Help me not fry my motor

R

Randy3000

Joined
Jun 3, 2017
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3 phase motor, the "low voltage" is what i will be doing. The motor came with T7+T4, T8+T5, and T9+T6 leads already twisted together in those 3 pairs. So this is for the "high voltage".
JgKYJ6P.jpg

So, what i am trying to wrap my mind around, is i need to twist all 3 leads T4+T5+T6, and put a wire nut over them and stuff them back into the motor box, right? And then twist up the pairs T1+T7, T2+T8, T3+T9 and stick these into my vfd into U V, and W respectively, and if the motor doesnt turn the way i want with vfd in forward mode, i just swap two of them around? Does that sound right to you? Any good tests i can do with a multimeter before giving it power?
 
Randy3000 said:
3 phase motor, the "low voltage" is what i will be doing. The motor came with T7+T4, T8+T5, and T9+T6 leads already twisted together in those 3 pairs. So this is for the "high voltage".

So, what i am trying to wrap my mind around, is i need to twist all 3 leads T4+T5+T6, and put a wire nut over them and stuff them back into the motor box, right? And then twist up the pairs T1+T7, T2+T8, T3+T9 and stick these into my vfd into U V, and W respectively, and if the motor doesnt turn the way i want with vfd in forward mode, i just swap two of them around? Does that sound right to you? Any good tests i can do with a multimeter before giving it power?
Click to expand...

You've got it, nothing to test without power, unless you're concerned there's a problem with the motor (short, faulty ground, or burnt windings, etc), if it's a new good motor, just wire it up and go.


Set the 2X jumper if it's a 1700ish RPM motor, adjust min rpm to your liking, turn on injection braking, and if it shudders like crazy at any rpm, adjust slip comp, bear in mind, you need to test this under load, i.e. with a belt tensioned over the drive wheel connected to a grinder, not just unloaded free spinning spindle.
 
To run that motor on low voltage, lucky you. No matter how badly you hook it up wrong, It wont run properly or run at all. But you cant hurt it provided you dont just leave it switched on like that indefinitely.

Just to be clear. You mention ”just swap two of them around”.
Thats the wires from VFD to the motor. Dont swap anything of the motor itself.

Anyway, as far as diy meter testing.
If thats a used motor. You should at least verify equal resistance of its windings. And verify infinite resistance between windings and between windings and motorframe.

Outside the scope of some guy lashing up a knifegrinder.
Any testing more advanced involves a specialist instrument for insulation breakdown testing.
Essentially is looking for insulation weakness what might indicate motor soon to fail due to abuse or just very old.
 
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Sounds like you have a pretty good handle on things. I wouldn't worry about testing with a meter. Wire it up and hit the go button.

Not sure how close your VFD is going to be to your motor, but instead of wiring the twisted leads directly to your vfd, I'd recommend pig tailing to some 4 wire SO cable, or you can use some stranded single conductors through some seal tight or similar. If you use the SO cable, you can get some cable glands, or just use regular romex clamps and pump a little silicone around the holes.

Also, make sure to ground your motor chassis.
 
You got it and no need to test it with a meter but double check the wire numbering before powering up. I've had helpers confuse 6 and 9 before.:mad:
 
I have already observed the 6 and 9 confusion. Fortunately, T is oriented, so i just have to make sure i am looking at the T right and then the number is correct.

I dont see a ground screw anywhere on the motor. Should i sand off some paint inside the box and thread a ground screw in there?
 
I dont see a ground screw anywhere on the motor. Should i sand off some paint inside the box and thread a ground screw in there
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It should have some kind of designated place for earthing connection... But provided you can make a solid connection somewhere onto the motor housing/frame, that will suffice.
 
Inside the peckerhead there should be a screw that looks like it's doing nothing, just screwed into the motor housing. This screw "should" be green, but might not be. That's the usual ground connection. BUT - anyplace you can bond/fasten/screw the ground wire to the motor housing, base, etc is just fine.
 
Ken H> said:
Inside the peckerhead there should be a screw that looks like it's doing nothing, just screwed into the motor housing. This screw "should" be green, but might not be. That's the usual ground connection. BUT - anyplace you can bond/fasten/screw the ground wire to the motor housing, base, etc is just fine.
Click to expand...

It could also be that there's just an empty threaded hole, especially if it was a used motor. Sometimes guys will crimp a ring connector onto the incoming ground wire, and then when the motor is unwired or replaced, the screw gets removed and tossed aside.

If the motor has a reversible peckerhead, you can also just use one of the screws that secure the peckerhead to the chassis if they're on the inside. If the screws are outside the peckerhead, you can use one of those too, just make a little pigtail and use a wire nut.
 
An old construction term for the box on side of motor holding the motor wiring. Perhaps the correct term might be "wiring enclosure"?
 
For so many years peckerhead was the only thing I ever heard it called, so the phrase sorta
stuck. http://electricalslang.com/Slang/peckerhead

"The wiring box mounted to an electric motor is called a peckerhead for reasons which are presently unknown."

I saw another link: https://www.eng-tips.com/viewthread.cfm?qid=192982
""Pecker Head" is a now commonly accepted term in much of the US for a motor termination box. As I learned long ago, the term was derived from "Picker Head" which was a protrusion off of a drum in old farm machinery which caught the material to be picked, be it an ear of corn, a sunflower head, a cucumber etc., and separated it from it's stalk or vine. Because the termination box on an electric motor looked very similar, it was called (probably) "that there picker head thang on the 'lectric motor"! Interestingly enough, in the South the term "Peckerhead" already meant a dullard and was also apparently derived from "Picker Head", but meaning someone too dumb to do anything on the farm but be a picker. With a Southern twang, "picker" can easilly end up sounding like "pecker"."
 
Can't remember where I first heard the term peckerhead... maybe from my dad or his dad, while wiring up a motor? But it seems to be an industry accepted term, as most of the electricians I've ever worked with either used, or understood the term.

As for the "dullard" reference, around here, "pecker" is also slang for a man's... uh... member, so if somebody calls you a peckerhead, they're essentially called you a dickhead. :D
 
The ground screw ended up being plain as day there inside the box. I was blind the whole time....

I got the cheapo $75 vfd 3hp from fleabay. My 240v outlet is a 3 prong, 2 out of phase lives and a ground. It wired up fine. One live on R, the other live on T. The vfd doesnt appear to need grounding. So i just wired the ground from the power cord straight to the motor. Test ran it just now and am giggling like a schoolgirl.

My new sanding belts arrived today and i was hoping to do some work on it, but the shipment contained the wrong sized belts :mad::mad:

So i guess it will be another week before i can really test it. Then i have some finishing and painting to do. I really just want this project to move along. I basically relandscaped my entire backyard, remodelled my shop, ran 240v outlets, and cut down and planted new trees for the past 2 months. I would like to at some point get back to making knives. But priorities, gotta take care of my house. My wallet needs a break. As do i.
 
Glad you got it up and running!

So I am trying to go the other way with mine. I have a kabc 27d and 2hp motor. It came wired and ready for 110. I originally thought that was what I wanted, but am having trouble with gfic tripping, so i am going to rewire it for 220.

But here's my little secret. I hate electricity. I don't understand it. And I'm scared of it. Scared to the point that all day I've been avoiding my garage so I don't even have to think about it. Finally mustered up some courage and went out and stared at it for a bit and came up with some questions.

I don't know how to post a pic, but my diagram is same as OP. So I need to wire nut T7+T4, T8+T5, T9+T6, and then L1+T1, L2+T2, L3+T3 right? So there's six different wire nuts there right? L1, L2, L3 means the wires from the vfd right? And are they specific to U, V, and W, or just hook em up however and switch if motor runs in reverse? Right now setup has SJ00W - 14AWG wire b/w vfd and motor. Is that enough if it's hooked to 220 or should I switch to 12 gauge? The outlet I will use currently has 50 amp breaker, but will only be used for this grinder. Should I switch to 20 amp breaker?

Thats a lot of questions. Did i mention i dont like electricity?
 
T1+T7 = L1
T2+T8 = L2
T3+T9 = L3

When you twist two of the leads together, that becomes one "wire" that goes into either U, V, or W. It seems to not matter which goes where. You should only have 4 wire coming out of the motor one of which is the ground.

Or4Xyrx.jpg


Notice i have T4+T5+T6 twisted together and taped off, they dont connect to anything else. I used a regular black, white, green power cord to connect the L1, L2 and L3 to U, V, W. I used a standalone wire to connect ground from the peckerhead (lol) to the power cord.

As far as the breaker size and wire size, it really depends what size motor you have.
 
Randy3000 said:
The vfd doesnt appear to need grounding. So i just wired the ground from the power cord straight to the motor.
Click to expand...
Surprised and a sceptic of that.
If thats your VFD in the picture of post #18, there is chassis ground symbol on that VFD terminal strip. Appears to be fourth from the left.
 
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Captain McKrae said:
I have a kabc 27d and 2hp motor. It came wired and ready for 110. I originally thought that was what I wanted, but am having trouble with gfic tripping, so i am going to rewire it for 220
Click to expand...

GFCIs do not like VFDs.

Plug it into a non GFCI outlet and see if that helps.
 
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