Home Construction Choosing a Soft Starter or a VFD

Choosing a Soft Starter or a VFD

by Tim Morris
variable frequency drive

When choosing between a soft starter or a VFD for your motor, there are many different variables that come into play. Ultimately you’ll want to make a choice that is economical, but also makes sense in the long-run. In this article we’ll break down the core differences between the two and help you make the most informed decision possible.

Soft starters

Motors require a large amount of energy when accelerating up to their full speeds, and this can often lead to long-term damage and frequent performance issues.

Soft starters are used to protect motors from these sudden rushes of power by reducing the inrush currents and limiting torque. This can help protect equipment from further damage, extend its lifespan and reduce motor heating.

They work by reducing voltage and output via reducing torque. Often they use solid-state devices to control the flow of the current. They can control one to three phases, with the most effective being the three-phase control.

Soft starters are the most affordable option for products that only require speed and torque control during motor startup. They also are quite compact and are an appealing option when space is a concern.


A VFD (variable frequency drive) is a motor control device that controls and protects the speed of an AC induction motor. While soft starters only work during motor startup, VFDs are able to control the speed of a motor during the run cycle as well as the start and stop.

VFDs work by converting the input power to adjustable frequency and voltage source in order to control motors. One of their biggest selling points is the amount of energy that they save, and the reduction of power consumption that comes along with that. The adjustable flow method they utilise changes the flow curve and offers the greatest energy savings for pumps and fans.

Soft starters vs. VFD drives

Choosing between soft starters and VFDs depends on your application and what you wish to get out of the product. The main difference between the two is the amount of control each one offers. Soft starters control only the stopping and starting of a motor, whereas VFD drives can vary the speed throughout the entire run cycle.

While soft starters have their smaller, compact size as well as affordability on their side, VFDs are required when more speed control is necessary. Although they are more expensive upfront, VFDs may end up being the most affordable option due to the energy-saving processes they implement.

18% of the energy used across the 40 million motors in the US could be saved by energy-efficient products such as VFDs, demonstrating their efficiency and importance in today’s world.

VFD’s can also offer a higher level of functionality than soft starters, such as digital diagnostic information.

It’s important to make the best decision for your application when deciding between a soft starter and a VFD. Although you want to be economical, make sure you are thinking about the future and what product best aligns with your needs and objectives of this purchase.

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