Would this be a good motor for my grinder build?

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Perrin

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May 12, 2013
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I have been researching and shopping for an appropriate motor for my grinder build. It is a 2x72 KMG clone that will use 3 step pulleys (from Beaumont) and a 4" drive wheel. It will use single phase 110v power, regular outlet. I think I have found an appropriate motor at a decent price. I am hoping some of the members versed in electric motor could take a look at the specs and verify if it is what I would want.

2.5 HP, 1800 RPM, 115/230 Volts, TEFC, 56HC, Footed
Item#: 00258ES1R56HC

HP : 2.5
RPM : 1800
Enclosure : TEFC
Frame : 56HC
Frame Remarks : Footed
Volts : 115/230
Phase : 1
Manufacturer : Weg
Condition : New Surplus
Weight: 65 lbs
Our Price:
$167.00

Most of the 2hp I have been looking at are closer to $230. Thanks in advance for any advice given.
 
Perrin, I am no electrician but you cannot use a VFD (variable frequency drive) controller and have variable speed with a single phase motor. You CAN use step pulleys and a jackshaft to run a grinder however. My personal opinion is that once you use a variable speed drive you will never go back to moving from one pulley to another for different speeds. You should look for a 2 hp 3 phase TEFC motor with 56 c face mount AND a foot mount. You can use that motor for a bunch of different grinder designs and will be able to control the speed by twisting a knob. Also you do not need 2.5 HP and 65 lbs is really heavy for a grinder motor. My 2 Hp motor weighs 31 lbs. (1725 rpm). Shop some more for a 3 phase motor and go variable speed! The Kbac 27 d drive can be had for about $350. Buy once and cry once is a wise saying. If you are serious about making knives you would upgrade to variable speed anyway so why spend the money to build an "almost great" grinder?
 
Any idea on the motor's shaft size? That will be important based on the step pulleys you are going to get.

Other than that, it seems like a usable motor for a decent price.

A VFD would very obviously be a nice upgrade, but $167 is a far cry from $350, and you've still got to find a 3 phasea motor and pay for sheaves, bearings, shafts, etc... if going for a KMG clone.
 
A motor that size is going to have a huge current draw at 110v (probably 25-30 amps). Standard 15amp breaker/ wiring won't cut it.
 
LARRYZ10, thanks for the advise but I have debated the vfd vs step pulleys thing already and the step pulleys won out.
Knife to a Gun Fight, shaft size, that's a good question and it's not listed. I need to check, but I think that the pulleys are for a 5/8ths shaft.
Boogaloo, that is also a good question, I will have to inquire when I ask about the shaft size. Furthermore, I will consult my electrician (coincidentally the same person that is my grinder builder) about the electric to the shop.

Thanks, there are a lot of variables to consider in such an endeavor.
 
2.5HP converts to ~1.8kW. So at 115V its gonna draw more than 15.5 Amps. The 2.5HP is power output though, input needs to be 10-20% higher.
So you are somewhere between 17.x and 19.x Amps, roughly calculated. Make sure your wiring can do that ! Or run it at 230V if you can. That way you would only need half the current.
 
Erm, why that ? P=U x I, so I=P/U
1800W/115V =15.6 Ampere
1800W/230V = 7.8 Ampere

Or is there something different in the US that I'm overlooking ? Here its one phase (230V) against neutral
 
Last edited:
My bad, I totally misstated that.
I meant the 1800 watts power drawn would be the same. As you pointed out, a wire will carry half the current in a 230 VAC circuit that a 115VAC circuit wire would carry for the same wattage device.

230 volts is the same everywhere. How it is drawn is not.

In the US and Canada, 230 is drawn from a center tapped transformer. It has two hot legs that will each read 115 to ground/neutral....and 230 volts across them. Each hot leg is 180 degrees out of phase to the other, but when current is drawn across them, it is still called single phase.

In The UK/Europe, 230 is a single phase line voltage reading 230VAC between ground/neutral and one hot wire.

The other difference is that the UC/Canada uses 60 Hz and much of the rest of the world uses 50Hz.

The combination of lower line loss at 115VAC and more power delivered at 60 Hz is why 115VAC is the standard house supply voltage here.

US built motors rated at 115/230V and 60Hz will run a bit slower and develop less power if run on 50Hz. They will also get a good bit hotter.

To explain what my original misstatement was about:
That motor would draw 15.6 amps at 115V and 7.8 at 230V. What many folks don't understand is that in the US, the difference in the wire size and current draw is that what is really happening is that you are drawing 115V at 7.8 amps on two separate wires. This adds up to 230V at 7.8 amps.

It is sort of like filling a swimming pool with a one inch hose. You can only get twice as much water into the pool in a set length of time by either doubling the water pressure, or by using two hoses. If you can only use one hose, the only alternative is to use a larger hose.
 
You had me wondering there for a while ;) I actually looked it up in my textbooks, hoping I didn't miss something embarassing :p

My thinking was that by using a higher voltage, he could get by with smaller diameter wiring. For 20A he might have to re-do the wiring, which can be quite a mess.

Very interesting with the center tapped transformer, didn't know that, thank you. :thumbup:
We only have 230V single phase or 400V three-phase here (shifted 120° from each other)
I always hated calculating the load-balancing in a three-phase net :barf:

Getting way off-topic here, you can move /delete this if you want, but how to you soft-start larger motors ? With a three-phase net you can use wye-delta transformation, how would you do that in two phase-net ? Or do you use three-phase for high-power applications too ?

Sorry, inquiring minds want to know :)
 
J. Hoffman, I believe you are correct.

Also, I should have also qualified my statment that this will be a decent motor if your shop wiring can support it. I would definitely wire it to a dedicated circuit breaker, and if you can swing 230VAC, do so. That said, a 20 to 25 amp CB with 12 gauge wiring would likely be enough to run on 115VAC if wired directly (or with a short cord).

Your electrician friend should be able to get you going fairly easily.
 
C_Becker
Your question is not really OT, as it is part of why just the amperage on the plate isn't enough to figure the wiring requirements.

To soft start a large single phase motor you use a soft starter ( (duh)....AKA a motor starter switch. In 3Ph, they are the norm, but in single phase people often don't realize they may need one. Every VFD has one built in...called "ramp", the single phase versions just ramp the voltage to 100% at a set rate.

It is a device that delivers a lower voltage to the motor to start it and gradually raises it to full voltage. They are usually electronic and the starting delay time can be from a few seconds to half a minute. This allows the motor to slowly build up torque at an even rate. There are old mechanical soft starters that allow a certain amount of "slip" in the motor shaft connection and thus reduce the start-up torque. Delivering too much torque too fast can twist the shaft on the motor or shear gears in a gear box. That is a bad enough problem, but there is an electrical issue also. ( read on)

When a large motor that is in a high torque setup is started, the inrush current may spike at five times the rated current ( or more). Depending on several things, this may only be for a few milliseconds, or for a few seconds. Obviously, if the wiring and/or breaker is barely large enough for the rated draw the motor, several seconds at 500% load would fry something. The reason there are special slow acting breakers for large motors is to allow this initial spike. IMHO, for shop tools of our knifemaking purposes all wiring and devices should be rated at least 125% the standard rating for the motor plate current listed ( 150% if using 3HP+ motors). I would suggest 10 gauge wiring for a 115VAC 2.5HP motor ( 12 gauge for 230VAC, and a 20 amp motor rated "delay" breaker.
 
That is awesome stuff, thank you. Thank you for the direct answers and thank you for the explanation.
 
Thanks for the explanation Stacy. I'm not really familiar with those "big" electrical things. I know a few basics I learned at school, but really more of a electronics guy.

Yes, the initial current spike (up to 10 times was what we learned at school) can really be a problem. Thats why I asked about the wye-delta transformation, because it reduces that initial current to 1/3. But yes, VFD seems the way to go. Interesting stuff for sure :thumbup:

BTW this thread is great for brushing up my technical english :)
 
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