What is the difference between a VFD and a Soft-Start?

Despite frequently being confused as the same device, soft starters and variable frequency drives (VFDs) have extremely different electrical setups and roles. Though they serve similar functions, soft starters are used only for starting up a motor, while VFDs keep motors running at a consistent speed and don’t alleviate startup strain. To find out which device is right for your project, read through our soft starter versus VFD guide below. 

Soft Starters

Soft starters turn an alternating current (AC) motor on and off while alleviating some of the strain on it. A soft start prevents startup inrush currents by using Silicon Controlled Rectifiers to restrict currents based on a motor’s on and off stage. Inrush currents where motors receive full power upon startup risk shocking its components, so preventing damage caused by inrush currents is essential to improving a motor’s life span.

When Should You Use a Soft Starter?

Soft starters should be used on AC electric motors that are compatible with different startup methods. By gradually increasing voltage to the AC motor in smooth acceleration, soft starts increase the product’s life span by preventing inrush currents from harming the motor.

Pros of Soft Starts

When you use a soft starter, you will:

  • Reduce energy use
  • Lower your risk of power surges
  • Adjust acceleration time
  • Reduce the risk of overheating
  • Improve operating efficiency


Soft starters are frequently used in equipment such as conveyor belts, electrical helicopters, fans and pump applications, as these systems require belt pumps and motors with steady progression. 


VFDs are motor controls that convert power frequencies from an input source into a variable frequency. In other words, VFDs control the speed of motors at a certain frequency level. In the U.S., 60 hertz is the common VFD frequency. With additional refinements like encoders and revolvers, VFDs can control shaft positions as well as power frequencies. Though VFDs allow electronics to move smoothly at a frequency, they don’t offer the same surge protection as soft starters.

When Should You Use a VFD?

Variable frequency drive systems are ideal for electronics that need to control the speed of their AC motors, such as blowers, conveyors and pumps. 

Pros of VFDs

For motor systems, variable frequency drives can:

  • Control motor speeds 
  • Control shaft positions with encoders and resolvers
  • Convert input sources to variable frequencies
  • Program known frequencies 
  • Improve motor efficiency
  • Reduce mechanical stress
  • Improve motor life spans
  • Lower motor noise levels 


VFDs see frequent use in compressors, fans and pumps, with these three applications accounting for approximately 75% of all VFD uses. However, VFDs are also useful in small to large motor systems and may be found in conveyors, extractors, extruders and HVAC systems. They’re even used to control helicopter blade speed. 

Find the Right Soft Starter or VFD at Global Electronic Services

Global Electronic Services carries an extensive selection of soft starters and VFDs for all of your business’s motor needs. Our soft starter suppliers include Acco, Bosch, Boston, Feldpausch and Nordic. We sell VFDs from manufacturers including Autocon, Delta, Lovejoy, Met and Robicon. 

No matter the motor or project, Global Electronic Services has components to help your business succeed. Request a free quote from us today.

Call for Help