# Best 3 phase motor for VFD's



## mrbreezeet1 (May 24, 2013)

I was going to try to scrounge up an old 3 phase motor for my metal lathe, maybe 1/2 HP.
Someone said the new motors are designed for VFD's, and I would be better off buying a new motor.
Is this true, and are all new 3 phase motors designed for VFD's, of just some of them?
Thanks,
Tony


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## itsme_Bernie (May 24, 2013)

I don't know if new motors are "designed" for them.

With any used motor it is a crap shoot.  My really old motor from my old Rusnok head was whisper quiet.  My newer (used) Baldor motor sings a high pitch (could be the motor, could be some settings I'm working on)

My old SB has a pretty quiet motor, and that us really old!  

Bernie


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## Ray C (May 24, 2013)

Leeson makes decent, affordable motors based on my experience and it's the brand of motor that Matt (from Precision Matthews) recommends when folks convert his equipment.  I have 3 of them.  The instructions come with a packing slip addendum which mentions minimum frequency of 30 to 60 Hz.  I don't know if all new motors are this way but, I do know that much older motors had problems with overheating when run at lower speeds.  Motors like this are typically TEFC (Totally Enclosed Fan Cooled).  The fan is on the outside and blows air past the cooling fins on the case.  At lower RPMs the older motors did not have  enough air circulation to cool them.

That said, I have a motor that's probably 60 years old on my surface grinder.  It is open cage and it does fine on VFD which I operate at speeds from about 2000 to the rated 3600.


Ray


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## mrbreezeet1 (May 24, 2013)

Oh, he says no more than 30 to 60?
I run my wood lathe lower and higher than that, but have not run it for too long at those HZ's. I have run it down at 5 HZ to brush on a finish, lets say.

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Wish l still had the 2 motors I tossed 10 years ago.
One off a delta bandsaw, and 1 off my Oliver wood lathe. 
Kept them around for a while, but tossed them when I moved.


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## Ray C (May 24, 2013)

If you're running at very low RPM and not putting a great strain on the motor, I think you'll be fine.  I would not run it down real low and try to drill a hole.  In that case, I'd increase RPMs and use the gears to get the torque.  The VFD on my lathe is set to only allow operation between 40 to 60 RPM.  If I can't get the R's I'm looking for, I switch gears.

I would not consider running a motor at speeds higher than 60 Hz (or whatever the instructions indicate).


Ray





mrbreezeet1 said:


> Oh, he says no more than 30 to 60?
> I run my wood lathe lower and higher than that, but have not run it for too long at those HZ's. I have run it down at 5 HZ to brush on a finish, lets say.


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## mrbreezeet1 (May 24, 2013)

I got this set-up on my wood lathe. Works off 110 volt, I like that. 
Working pretty good, but don't know how the import motor will hold up?
http://dealerselectric.com/item.asp?cID=0&PID=6898

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Did you mean 40-60 HZ?



Ray C said:


> If you're running at very low RPM and not putting a great strain on the motor, I think you'll be fine.  I would not run it down real low and try to drill a hole.  In that case, I'd increase RPMs and use the gears to get the torque.  The VFD on my lathe is set to only allow operation between 40 to 60 RPM.  If I can't get the R's I'm looking for, I switch gears.
> 
> I would not consider running a motor at speeds higher than 60 Hz (or whatever the instructions indicate).
> 
> ...



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Am thinking about going with the same set-up I have on the wood lathe, 1/2 hp is enough for a 10" logan right?
http://dealerselectric.com/item.asp?cID=0&PID=6898


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## Ngray (May 24, 2013)

This doc has a good explanation of why an "inverter duty" motor is more tolerant of VFD's:

http://www.automationdirect.com/static/specs/motorsselection.pdf


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## mrbreezeet1 (May 24, 2013)

Wonder if the one I linked to is really a inverter duty?
http://dealerselectric.com/item.asp?cID=0&PID=6898



Ngray said:


> This doc has a good explanation of why an "inverter duty" motor is more tolerant of VFD's:
> 
> http://www.automationdirect.com/static/specs/motorsselection.pdf



_*Edit, 
Actually I got the 3/4 hp for my wood lathe. *_


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## Ngray (May 24, 2013)

Hard to say, but here's the data for that motor:
http://www.dietzelectric.com/documents/Brook 2009 Catalog.pdf

For 160, it looks like a smokin deal.


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## mrbreezeet1 (May 24, 2013)

Dealers electric said in there FAQ, 
"Most 3 phase motors made today are inverter duty"
No, actually it says,

_Q. Do I need a special VFD rated motor? __
A. If you already  have a motor use it, you can always change it later. *Most motors  manufactured today are rated for use with a VFD*. Some models will allow  you a greater range of speed than others. You can always contact us to help with your selection._



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_*You guys think 1/2hp is enough, or should I get the 3/4hp again.*_


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## Ray C (May 24, 2013)

Yes, a typo indeed.  40-60 HZ.  This is self imposed as I'm a firm believer in using the gears as much as possible and only tweaking RPMs to suite a particular need.  This (I feel) keeps the motor working in a decent torque range and does not place undue stress on the gear train.

The lathe and mill motors are 4 pole which have high-end RPMs of just under 1800 RPM.  2 Pole motors (usually used on surface grinders) will spin up to 3600.


Ray



mrbreezeet1 said:


> I got this set-up on my wood lathe. Works off 110 volt, I like that.
> Working pretty good, but don't know how the import motor will hold up?
> http://dealerselectric.com/item.asp?cID=0&PID=6898
> 
> ...


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## mrbreezeet1 (May 24, 2013)

Ngray said:


> Hard to say, but here's the data for that motor:
> http://www.dietzelectric.com/documents/Brook 2009 Catalog.pdf
> 
> For 160, it looks like a smokin deal.



Yeah, I don't know how they are doing it, I see that motor alone for $166.00-$177.00.
You have to add $40.00 to dealers electric for shipping though.


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## Ngray (May 25, 2013)

mrbreezeet1 said:


> Yeah, I don't know how they are doing it, I see that motor alone for $166.00-$177.00.
> You have to add $40.00 to dealers electric for shipping though.



Is that vfd solid? I didn't even look hard at it.


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## mrbreezeet1 (May 25, 2013)

Ngray said:


> Is that vfd solid? I didn't even look hard at it.



I don''t know, it seems OK. I hadn't any prior experience. 
Turn you system volume down first.
http://www.youtube.com/watch?v=PtWUIV9zFO0


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## lens42 (May 25, 2013)

I've done many 3-phase/VFD conversions (about 10) and I've never had a problem with any motor, nor have I ever seen a posting on a forum from someone who has personally had a problem with any 3-phase motor on a VFD. In an industrial high-duty-cycle and maybe high-temperature environment, you might need to be more careful and worry about an inverter rating, but in a home shop, use whatever you can get with the HP rating you need at the best price you can get. I've had great luck with 1/2 to 1/5 HP motors on eBay. I don't think I've ever paid more than $100 with shipping for Leeson, Reliant, and other good brands.



mrbreezeet1 said:


> I was going to try to scrounge up an old 3 phase motor for my metal lathe, maybe 1/2 HP.
> Someone said the new motors are designed for VFD's, and I would be better off buying a new motor.
> Is this true, and are all new 3 phase motors designed for VFD's, of just some of them?
> Thanks,
> Tony


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## mrbreezeet1 (May 25, 2013)

anybody ever get a good one at a scrap yard?


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## lens42 (May 26, 2013)

mrbreezeet1 said:


> anybody ever get a good one at a scrap yard?



Around here (nor CA) the scap yards charge more than eBay. Search "1/2 HP 3-phase motor" and sort cheapest first. There are several under $70 with shipping, and some look new.


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## mrbreezeet1 (May 26, 2013)

Yeah, I don't know what this scrap yard here sells them for. I know they only gave me about $3.00 for a motor I took there.
I heard he is tough too.
If I am going to pay $70.00 for just a motor, on e bay, I might as well get the TEDCO brook Compton deal for about $200.00 shipped.

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see, I have this Idea, the cheaper I can put this stuff together for, the more fun it is. 
I better just get that out of my head, cause I'm not having any fun lately.


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## Kroll (May 26, 2013)

http://dealerselectric.com/item.asp?PID=6898 
Brand new and a warranty---kroll


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## mrbreezeet1 (May 26, 2013)

Kroll said:


> http://dealerselectric.com/item.asp?PID=6898
> Brand new and a warranty---kroll



Yeah, thats the one I have on my wood lathe. 
They told me only 90 days on the motor, but I thought I saw elsewhere 2 years on the motor.

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90 days made it seem like they did not have much faith in it.


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## Kroll (May 26, 2013)

That stinks,must have had problems in the past with those motors---kroll


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## rdhem2 (Aug 11, 2013)

VFD's are hard on motors because while they operate they flash high voltages to the motor windings as part of the control scheme.  On older motors and those not rated for VFD use the problem comes from insulation break down due to these high voltages.  The voltage blows a hole in the insulation and the motor shorts phase to phase or phase to ground and burns up.

Speed Issues;

Too high a speed, those over 60Hz.  The motor bearings and bearing housings are not rated and designed for operating at over nameplate speeds.  Also the dynamic balancing of the rotor is not usually adequate for excess speeds and you will loose the rotor to armature air gap ( a few thousands) the rotor then drags and you are out of business.

Too low a speed, those under usually 25 to 30Hz on a motor not designated for vfd applications.  Ray C is to be commended for his conservative operating practices.  Operating below these levels the cooling fan on the motor looses its effectiveness and the motor overheats.  When the motor overheats the windings burn out even though the motor is not overloaded electrically.  The heaters in the overload or thermal device don't have a clue.  Running your motor under a light load for a short period of time will _probably_ never hurt a thing.  I used to have problems with mechanics turning the speed down on motors instead of changing the gearing.  Then I started setting the slow limit to 25Hz and made the mechanics mad but management happy when they stopped burning out motors.

Life is never simple, or so it seems.


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