Choosing between a soft starter and a VFD to fit your application

By K Danielson, Eaton


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Published in:

Electricity+Control, July 2013 (pages 4 – 6)



Soft starters are used in applications where:

  • Speed and torque control are required only during start-up (and stop if equipped with soft stop)
  • Reducing large start-up inrush currents associated with a large motor is required
  • The mechanical system requires a gentle start to relieve torque spikes and tension associatedwith normal start-up (for example, conveyors, belt-driven systems, gears, etc)
  •  Pumps are used to eliminate pressure surges caused in piping systems when fluid changes direction rapidly

Variable frequency drives (VFDs) are used in applications where:

  • Complete speed control is required
  • Energy savings is a goal
  • Custom control is needed


Take note

  • The choice of either a soft starter or a VSD depends on the application.
  • A VSD has the benefit of being able to ensure more efficient motor operation.
  • Lifecycle costing, including energy usage, must be factored into the decision as to which is the best choice.