Mitsubishi Electric · FR-D700 Inverter
This fault indicates that the brake transistor has detected an alarm condition, typically due to excessive regenerative energy from the motor. This usually happens during rapid deceleration or when driving high-inertia loads, leading to overheating of the braking components. Continuous overheating can damage the inverter's internal brake circuit and external brake resistor.
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Using an ohmmeter, measure the resistance of the external brake resistor connected between terminals P/+ and N/- (or P/+ and P/DB for internal brake resistors), comparing to the rated value.
Increase the deceleration time (Pr. 8) to reduce the rate of energy regeneration, ensuring it's not excessively short for the load inertia.
Verify the brake resistor parameter Pr. 30 (Brake resistor selection) matches the actual installed resistor type and size.
Check the duty cycle and peak power rating of the external brake resistor to ensure it can handle the application's regenerative energy.
If the brake resistor and deceleration settings are confirmed correct, inspect the inverter for signs of internal brake transistor damage or overheating.