Soft-Starters versus VFDs: Another Look

AC Motor Softstarter Soft Starters versus VFDs: Another Look

AC Motor Soft-starter

Both soft-starters and variable frequency drives (VFD) are used to control the torque, load and speed of the motor. But the main difference between them is that soft-starters do it temporarily by reducing the mechanical stress on the motor or shaft whereas the VFD controls it by varying the input frequency and voltage. The functions are almost same but some of the features that are different have been discussed below.

To start a motor, pump, compressors, mixtures etc. there are only two choices: soft-starter and VFDs. Both of them perform the same task but with a slight difference.

  • A VFD can be replaced by a soft starter in a way that if someone does not want to vary the production speed of the motor, then variable frequency drive is the device that can be used because soft starter’s cost is less than that of variable frequency drive.
  • VFDs can vary the output frequency from zero to above base motor frequency in order to maintain the pressure and flow in various operations. In comparison to soft starter, VFDs offers larger analog and digital diagnostic signals for greater automation of the processes.
PH.A1000 Soft Starters versus VFDs: Another Look

Yaskawa’s A1000 VFD

Soft-starters and VFDs are both energy-efficient. They save about 30%-50% of the energy that results in the low-cost involved. However, the efficiency is different in both the devices when compared. VFDs provide more benefits than soft-starters but their cost is very high and efficiency is lower than soft-starters which are around 99% efficient as compared to variable frequency drives that are 93%-95% efficient. VFDs are considered to be the best for the small machinery like small pumps and small mixtures as they save a lot of energy, but when VFD’s work with larger machines, higher amount of energy is consumed.

So, soft-starters are designed for large equipment as they are energy-efficient and they do not hinder the speed of machine. They can even reduce the mechanical and electrical shocks that may occur as industrial process outcome. This is so because large machines require no stops or integrations of any kind. Apart from saving energy, there are some other tasks also that are performed by both of them like reducing noise in the machines, reducing amps when the motor gets started, demand charges are lowered that reduces the bill of electricity, accurate controls for HVAC settings and many more.

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