inverter duty motor - 3 phase for VFD on a disc grinder

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Wanted to get the electrical experts opinions and knowledge on this since I'm still learning about motors.

I wanted to setup my own 9" disc grinder and I did so with my existing KBAC VFD, a 9" Beaumont flat disc and this Marathon motor (AC MOTOR 1.5HP 1800RPM 56C 208-230/ 460VAC 3-PH )
http://www.automationdirect.com/adc/Shopping/Catalog/Motors/AC_Motors_-_General_Purpose_and_Inverter_Duty_(0.25_-_300HP)/AC_Motors-General_Purpose,_Rolled_Steel,_IronHorse_(0.33_-_2HP)/3-Phase_Motors,_56C_(0.33_-_2HP)/MTR-1P5-3BD18

It works however it was brought to my attention that this motor is not inverter duty. In other words when you slow it down (with the VFD), the cooling fan slows down and it can overheat when under heavy load and prolonged use. Maybe it won't ever overheat under practical knife-making use, i.e flattening a blank etc.
I called and spoke to a tech rep at Automation direct.

An inverter rated motor is of course much more $, i.e
here is a comparable inverter duty motor - http://www.automationdirect.com/adc/Shopping/Catalog/Motors/AC_Motors_-_General_Purpose_and_Inverter_Duty_(0.25_-_300HP)/AC_Motors_-_Inverter_Duty,_Marathon_(0.25_-_100HP)/Marathon_MicroMAX_(0.25HP_to_10HP)/Y364

you can see the torque ratings are different ni the 2 motors mentioned.

I searched thru pages of disc grinder motor posts and saw many suggestions of motors to use, but I did not see one mention of an inverter duty rated motor.
In fact, it appears that many of the disc grinder manufacturers motors are not inverter duty rated, hence keeping the price of the total disc grinder down.

Am I making something out of nothing here? :-)
 
Unless you plan on doing slow speed sanding for long periods of time, it will be fine. The best way to deal with heat up is to check the motor casing every now and then. If it is hot, turn the motor to high speed and let it spin for a minute to cool the windings down. Normally, knifemakers done run their disc sander motors for long enough periods to overheat.
 
ok so as I suspected, the practical use doesn't warrant the $ need for an inverter duty motor,
and in fact Stacy, that is what the tech rep told me, check the motor to see if it's heating up
thanks
 
From the first motor you linked, if you will check the spec manual you'll find:
• Inverter capable (3-phase only)
• NEMA design B
• Class F winding insulation
• Service Factor: 1.15 across-the-line (1.0 for 3-phase with AC drive)

As you can see, the motor is spec'd for VFD work, but you do have to drop the SErvice Factor rating to 1.0 - as Stacy says, just check on the motor case from time to time and "IF" you find it too hot to comfortably hold your hand on, run at high speed a few minutes to cool.

Ken H.
 
Even inverter rated motors can overheat if run slow enough and long enough. In industry this is solved by an external bolt-on fan kit. I don't think I would go to the trouble because of what Stacey has stated, but if you are concern just put a small house fan blowing into the impeller.
 
I didn't post it because it is pretty redundant, but a $5 axial/pancake fan from an old computer or such will work fine if you are concerned.
 
I wouldn't be concerned as long as your not planning on using it in a production environment. I run that exact motor on a variable speed 2x72 GIB every day and don't have any problems. The housing never gets the slightest bit warm.
 
Thank you all for this. I run my disc grinder at about 25% virtually all the time. I will now for sure check for heat on the motor casing.
It might save me a big problem.
Frank
 
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