A soft starter and a variable frequency drive (VFD) are both tools used to manage and control the starting and halting of electric motors, but they act differently and have different purposes. The following are the main variations between a VFD and a soft starter:

1. Function:

  • VFD: By adjusting the frequency and voltage provided to the motor, a VFD, sometimes referred to as an AC drive or inverter, is generally used to control the speed and torque of an AC motor. It is appropriate for applications needing speed control, energy savings, and process optimisation since it enables exact control over motor speed and acceleration.
  • Soft Starter: By gradually raising or lowering the voltage provided to the motor during startup and shutdown, a soft starter controls how quickly an electric motor starts and stops. Its primary purpose is to lessen the first current surge that happens at motor startup, hence reducing the mechanical stress on the motor and connected devices. A soft starter ensures a gentle acceleration of the motor by gradually increasing the voltage, avoiding abrupt torque and current spikes. Soft starts offer a regulated and soft start, decreasing the motor’s wear and tear and extending its life. They are frequently used in equipment like pumps, fans, compressors, and other devices that don’t require continuous speed control, where decreased voltage beginning is adequate.

2. Motor Control

  • VFD: Motor speed and torque can be controlled precisely with a VFD. It allows for customizable speed and acceleration profiles by allowing for changes in the frequency and voltage supplied to the motor. In applications like speed control, position control, and energy optimisation, VFDs provide the capacity to operate motors at various speeds, including below the rated speed.
  • Soft Starter: With a steady increase in voltage and a reduction in starting current, a soft starter regulates the voltage applied to the motor during startup. The soft starter, however, no longer affects motor speed control once the motor has reached full speed. Unlike VFDs, soft starts do not offer constant speed control.

Check: Rockwell Automation 22F-D6P0N103 PowerFlex 4M AC Drive

3. Energy Efficiency:

  • VFD: By regulating the motor speed in accordance with the required load, VFDs make energy savings possible. VFDs can greatly cut energy usage and boost overall system efficiency by running motors at reduced speeds when full speed is not required.
  • Soft Starter: Soft starters do not provide continuing energy optimisation, although they do assist in reducing the first current surge at motor startup. When the motor reaches its maximum speed, the soft starter is bypassed, allowing it to run at its rated speed while using all of the power necessary for that speed.

4. Cost and Complexity:

  • VFD: Due to its superior control capabilities and capacity to give variable speed control, VFDs are typically more expensive and complex than soft starts. For proper operation, they need extra wiring, programming, and parameter modifications.
  • Soft Starter: Compared to VFDs, soft starts are less complicated and expensive. They are simpler to install and maintain since they require less intricate wiring and setup.

5. Application Suitability:

Variable Frequency Drive (VFD):

  • Motor Speed Control: VFDs are the best choice for situations that call for variable speeds since they provide speed control of AC motors. Conveyor systems, pumps, fans, machinery, mixers, and other devices requiring speed modifications fall within this category.
  • Energy Optimization: By regulating the motor speed in accordance with the required load, VFDs make energy savings possible. VFDs can dramatically minimise energy consumption by running motors at lower speeds when full speed is not required, especially in applications with changing load needs.
  • Process Control: Motor speed can be precisely controlled using VFDs, enabling the control of industrial processes. This qualifies them for applications that call for precise speed, position, torque, and synchronised operation control.


  • Motor Starting: To lessen the first current surge that occurs during motor beginning, soft starters are used. They offer a gradual and regulated ramp-up of voltage, decreasing mechanical strain and the effect on the electrical system. Applications like pumps, fans, compressors, and conveyor systems frequently employ soft starts.

Also Read: Rockwell Automation PowerFlex 4M AC Drive

  • Mechanical Stress Reduction: S starters frequently assist in reducing mechanical component wear and tear by allowing for gentle motor acceleration and slowdown. This can increase device longevity and lower maintenance requirements.
  • Cost-Effective Solution: Compared to VFDs, soft starts are typically easier to use and less expensive. They are appropriate for uses where reduced voltage beginning is sufficient and where a VFD’s continuous speed control is not necessary.

In summary, a soft starter gives decreased voltage beginning to reduce starting current surges, whilst a VFD offers accurate speed control and energy optimization. The application’s particular motor control needs, speed control requirements, energy efficiency objectives, and budgetary considerations will determine which type of starter to use—a VFD or a soft starting.

Asteam Techno Solutions Pvt. Ltd. was established in 2017 with a perspective to become a single-source supplier in Automation industry and is now regarded as one of the top Industrial Automation Parts Suppliers in India. Asteam Techno Solutions Pvt. Ltd. offer you the best products such as HMI, PLC, Power Supply, Servo Motor etc. that we sourced from the trusted brands like Allen Bradley, Siemens, Phoenix Contact, Moxa, Vipa and many more, which give you the maximum possible outcomes.

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