Cause : Overvoltage limit comes when the voltage level at the drive's input terminals is exceeding the acceptable operating range.

The alarm A0502 in Siemens Micromaster 420 (MM420) indicates overvoltage limit alarm. This means the drive has detected a voltage in the DC link that exceeds the permissible limit. Here’s how to diagnose and address this issue:

1. Check Supply Voltage:

   • Verify that the input supply voltage to the drive is within the specified range. High supply voltage can cause the DC link voltage to exceed limits.

2. Inspect Deceleration Time:

   • If the drive is decelerating too quickly, the regenerative energy from the motor can cause a temporary increase in DC link voltage.
   • Increase the deceleration time parameter to allow for a slower deceleration, reducing the likelihood of an overvoltage condition.

3. Brake Chopper and Resistor:

   • Ensure that the drive has a functioning brake chopper and braking resistor (if applicable). These components are crucial for dissipating excess energy and preventing overvoltage.
   • Check the brake resistor for proper sizing and correct operation.

4. Check for External Factors:

   • Ensure that there are no sudden changes in load or power supply conditions that could cause voltage spikes.

5. Review Drive Settings:

   • Verify that the drive parameters related to voltage limits are correctly set. Key parameters to check include:
     • DC link voltage limit
     • Brake chopper activation threshold