# VFD on general purpose motor



## ponyboy (Nov 18, 2012)

anyone done it? i have an exhaust system for some lasers and the fan load is changing. the mechanical contractor says the original setup is moving too much air and something needs to be done or the spiral ductwork will just collapse when turned on. the manufacturer of the exhaust system reccomended putting the motor on a VFD. i looked at the motor and it is not an inverter duty type. i know there'd be major issues if we were speeding the motor up but it will be running slower now which should help with any overheating issues. i'd prefer just replacing the motor with a new super-E but honestly its not going to be my call. if there's anything anyone wants to add im all ears because i'd love to be able to save some money and avoid pulling this motor out in a year if thats the case.


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## Wirenuting (Sep 12, 2010)

It will last with few issues. As long as everything else is in good shape, you should be good to go. 

If you want, up sell the E. but IMO, you don't need to.
I have hundreds here and they weren't replaced when the drive wave swept thru.


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## Rollie73 (Sep 19, 2010)

I have 2 AHU's which are running VFD's on regular duty motors in the nursing home I do maintenance on. 
No problems so far (4 yrs and counting)but I'm waiting and counting the money for changing them out.:thumbsup:

You should be ok for quite awhile.


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## Jlarson (Jun 28, 2009)

Yes.

Ask the manufacture if they have any recommendations on settings for the drive. Like for submersable pumps they have recommendations in their install manuals. 

Usually you can just run them till they eventually die then put a new inverter motor in then.


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## JRaef (Mar 23, 2009)

Usually it's OK, at least for a while. I always tell people that if you already have the motor, no need to swap it out as long as it works. But when it does die, _replace_ it with an "inverter duty" motor. The only thing to consider is the cost of down time, because Murphy's Law is always true; when it does fail, it will be at the worst possible time.

You can take some simple steps to help protect it though; a load reactor at the very least, but for a few dollars more you can make it a load filter. That will help prevent some of the insulation damage that can occur and reduce the bearing damage issues. Also, just make absolute sure you either run steel conduit, properly bonded to ground, or run shielded VFD cable if that is impossible.


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## NJELEC (Oct 19, 2010)

We have done this and have had motors fail within weeks and some last a while. As mentioned above placing filters in line is the way to go if the motors are to remain. The projects we have done that filters are installed ......no issues


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## triden (Jun 13, 2012)

Two things to keep in mind when running general purpose motors on VFD's

1.) Do not run the motor slowly. The general purpose motors will overheat as the fan is designed to cool best at full speed. Inverter duty motors can handle the heat from running at lower speeds.

2.) Insulation break down. VFD's give off harmonics that can sometimes double the voltage seen by the motor. This is intensified by the length of the feed cables and will cause the insulation to break down in short order.

It's possible that an extreme duty motor will last longer than a normal duty motor, but I wouldn't put a warranty on it


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## ampman (Apr 2, 2009)

i know of two that are on a conveyor system for over 20 years, i guess they don't make them like they used to


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## Peewee0413 (Oct 18, 2012)

Uh huh, limit the airflow.


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## don_resqcapt19 (Jul 18, 2010)

If the amount of air to be moved does not have to be changed, I think I would look at a damper before I looked at a VFD.


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