Shopping for a DC motor

W

Wapiti

Joined
Sep 25, 1999
Messages
483
I am beginning to shop for a DC motor in earnest. Time to upgrade. Hoping to build a grinder in the next year, and plan to rebuild my Grizzly and use the DC on it for the meantime. I have considered step pulleys, but after hours of calculations and thinking, I would have to decrease the size of my drive pulley significantly on my Grizzly in order to get to manageable speeds, and I think I would be better off going with DC.
Then I can always switch the DC to my new grinder when I finish it.
I wanted to ask you all if you could give me any pointers and answer some questions. I have a few sources for buying new, and all seem pretty pricey. Anyone have a source for purchasing new motors at great prices? I plan to camp out on Ebay, understand many have gotten great setups there. I also have access to the surplus machinery catalog and a place called Roys Store. Any other places you would recommend checking out?

This what I know.
I have a controller rated for max 2HP, so that is what I would like to get. I know I need a permanent magnet motor that will run 220V.

Here are my questions.
Are there any brands I should avoid? I know Leeson and Dayton are pretty good.
Are all DC motors reversible, or should I look for this feature?
Any reason I should pass on used or rebuilt motors? I thought about checking out my local motor shop, and seeing what he has in rebuilt motors. If you would recommend used/rebuilt, what sorts of tricks can I use to make sure I am not getting an anchor?
Does the frame config matter if I am going to use a pulley?
Which max speed would you recommend? I was going to get 1725rmp, but was wondering if I should consider 3500rpm. With a 4" or 8" drive wheel, that is some serious fpm! But if I get a higher max rpm, will I still have as much fine tune control for the slower speeds, finer belts, etc.?
Is there anything else I don’t even know I don’t know?

Lastly, if anyone out there has a motor, or knows someone who does, and wants to sell, I am very interested. It would really help me out.
Thanks for all your help.
Brome
 
Brome,

Make sure your motor matches your controllers DC output rating (e.g., 180V DC, 100V DC).
I've owned DC motors from Leeson, Baldor, and Reliance. All gave me good service, although I didn't use the Leeson all that much.
You can reverse the direction of the motor by reversing the output leads. For practical purposes, you would want a reversable controller if you want the ability to change directions often.
Two of my motors were used and in good condition. If you are able, have the seller run the motor and ask to see the brushes/armature under the inspection covers.
You can get frame descriptions from the motor manufacturers and I think Graingers has a list of them. Make sure the one you are looking at fits your needs.
I would stay with a motor that is under 2500 rpm. I suspect that some of these faster motors are not as heavy duty and rely on speed to boost their HP rating, but I could be wrong.
Your controller will allow you to dial down to zero, if you have your pots set that way. Torque may be an issue with some motors though.
I would try to find a 2 HP motor, and would settle for a 1.5 HP, if the price is right. You could always use it for something else later, such as a disk grinder. I've settled for a 1 HP motor in the past, and I could stop it without even trying. I now have a 3 HP shunt wound Baldor and it's like trying to stop a tank. :)
Check your local dealers so you know the going rate and then look around. I know one of my local dealers sells at approximately 70% of the retail price.
 
Thanks for the informative reply, Brett.
I have one more question. What is the difference between shunt wound and permanent magnet DC motors? Is this an important consideration when I am purchasing a motor? How do I know if my controller will run either type?
Thanks again,
Brome
 
Brome, in laymans(me)terms, shunt wound motors are somewhat bigger in diameter than permanent magnet. They also seem to have way more torque.
I have both in my shop, the shunt wound 11/2HP has 37 foot pounds of torque, listed on the nameplate, my permanent magnet has 57ft., lbs. listed. Despite the labels, the shunt wound, has way more useable torque. You can hook up either to your controller.
 
Brome,

From what I understand, the shunt wound is the better of the two and seems to be more common in higher HP ratings.
Shunt wound motors have field windings in addition to the normal current leads. I don't know much more about them other than your controller will need to have the outputs for field leads if you get a shunt wound. I just went through this drama recently and, three controllers later, I have the correct one for the shunt wound I mentioned earlier.
Perhaps an industry professional can offer some more insight. Most of what I know is from trial and errror. :)
 
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