Soft starters are designed to limit current or soft start (ramp up the voltage) of a motor.
The same holds true for braking or soft stopping. Simple settings perform the start and stop well.
So what about in-between the start and the stop? Do you continue to use silicon-controlled rectifier (SCR) control or do you utilize a bypass contactor?
Some soft starters are fully solid-state - meaning no bypass is needed - and are IEC rated AC-53a for running on SCR control continuously on a squirrel-cage motor. Other soft starters are hybrids, which means that they are rated AC-53b intermittent duty and use a bypass when the motor is up to speed.
Fully solid-state soft starter advantages:
The hybrid soft starters typically contain SCRs not rated for continuous duty because this controller is designed to utilize SCRs to start and stop, and no more. Use of a bypass contactor, either internal or external, allows an application to run continuously after the starting algorithm stops and the motor is at-speed. The bypass will open once a stop or fault command has been provided.
Advantages of an internal bypass:
Advantages of an external bypass:
Best applications for hybrid soft starters:
Know the motor application that will be controlled by the soft starter. After the start and stop method is selected, think about how the run mode in between is to operate. Then pick the appropriate run mode to fit the application. To assist with the thought process, ask the following about the application:
For further information on bypass control Soft Starter Bypass Technology in Smart Motor Controllers.