Mitsubishi MR-J4 AL.33 Overvoltage during deceleration, what to check?
I'm getting an AL.33 fault on my Mitsubishi MR-J4 servo amplifier, but only when the motor decelerates. What should I check first to resolve this overvoltage issue?
The AL.33 Overvoltage alarm on a Mitsubishi MR-J4 servo amplifier indicates the DC bus voltage has exceeded its prescribed limit. When this fault occurs specifically during deceleration, it often points to an issue with the regenerative braking system. The motor regenerates energy during deceleration, which can cause the bus voltage to rise if not properly managed.
Likely causes and checks
1Regenerative option set incorrectly
- Points to it
- If the regenerative option (resistor) is not configured correctly, the servo amplifier cannot dissipate the regenerated energy effectively, leading to an overvoltage condition. This is common after initial setup or if the resistor has been changed.
- Check
- Verify the regenerative resistor (regenerative option) is correctly installed and check the [Pr. PA02] parameter setting in the servo amplifier.
2Regenerative option not connected or open circuit
- Points to it
- An improperly connected or open-circuited regenerative resistor prevents the dissipation of regenerated energy, causing the bus voltage to rise. The resistor might be fitted but remain cold, or its resistance could be abnormal.
- Check
- Inspect the connections to the regenerative option and measure the resistance of the built-in resistor or external regenerative option to ensure it's within specifications.
3Regeneration capacity insufficient
- Points to it
- If the regenerative resistor's capacity is too small for the application's deceleration demands, it cannot dissipate enough energy, leading to overvoltage. This is often indicated if lengthening the deceleration time constant resolves the alarm.
- Check
- Try setting a longer deceleration time constant and observe if the alarm stops. If it does, consider fitting a larger regenerative option to increase the system's regeneration capacity.
4Input supply voltage too high
- Points to it
- While less likely if the alarm only occurs during deceleration, an excessively high input supply voltage can contribute to or directly cause an overvoltage condition on the DC bus. This would typically cause the alarm even without motion or during gentle stops.
- Check
- Measure the input voltage to the servo amplifier. For a 200 V class amplifier, the voltage should not exceed 264 V AC, and for a 400 V class, it should not exceed 528 V AC.
Next check: Given the alarm occurs specifically during deceleration, the most likely cause is related to the regenerative braking system. Start by checking the regenerative option's settings and connections, as well as its resistance. Then, evaluate if the regeneration capacity is sufficient for your application.
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