Applicable Systems
EFC
FEX
FEI
HNC
Symptoms
Maximum braking time exceeded. The drive has detected that the braking (deceleration) time has exceeded the configured maximum, indicating the brake system is not performing as expected.
Possible Causes
- Brake resistor power rating insufficient for the regenerative energy
- Brake chopper not activating properly
- Mechanical brake worn or not engaging
- Deceleration parameter set too short for the load inertia
Troubleshooting Steps
- Step 1: Check brake resistor resistance and power rating against calculated values
Resistor matches or exceeds calculated requirements - Step 2: Verify brake chopper activation in the drive diagnostic
Chopper activates during deceleration; DC bus voltage stays below trip threshold - Step 3: Test mechanical brake engagement and holding torque
Brake engages within rated time and provides full holding torque - Step 4: Adjust deceleration time if the load inertia requires longer braking
Updated deceleration time is achievable with available braking capacity
How to Reset
1) Check brake resistor. 2) Verify chopper operation. 3) Test mechanical brake. 4) Adjust deceleration time. 5) Reset fault.
Frequently Asked Questions
- Q: How do I calculate required brake resistor power?
P = (J * omega^2) / (2 * t_decel) where J is total inertia, omega is angular velocity, and t_decel is deceleration time. Add safety margin of 20%.
- Q: What happens if braking time keeps exceeding the limit?
The drive will eventually trip on DC bus overvoltage. The brake system must be properly sized to absorb regenerative energy during deceleration.
Source: Rexroth IndraDrive HCS/HMS Fault Code List, Bosch Rexroth AG
Category: PLC & VFD