Soft Starters

FAQs

Do motor soft starters provide motor speed control and torque control for ac motors and dc motors?

Motor soft starters are primarily designed to provide motor speed control and torque control for AC induction motors. However, some soft starters may also be capable of providing control for certain types of DC motors.

What is the difference between electrical soft starters and mechanical soft starters?

The main difference between the two soft starters is the way in which they control the starting current and torque of an electric motor. Electrical soft starters use electronic components, such as thyristors or power transistors, to control the voltage supplied to the motor during the starting process. Mechanical soft starters use mechanical components, such as autotransformers or reactors, to gradually increase the voltage supplied to the motor.

How are soft starters connected to the motor in relation to the power supply?

Soft starters are typically connected in series with the motor between the power supply and the motor itself.

Do most soft starter models protect motors from a power surge?

Most soft starter are designed to protect motors from a range of electrical issues, including power surges. Other protections include overload protection, under-voltage protection, over-voltage protection, voltage drop and short circuit protection.

What is the motor voltage of an induction motor?

Common voltage ratings for induction motors include 208 volts, 230 volts, 460 volts, and 575 volts, among others. The specific voltage rating of a motor will depend on a variety of factors, including the size, power rating, and intended application of the motor.

Motor Starters, Soft Starters and VFDs

Motor Starters

Motor starters safely start and stop a motor in industrial applications. They are designed with a contactor, overload and circuit protection. They are used when basic motor control is required, where torque on the motor is not a concern and speed control is not needed. The advantages of motor starters include: lower cost, allows for remote operation, allows for monitoring of motor state (with the use of auxiliary contacts) and they are safe and efficient. The disadvantages include: high inrush current that can cause fuses to blow and breakers to trip if the inrush is too high, and the starter will allow a full torque to start the motor which can cause the motor to ramp up to full speed very quickly potentially causing the motor to wear and degrade prematurely.

Soft Starters

Soft starters protect motors from inrush current by gently ramping up the motor to full speed. They provide all of the same functions as a traditional motor starter. The advantages of soft starters include: they are less expensive than a VFD when only startup control is needed, they are a smaller system than a VFD where space is a concern and they prevent unwanted torque upon startup, prolonging the life of the motor. The disadvantages include: they are more expensive than a traditional motor starter and they do not allow for full speed control. 

VFDs

Variable Frequency Drives (VFDs) allow for the slow ramp up of a motor during startup and the slowing down of the motor during shutdown. They also allow for full speed control during the entire run cycle of the motor. VFDs provide the same functions as both the traditional motor starters and soft starters. The advantages of VFDs include: full speed control (start, stop and in-between), more custom control and monitoring, energy savings due to efficient motor usage and less wear and tear on the motors. The disadvantages include: they are more expensive and larger than other motor control options and they generate heat that may require fans or AC units.