RB
Regenerative brake pre-alarm
Mitsubishi Electric · Mitsubishi FR-E800 Variable Frequency Drive
What does RB mean?
This pre-alarm appears if the regenerative brake duty reaches or exceeds 85% of the value set in Pr.70 (Special regenerative brake duty). It's a warning that the regenerative braking capacity is nearing its limit, and a regenerative overvoltage (E.OV[]) fault may occur if it reaches 100%.
Common Causes
- Regenerative braking energy exceeding capacity during deceleration.
- Regenerative brake resistor approaching thermal limit.
- High DC bus voltage detected during regenerative braking event.
Repair Steps & Checklist
Click steps to track your progress.
- 1
Set the deceleration time longer to reduce the instantaneous regenerative energy and duty.
- 2
Check the brake resistor duty to ensure it is not too high for the application, possibly requiring a larger resistor.
- 3
Verify the settings of Pr.30 (Regenerative function selection) and Pr.70 (Special regenerative brake duty).
Verified technical data. Last updated: March 2026
Related Faults
Source: Mitsubishi FR-E800 Variable Frequency Drive