Problem:

A PCS controller ramps the motor up to speed. At speed, the auxiliary contact closes. The PCS controller then stops the motor and restarts the motor continuously, and appears to pulse the motor. The red light stays on all of the time on the PCS soft starter. There are no faults on the PCS controller. Why does the PCS soft starter continually start and stop the motor?

Cause:

The motor is not sized correctly for the PCS controller.

After the motor comes up to speed, the internal built-in bypass contactor closes and the PCS soft starter begins monitoring the phase current and voltage for faults. If the run-mode motor current is low, then it is difficult for the PCS soft starter to distinguish between low run-mode motor current and disconnected motor leads (motor leads are disconnected after the motor is up to speed). Instead of faulting for an open load, the PCS soft starter will attempt to restart the motor. If the motor is undersized for the PCS soft starter, the motor will continue to attempt re-start.

Solution: This re-start behavior will be exhibited using an undersized motor, i.e. a ¾ HP motor that draws less than 1 amp during running and using this motor with the PCS-009-600V controller. It is recommended that the correctly sized PCS controller be used for the motor FLA. The motor FLA should be within the minimum and maximum range shown on the PCS controller's front cover. In the case of the PCS-009-600V controller, the motor full load current range supported is between 3 and 9 amps.

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