Skip to main content

Variable Frequency Drives vs Soft Starters: What’s the Difference?

Posted by Mechtric on 25th Mar 2026

Electric motors are widely used in industrial applications to power equipment such as pumps, conveyors, compressors and ventilation systems. When starting and controlling these motors, engineers often need to decide between two common technologies: variable frequency drives (VFDs) and soft starters.

Both devices are designed to improve motor starting and protect electrical systems, but they serve different purposes and provide different levels of motor control.

Understanding the difference between VFD motor drives and soft starters helps engineers select the most suitable solution for their application.

What is a Variable Frequency Drive (VFD)?

A variable frequency drive (VFD), also known as a variable speed drive (VSD) or AC motor drive, is an electronic device that controls the speed and torque of an electric motor by adjusting the frequency and voltage supplied to the motor.

By varying the motor speed, a VFD allows equipment to operate at the optimal speed required for the process.

Variable frequency drives are widely used in applications such as:

  • pump control systems
  • conveyor systems
  • ventilation fans
  • compressors
  • industrial automation equipment

VFDs provide continuous motor speed control, making them ideal for applications where motor speed must change depending on system demand.

What is a Soft Starter?

A soft starter is an electrical device designed to reduce the mechanical and electrical stress that occurs when starting an electric motor.

When a motor starts directly across the line, it can draw a very high inrush current. A soft starter gradually increases the voltage applied to the motor, allowing it to start smoothly.

Soft starters are typically used in applications where the motor runs at a constant speed once it has started.

Common soft starter applications include:

  • compressors
  • crushers
  • conveyors
  • large fans
  • pumps that operate at fixed speed

While soft starters improve motor starting, they do not provide speed control once the motor reaches full speed.

Key Differences Between VFDs and Soft Starters

Although both technologies improve motor starting performance, they differ significantly in functionality.

Feature

Variable Frequency Drive

Soft Starter

Motor Speed Control

Yes

No

Energy Efficiency

High (adjusts speed to demand)

Limited

Motor Starting

Smooth acceleration

Smooth acceleration

Process Control

Excellent

Limited

Application Flexibility

Very high

Moderate

The main advantage of a variable frequency drive is its ability to control motor speed during operation, while a soft starter primarily improves the starting process.

When to Use a Variable Frequency Drive

A variable frequency drive is typically the best solution when motor speed needs to be controlled during operation.

Common applications include:

  • pump systems with variable flow demand
  • HVAC fan systems
  • conveyor systems with adjustable speed
  • mixing and agitation equipment
  • irrigation pumps

In these applications, adjusting motor speed reduces energy consumption and improves process control.

Drives such as the Delta MS300, C2000+ and CP2000 series are commonly used for these types of applications.

When to Use a Soft Starter

Soft starters are typically used when a motor only needs a controlled startup but will run at full speed once operating.

Typical soft starter applications include:

  • crushers
  • large compressors
  • fixed-speed conveyor systems
  • heavy machinery with high starting loads

In these cases, the primary objective is reducing starting current and mechanical stress rather than controlling motor speed.

Energy Efficiency Considerations

One of the biggest advantages of variable frequency drives is their ability to reduce energy consumption.

For applications such as pumps and fans, reducing motor speed even slightly can significantly lower electricity usage due to the Affinity Laws, which state that power consumption decreases dramatically as motor speed decreases.

This makes VFDs particularly effective in industries looking to reduce operational energy costs.

Delta Variable Frequency Drives from Mechtric

Mechtric supplies a range of Delta variable frequency drives designed for industrial automation and motor control applications.

Available Delta drive series include:

These drives provide advanced motor control, energy efficiency and reliable performance across a wide range of industrial environments.

Choosing the Right Motor Control Solution

Selecting between a variable frequency drive and a soft starter depends on the requirements of the application.

If the goal is simply to reduce starting current and mechanical stress, a soft starter may be sufficient. However, if the application requires motor speed control, improved energy efficiency or process flexibility, a variable frequency drive is usually the better solution.

Speak to Mechtric About Delta Variable Speed Drives

If you are evaluating motor control solutions for pumps, conveyors, fans or automation equipment, the Mechtric team can assist with selecting the right Delta drive for your application.

Contact Mechtric to learn more about Delta variable frequency drives and find the best solution for your motor control system.



!