Pros and Cons of Soft Starter

When you are starting a motor, it is always required to start or stop it smoothly based on the load connected or current drawn. This is required for the safety purpose of the motor. This is why motor starters play a very important role in electrical panels.

Contents

A motor cannot function without a starter. There are many types of starters used in electrical systems. In this post, we will see about a soft starter. We will see the various pros and cons of a soft starter in this post.

A soft starter is an electronic device used to control the acceleration of an electric motor. It gradually increases the motor’s voltage, providing a smooth start, reducing mechanical stress, and increasing the motor and machinery’s lifespan.

Soft Starter

As the name implies, a soft starter is the one that starts the motor smoothly. Basically, if the motor is run initially at full load current in its rated speed, then it will heat up the motor windings over a period of time, and also create tensions on the electrical input supply.

For this reason, a soft starter is used which will ramp up the motor in a predefined time. Suppose, a motor is required to run at 40 Hz. Then, the soft starter will reach 40 Hz in suppose 5 seconds.

In these 5 seconds, the motor will ramp up from 0 to 40 Hz, and not directly at 40 Hz. This means that if you set this ramp time properly according to ratings, then your motor will start smoothly every time and run for a longer life.

The motor accelerates smoothly, as the voltage to increases smoothly. This protects the motor against mechanical wear and tear and reduces damage to the bearings.

Soft starter has various programming parameters in it and the most important one is to set the correct acceleration time. This ramps the motor gradually towards the required speed.

Pros of Soft Starter

The very first advantage is it offers a very smooth start to the motor. This avoids large-scale fluctuations in power. Because the voltage increases gradually, the line current too increases gradually and you do not have to worry about the line power consumption.

As the ramp-up time is programmable; you have the flexibility to adjust the motor performance as per your requirement. If this is kept stable for a long time, then the motor life increases.

Motor temperature is kept under control due to a soft start. This prevents overheating and prevents your motor winding or bearing from any future damage.

Frequent starts and stops of a motor can be done smoothly in this starter type. The motor performance is not affected due to this.

Due to the smooth increase of current, torque control is very good in a soft starter. If torque control is good, you get a very good load performance for the motor.

Cons of Soft Starter

When compared to VFD, the first and foremost major disadvantage is the lack of speed control. Soft starter is not able to vary the speed of the motor. This is the reason why despite programming capabilities in softstarters, VFD is the only device used for speed control.

For heavy loads, it is not recommended to use a soft starter. This is because the torque capability of this starter is much lower than VFD, and it will not be able to handle such types of loads.

Types of Soft Starters

Voltage Ramp Soft Starter
Current Limit Soft Starter
Torque Control Soft Starter
Closed-Loop Soft Starter
Digital or Intelligent Soft Starter
Solid-State Soft Starter
Inline Soft Starter
Bypass Soft Starter

Comparison of Soft Starters

Type of Soft Starter	Key Feature	Operation	Application
Voltage Ramp Soft Starter	Gradually increases voltage	Smoothly ramps up the voltage to the motor	Suitable for applications with less stringent torque requirements
Current Limit Soft Starter	Limits start-up current	Controls the current during start to a set level	Ideal for systems where current spikes need to be minimized
Torque Control Soft Starter	Controls starting torque	Provides precise control over the torque applied	Used in applications requiring control over mechanical stress
Closed-Loop Soft Starter	Feedback control mechanism	Adjusts voltage based on feedback from the motor	For applications requiring precise control of start and stop
Digital or Intelligent Soft Starter	Advanced programming and control	Offers detailed control settings and monitoring	High-end applications with specific start/stop requirements
Solid-State Soft Starter	Uses solid-state devices	Provides smooth voltage ramp-up without mechanical contacts	General applications, offering reliability and durability
Inline Soft Starter	Directly installed in line with the motor	Controls the motor by being in the direct power line	Simple installations where space or wiring is a concern
Bypass Soft Starter	Includes a bypass contactor	After start-up, it bypasses itself to reduce heat and save energy	Applications where the soft starter is only needed for start-up