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Old October 24th, 2018, 10:27 AM   #13
dwoodlock
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Join Date: Nov 2012
Location: South Carolina
Posts: 413
We had an application where a siemens soft start was being used with a 48" centrifugal fan driven by a 25hp motor.

This was my first experience with a soft start, but after the second failure. we ended up replacing it with a very basic siemens VFD. Cost wise the VFD we purchased was about 50% less than the soft start, which was shocking to me.

Luckily the panel had plenty of room so we were able to fit the VFD which was probably 4 times the size of the soft start. Still not real sure why the soft start would periodically go bad. As I recall the first one lasted about 3-4 years and then the second only 2.

When the first one failed we tripped the 250amp breaker that fed the machine. We started noticing strange occurrences around that time before it finally bit the dust. Second time, we started noticing some of the strange occurrences again, and decided to yank it in favor of the VFD after again checking the motor.

VFD has been in service about 9 months now with the same motor and fan without any issues, we'll see if we get better results in the long run.

Anyone ran into something like this?
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