Recommended Troubleshooting Sequence

  1. Cycle power to the drive.
  2. Verify that a brake resistor is installed if required.
  3. Inspect the brake resistor for physical damage.
  4. Measure the brake resistor resistance.
  5. Confirm the resistor is correctly sized for the drive.
  6. Inspect the brake resistor wiring.
  7. Verify all resistor terminals are securely connected.
  8. Inspect the brake chopper circuit.
  9. Check the brake chopper operation during braking.
  10. Inspect internal wiring between the brake chopper and resistor.
  11. Replace the brake resistor if defective.
  12. Replace damaged wiring or connectors.
  13. Replace the brake chopper or power unit if hardware failure is confirmed.
  14. Contact ABB technical support if the fault persists.

Brake Resistor Check Table

Check PointAction
Power cycleRestart the drive
Brake resistorVerify it is installed and properly connected
Resistor conditionInspect for overheating or physical damage
Resistance valueMeasure and compare with ABB specifications
Resistor sizingConfirm correct rating for the application
Brake resistor wiringInspect for loose or damaged connections
Resistor terminalsEnsure secure electrical connections
Brake chopperVerify proper operation
Internal wiringInspect between brake chopper and resistor
Power unitInspect for hardware faults
PCB conditionCheck for contamination or burn marks
ABB technical supportContact if the fault remains after inspection

Preventive Maintenance Tips

  • Inspect the brake resistor during scheduled maintenance.
  • Periodically measure the brake resistor resistance to detect deterioration.
  • Ensure the brake resistor is correctly sized for the application and duty cycle.
  • Tighten brake resistor terminals according to ABB torque specifications.
  • Keep the resistor and surrounding area free from dust and debris to promote cooling.
  • Verify adequate ventilation around the brake resistor to prevent overheating.
  • Inspect brake chopper wiring for signs of wear or insulation damage.
  • Protect the drive and braking circuit from electrical surges.
  • Use only ABB-approved brake resistors or resistors meeting ABB specifications.
  • Record recurring brake resistor faults to assist long-term diagnostics.

Proper inspection of the brake resistor, verification of resistor sizing, secure wiring connections, routine maintenance of the brake chopper circuit, and timely replacement of damaged braking components will help prevent recurring 7181 Brake Resistor faults in ABB ACS880 drives, ensuring safe dissipation of regenerative energy, reliable braking performance, and long-term protection of the drive's power electronics.

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