Solid-state motor starters combine solid-state circuitry to provide the function of a traditional motor starter. Fig. 1 shows several solid-state motor starters. From this figure notice that the motor starter has six potentiometers mounted on the face of the starter. These potentiometers provide a means to set the ramp-up and ramp-down functions for the motor. This feature is called soft starting. The traditional motor starter is called an across-the-line starter, which means that the main contacts close and provide full voltage to the starter the instant the coil is energized. The solid-state starter provides voltage that increases slowly (ramps) to allow the motor to start turning its shaft slowly and increasing to full rpm. The solid-state motor starter also provides adjustable overloads. Additional potentiometers on the face of the starter allow one to adjust the percentage of overload from 0-400% and the amount of time the overload current is allowed to occur.
The solid-state motor starter uses triacs and transistors for power control in AC motor starters, and SCRs and transistors for DC motor starters. These controls have provided the function of a traditional motor starter, yet provide additional protection for the motor. This is possible by using solid-state devices on the inexpensive models, and by using microprocessors on the more expensive models.
Above: Fig. 1: Solid-state motor starters. The lower unit also provides
soft-starting functions for motors.
