Grinder motor NEMA specs confusion...

D

DAVEW252

New Member
Hey, folks! Building my first 2x72 grinder here. (The NWGS). I need to do it on the cheap.
I'm planning to just do the belt-and-3-step-pulley setup as in the plans.

I found these two motors, in my price range:


http://www.automationdirect.com/adc...-Phase_Motors,_56C_(0.33_-_2HP)/MTR-1P5-1AB36
and
http://www.automationdirect.com/adc...Phase_Motors,_56C_(0.33_-_2HP)/MTR2-1P5-1AB36


They are slightly different dimensionally. The only other significant spec difference I see is that one is what they are calling "NEMA Design L" and the other is "NEMA Design N". From my own research, including the minimal info they sent me after asking them what the difference was, these specs appear to be wrong. "NEMA Design" letters only go A thru E.
There are some NEMA "locked-rotor kVA/HP" code letters that run A thru V. I suspect that's what these specs are showing, not the "NEMA Design" code letter.
Best I can determine, the "N" model would likely draw more peak current on startup, just momentarily of course, than the "L" model, but possibly up to 20% more. From what I can tell. Customer/Tech support has not provided me with any good reason to pick one over the other.
At any rate, does anyone have knowledge or good opinion on whether this spec is significant or not?
I'm just going to be running it in my garage on standard 110-volt house current circuit. I think it's a 20-amp breaker.
I guess the bottom line is, is either of these motors more likely to trip my breaker when I switch it on, or run less efficiently, or burn out sooner?


(I DO have a 220 outlet in the garage, but I'm already running my air compressor on it. I guess I could run 2 machines off it if I had to... I just don't know if that would be the better way to go or not.)


I will gladly accept redirection to any other threads that you might know of that already discuss this type of info in some depth.


And, do you think this is a "good deal"? Any better suggestions would be appreciated. ;)


Thanks!
 
In this case, the only designators you need to be concerned with are the Enclosure type (TEFC) and the frame size, which is 56C. TEFC (Totally Enclosed, Fan Cooled) means metal dust can't get into the motor and short it out, and there is a fan mounted to the motor shaft.

The frame size is what determines the mounting hole pattern, shaft size, etc. If you build your grinder with a 56C frame motor setup, whenever you upgrade to a VFD and get a 3 phase motor, all you have to do is buy one that is a 56C frame and it will drop right in. I'd stick with TEFC as well. (the "56" is the frame size. The "C" part of 56C means the motor can be mounted on the "face" and has an alignment ring on the face and 4 threaded bolt holes for face mounting.) A 56 motor will be the same size frame but can't be mounted by the face, it can only be mounted on the base plate.

The pulley sizes, motor mounts, etc won't change. The overall power draw on the motors is going to be about the same. The 230V model will draw less amps and you can run smaller wire if you wanted to, but honestly it's a wash. (***Having said that, in my experience 220V motors are more robust than 110v motors and I believe run a little smoother under load. No need to get into this unless you really want to. But given a choice, I would choose 220V unless it's just too much of a PITA to run 220VAC.)

If you are running off a 20A breaker, size the wire larger than that. The circuit breaker is there to protect the wire from catching on fire, not to protect the motor. Your wire should always be sized to carry more current than the breaker's current rating.


Either of these motors will work for you. Being that you are going single phase (therefore single speed) I assume you are using step pulleys, because starting out with a motor running 3600 RPM is going to be daunting.
 
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Just another place to look. I got a used motor from an electric motor repair shop in my area. Had to pay tax but no shipping, Ed
 
Personally, I would try to find a lower RPM motor, such as a 1725 rpm. As John mentioned..... the high RPM is tough to deal with. :) In this case I doubt step pulleys are going to be able to slow your belt speeds down enough. If you're just learning, a "fast" grinder can drive you nuts...... and wreck a lot of projects.
 
I agree with Ed and the other folks. "IF" I were to use a 1 ph motor, I would certainly use a 1725 RPM motor. Playing with the pulley ratios and drive wheel diameter you can get a 1,000 SFPM belt speed which is "ok". That's what I did with the first grinder I built. I felt that was just fine speed control with a 3 step pulley setup. The 2nd (and last) grinder I built I went to direct drive with VFD..... WOW!!!! What a difference. For this I did use a 3600 rpm only because of the cost difference. I have 300 SFPM to 4,000 SFPM belt speed. MUCH better. "IF" you are a hobby maker who plans to make 2 or 3 knives/mo, then the route I (and many others) went by using a Chinese VFD for a cost of $120 or so shipped. A 2hp 3 ph motor from the place you linked to is only $126 shipped so you'll save some money there. If you have to buy the bearings, shaft, and pulley for the step pulley setup, you'll find it's actually less expensive to go 3 ph motor/VFD drive from the start.

The Chinese VFD is a NEMA 1 enclosure and will require either a decent filter mounted over air intake, or mounting in a box. If you're interested in this approach take a look at this thread:

http://knifedogs.com/showthread.php?38839-New-Grinder-for-me

Any questions, just holler.

Ken H<

edit: If you plan to use the grinder several hours per day I would STRONGLY recommend a NEMA 4 VFD drive such as a Telco or other VFD. For a few hrs use per week the NEMA 1 enclosure can work just fine with proper care.
 
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Wow. Great info. Exactly what I needed.
Looks like I have some more reading and re-think to do but that's fine. I'd rather do that now, and get this done right, than cry about it later.
Thank y'all very much.

Dave
 
Dave, if there is any way possible to fit a VFD into the budget, you should really try to make that happen. it will pay off huge.

tip: you'll likely end up with a disc grinder in the future. you can make pig tails and run either machine off that one VFD. Not only does that give you variable speed on both machines, but you get away from single phase motors.


Sent from my iPhone using Tapatalk
 
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