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. 1

    Set the deceleration time longer to reduce the instantaneous regenerative energy and duty.

  2. 2

    Check the brake resistor duty to ensure it is not too high for the application, possibly requiring a larger resistor.

  3. 3

    Verify the settings of Pr.30 (Regenerative function selection) and Pr.70 (Special regenerative brake duty).

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Verified technical data. Last updated: March 2026

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Source: Mitsubishi FR-E800 Variable Frequency Drive