How Does Soft Start Work?

By definition, a soft starter can refer to any device which can control the acceleration of a motor by controlling the voltage that is applied. This includes industry soft starters for motors and induction motors. An induction motor has this self starting ability because of the interaction that occurs between the rotating magnetic field flux and the rotor winding flux. This interaction causes a high rotor current as the torque is increased. By the time the motor reaches its maximum speed, the large current force can cause overheating of the motor which as we know can damage motors. If you work with motors that seem to be pushing past their limits and burning out too quickly you should consider investing in industry soft starters for motors.

Soft Starter

The duty of a soft starter is to reduce the torque that is applied to the electric motor. It is made up of devices known as thyristors which control the main supply of voltage to the motor. The torque can be adjusted by reducing the voltage at the same time the motor has been started this is because they are all proportional to each other. There are two main types of control that you can get by using a soft starter:

The first type of control is open control. Without the current drawn or the speed of the motor, the start voltage is applied. In this control, there are two SCR’s connected back to back to each other and are conducted 180 degrees in half wave cycles. The delay of 180 degrees is gradually reduced until the applied voltage goes up to the full supply voltage capacity. This process is also known as the time voltage ramp system, this method does not control the motor acceleration. The second type of control is closed loop control. In this process, all the motor output characteristics are monitored including the current drawn and the speed. The starting voltage is also modified accordingly to get the required response. The current in each element is monitored and if one of the elements exceeds its limits the whole time voltage ramp is stopped.

Now that we have a basic concept of how industry soft starters for motors work we can go over some of the advantages:


  • Improved efficiency is one of the advantages of the solid state switches that you find in a soft starter system are lower on state voltage.
  • Controlled start up is another advantage which means you can easily start the motor without any jerks or halts, this is because the start current is controlled meaning it is released smoothly.
  • Controlled acceleration is another advantage and gives you motor acceleration that is controlled in a smooth manner. It is also cheaper and smaller than some other methods.


They are an effective way to drop costs, repairs, and to save time and money. They will boost efficiency and bring you a whole range of advantages that you didn’t know you needed until now. Boosting the life of your motors can mean a lot of money, stress, and time saved. Nearly every industry runs with some kind of motor, protect your motor now with industry soft starters for motors.