Do I Really Need To Use An Inverter Motor

Mike Morehouse

Mike Morehouse

Joined
Jun 27, 2009
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I have an opportunity to get a three phase motor but it is not Inverter rated. I know that Inverter motors are recomended when using a VFD for applications where there are large swings in motor speed, but when grinding I will not be doing constant speed changes. What kind of motor life can I expect if I use a continuous rated motor? Will a premiem efficiancy motor last a little longer? What motor do you use with your VFD?
 
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I't depends a lot on how fast and slow you run it and the service factor of the motor but it should last a long time what brand motor is it, if it is used I would
megar it first and drive it at 60 hertz and you should be fine some have separate fans to help with cooling.
 
Not sure what the brand is, but is made in America and was used on a milling machine. I would assume that it has a high service factor.
 
Inverter-rated motors have spike-resistant magnet wire, Class H (high temperature) insulation, and often thicker varnish (double dipped).

On the other hand, I've run lots of 50 year old motors on VFD's, and they're fine if you don't run the frequency up above 100 hz. I've sometimes had arcing above that.

That's on quality USA motors. I'm not sure I'd want to try that on a cheap Chinese motor, which usually aren't dipped at all.
 
When you slow down a motor on an inverter drive and run it a while, the cooling fan doesn't work as well and the motor gets hot. Inverter grade motors are built to take some extra heat. A non-inverter grade motor should be fine for occasional use on a VFD, or even heavy use if you are running close to 60 hz. It boils down to cost and how you plan to use it...if the used motor is cheap or free might as well give it a try. But...if this is going on an important tool that will run all day every day and downtime will cost you $$$ then a good quality inverter grade motor could be a cheaper choice in the long run
 
I've had no failures so far, running any 3-phase motor of the correct voltage and HP on a VFD. Just my experience, though. I've only personally wired up four. My main grinder motor has been running at varying speeds nearly every day, often hours at a time for a bit over a year. Not inverter duty, but a Baldor industrial motor.
 
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