Grinder motor advice

D

Dave Hub

Joined
Dec 10, 2014
Messages
57
So I was just about to pull the trigger and start buying some parts for a 2x72 grinder. The motor I had my sights set on was the Iron Horse 2HP 3600rpm https://www.automationdirect.com/ad...-Phase_Motors,_56C_(0.33_-_2HP)/MTR-002-3BD36

Apparently, it is now listed as "obsolete" on the website.

Does anyone have any recommended alternative? What about the same motor at 1800 rpm? My plan was to run a VFD with it (either Teco or Kbac).

Dave
 
Yea, many folks actually prefer the 1800 rpm motor. I went with the 3600 rpm because it was less expensive and got my desired 4,000 SFPM belt speed without using the doubling method on VFD. There is nothing wrong with doubling the 1800 RPM motor and running it 120 hz to get the 3600 rpm motor. Some folks say you have more torque with this method at the low RPM, but at low RPM you really don't need the extra torque.

I sure hate to see they've dropped the 3600 rpm motor in case I ever need a replacement. $126 shipped was a very good price.

I was going to send this link via email so it wasn't spread around so much, but you don't have an email listed so you'll lhave to take your chance getting this before it's gone. A Leeson 2hp, 3ph 56C motor for $131 shipped:
http://www.ebay.com/itm/391610070353?

edit: I see it is TENC rather than TEFC enclosure. I suspect for normal grinder use that would be ok. The fan cooling would be required for running at 2 hp load for long periods, but for grinding it will seldom see more than 20 to 50% load for more than a few minutes. I'll be interested to see other comments on the suitability of TENC motor vs TEFC.

Ken H>
 
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Thanks Ken.

Quick follow up question. How do you double up an 1800 rpm motor? Do you need to re-wire it?
 
Using a VFD will allow you to double the Hz. I wouldn't worry about that though. I have that exact motor in the (3600rpm) and seldom run at full speed (60Hz) I hover around 35/40 at most for profiling my knives. The rest is high 20's. you'd be happy with the 1800rpm.
 
I double an 1800 on mine. It's just a setting in your vfd. You set the min and max frequency in Hz that you want the vfd to generate in the range of your potentiometer. Oddly I had to set my vfd to a max of 200 Hz in order to get 120 but I'm guessing my pot is causing that.
 
You may be able to get a nice US-made motor on Ebay for a lot less. I paid something like $135 shipped, for a Reliance 3HP 1800-RPM motor in great condition. I would never buy a new Chinese motor if I didn't have to.

I did a lot of research on the RPM thing. Here is what I (sort of) concluded. The bearings will go over 14000 RPM, so speeding up to 3600 or so won't hurt them, apart from reducing the lifespan by increasing wear. The guts of the motor are probably made to the same specs as 3600-RPM motors, because it would be a pain for manufacturers to go to the trouble of making weaker stuff for 1800 RPM's when they can just use the same parts they use for 3600. I figure that if you're overspeeding an 1800-RPM motor, you're really overspeeding something made to run all day at 3600.

If you get a motor made for 1800, presumably, the fan will be appropriate for that speed, so you're not overheating the motor if you choose to run it at nameplate speed. I don't know if that would be true of a 3600-RPM motor fan.

I'm not an expert, but nothing has exploded yet.
 
Ken H> said:
Yea, many folks actually prefer the 1800 rpm motor. I went with the 3600 rpm because it was less expensive and got my desired 4,000 SFPM belt speed without using the doubling method on VFD. There is nothing wrong with doubling the 1800 RPM motor and running it 120 hz to get the 3600 rpm motor. Some folks say you have more torque with this method at the low RPM, but at low RPM you really don't need the extra torque.

I sure hate to see they've dropped the 3600 rpm motor in case I ever need a replacement. $126 shipped was a very good price.

I was going to send this link via email so it wasn't spread around so much, but you don't have an email listed so you'll lhave to take your chance getting this before it's gone. A Leeson 2hp, 3ph 56C motor for $131 shipped:
http://www.ebay.com/itm/391610070353?

edit: I see it is TENC rather than TEFC enclosure. I suspect for normal grinder use that would be ok. The fan cooling would be required for running at 2 hp load for long periods, but for grinding it will seldom see more than 20 to 50% load for more than a few minutes. I'll be interested to see other comments on the suitability of TENC motor vs TEFC.

Ken H>
Click to expand...

By the looks of the plate too, the shaft dia is "special" so you might have to get a custom pulley made. I'd be weary about that, also looks a little short too.
 
Edit to change post completely!!

I didn't check the shaft, and looking at this motor: http://www.ebay.com/itm/391428527883?

Which seems to be almost the same motor except for the 460 vac, it shows the shaft is NOT the standard shaft. I might just pass on that motor I linked to without checking with vendor. Marc, Thanks for noting the shaft.
 
The Mighty Ginsu said:
You may be able to get a nice US-made motor on Ebay for a lot less. I paid something like $135 shipped, for a Reliance 3HP 1800-RPM motor in great condition. I would never buy a new Chinese motor if I didn't have to.

I did a lot of research on the RPM thing. Here is what I (sort of) concluded. The bearings will go over 14000 RPM, so speeding up to 3600 or so won't hurt them, apart from reducing the lifespan by increasing wear. The guts of the motor are probably made to the same specs as 3600-RPM motors, because it would be a pain for manufacturers to go to the trouble of making weaker stuff for 1800 RPM's when they can just use the same parts they use for 3600. I figure that if you're overspeeding an 1800-RPM motor, you're really overspeeding something made to run all day at 3600.

If you get a motor made for 1800, presumably, the fan will be appropriate for that speed, so you're not overheating the motor if you choose to run it at nameplate speed. I don't know if that would be true of a 3600-RPM motor fan.

I'm not an expert, but nothing has exploded yet.
Click to expand...

Yes. As I've said in other threads, I previously worked in a Regal Beloit plant (Leeson) and there is mechanically no difference between a 3600 and 1800 rpm motor. The only difference is the windings, and because of that slight differences in the stators, but mechanically speaking, a typical 56 sized motor of X hp has the same bearings, same shaft, same endbells, same everything, other than different windings and if I recall correctly I don't even think they got different fans unless it was a motor for a particular duty in mind.
 
Shucks, if they've got the same fan, then the 3600 rpm motor is going to cool just as well at half speed as the 1800 rpm motor will at full speed. As I've mentioned before, I purchased the 3600 rpm motor because it was less expensive - I think either rpm motor is going to work just fine for grinder use.

Ken H>
 
I don't believe cooling to be an issue at 1800+ rpm with either motor. Sub speed, like 900rpm at high load is where you might cause heat problems, which isn't a problem for us because if we're using low speed we're most likely using low pressure.
 
I would think higher HP would lead to cooler performance, since motors get hot when you strain them.

So far I haven't been able to get my motor's case warm.
 
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