An electronic device that gradually increases voltage to a motor at start-up to reduce mechanical shock and inrush current.
Full Definition
A soft starter is a reduced-voltage starting device placed between the power supply and an AC motor. It ramps up motor voltage over a programmable time period, reducing the mechanical shock to the motor, gearbox, and sheave at start-up, and limiting the current inrush that can cause voltage drops on the building supply. In elevators, soft starters are used mainly on hydraulic pump motors and on older traction machines that are not fitted with a full VFD. They are simpler and cheaper than VFDs but provide no variable-speed control during the run. After reaching full speed, the motor is often transferred to a bypass contactor to eliminate the soft starter losses. Soft starters also provide overload and phase-loss protection.
