The Differences Between Variable Frequency Drives and Soft Starters for Motion Control Applications

Motion control applications often require delivering large amounts of energy to a motor for quick acceleration. Soft starters and variable frequency drives (VFDs) are both used to control this inrush of energy when starting or stopping a motor, but there are great differences between the two.

Oftentimes, VFDs and soft starters help achieve a desirable motor speed or torque for a given application, as well as protect the mechanical integrity of the motor over time. Both can be critical components for motion control and understanding the differences between both can help you know which is best for your application.

How VFDs and Soft Starters for Motion Control are Different

Soft starters are solid-state devices that protect AC motors from damage during startup or stopping. They work by limiting the initial inrush of energy to the motor and gently allow it to ramp up to full speed. This allows for a gradual startup to eliminate torque spikes that could be detrimental to an application, such as on conveyor or belt-driven systems.

VFDs differ from soft starters but have a similar mission of protecting a motor from damage and offering speed control. VFDs provide speed control for motors during the startup and stop cycles, in addition to the run cycle, whereas soft starters are typically only used for startup . VFDs convert input power to adjustable frequency for complete speed control of AC motors.

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The Roles of VFDs and Soft Starters

Soft starters are a more basic solution than VFDs. Soft starters are typically used when speed control is only required during the startup of a motor and the rest of the time the motor runs uninhibited at full speed. The primary goal is the protection of the motor.

VFDs are a more comprehensive solution – they’re used when complete, custom speed control is required throughout the entire operation of the motor. While protecting the motor is an important part of what a VFD offers, it can also lead to significant energy savings by effectively managing the motor’s energy consumption.

VFDs and soft starters play similar roles in motion control applications but function differently. Their primary difference lies in the level of speed control they offer. Understanding these differences and knowing the type of motion control required in your application is essential for choosing the right speed control solution.