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Old October 23rd, 2018, 09:18 AM   #9
Gene Bond
United States

Gene Bond is offline
Join Date: May 2004
Location: Indianapolis, IN
Posts: 315
Originally Posted by JeffKiper View Post
I use soft starts on long ramps and heavy load applications. The data that I have been looking at shows that soft starts can handle a greater amount of overcurrent for a longer time vs a VFD.
But, you need to watch for motor heat. For a long ramp time, I've used VFD's to actually save energy and reduce motor heat. For instance, a centrifuge, which may require a 2-3 minute ramp. Some motors can't handle it. Since you can ramp the VFD at 100% motor current, there is no overload condition, unlike the Soft Starter, which runs the motor in it's non-linear area of the curve.

On the other hand, there are loads where you need the extra little bit of motor torque to start, and the VFD has to be oversized, where a properly sized, heavy duty Soft Starter can hit a little harder...
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