Anyone know electric motors?????

Fuddy1952 · Apr 16, 2022

We removed the cupola fan in horse stable. It has a 3ft square wood mounting frame fan is attached to so we made a 36.25" square box out of 2"×10" lumber.
When first installed we tested it with extension cord, black & white wires poked into plug. It worked perfectly, running over an hour, even cycled on & off.
Then I ran 12-2 wire in plastic conduit up to it, tried, it never ran & tiny whiff of smoke.
I re-tried extension cord test, motor never ran. Blade spins free. Fan mounted in wood so no metal anywhere close.
So fan removed. I removed GE motor. Here is what I measured:
Starting cap 7.5ufd, measures 7.45ufd
Black to white 4.6 ohms
Black to green 1.9 ohms
White to green 6.5 ohms
Starting capacitor leads 87.9 ohms
As you see in pictures, with motor apart there are three windings...heavy copper, a small gauge copper and small gauge dark green. They wrapped string around, string burned in two places I'm pointing to.
Just for fun I put motor together, jumped it two wires black & white and (drum roll)...it ran!!!???!!!
Now I'm completely baffled, it makes absolutely no sense. I know basically nothing about electric motors, but the green (ground) wire measuring like it does to neutral or hot I don't understand. I thought that was ground for metal motor case?
Any assistance, thanks in advance...

Ken45101 · Apr 16, 2022

it has a short to ground. When you tested it (white and black) there was no ground so no problem. However, it was dangerous, you could have been hurt f you touched it and ground at the same time.

When you wired it properly, you heavy current to ground.

It is defective, don't use it.

Ken

Fuddy1952 · Apr 16, 2022

Ken45101 said:
it has a short to ground. When you tested it (white and black) there was no ground so no problem. However, it was dangerous, you could have been hurt f you touched it and ground at the same time.

When you wired it properly, you heavy current to ground.

It is defective, don't use it.

Ken

Wow...thanks! I thought ground green wire to hot or neutral low resistance sounded weird.
It's 24ft in air so nothing will touch it but I won't use it. Thanks so much. I'll take measurements...hopefully I can find a motor & trash can this one.

Ken45101 · Apr 16, 2022

Green (or bare wire in the Romex cable) is ground for the outside cover, the motor frame etc. On a 110v device, black is hot (+110) and white is neutral (the return circuit for the black 110.)

A DC ohm meter will not give you an accurate measurement of the AC impedance because you are measuring a coil and it provides more than just DC resistance.

You said you were using 12-2 wire. I assume that is 12-2 with ground.

Fuddy1952 · Apr 16, 2022

Ken45101 said:
Green (or bare wire in the Romex cable) is ground for the outside cover, the motor frame etc. On a 110v device, black is hot (+110) and white is neutral (the return circuit for the black 110.)

A DC ohm meter will not give you an accurate measurement of the AC impedance because you are measuring a coil and it provides more than just DC resistance.

You said you were using 12-2 wire. I assume that is 12-2 with ground.

Yes...3 wire. So should I:
Replace just the motor. I have two, the squirrel cage similar one & I have two industrial pedestal fans which same diameter blade, but 1/2hp bigger motor (2 speed)...they ohm out fine, work well, I'd just use one's motor, it will physically fit.
Or just buy another fan (about $400-$500).
Thanks...(I'm retired, plenty of free time)

Fuddy1952 · Apr 16, 2022

Forgot pictures:

Doughknob · Apr 16, 2022

All that wire in the windings is “coated.” The burned area has this coating compromised. It likely does not touch wire to wire when cold or not vibrating. But when things warm up and/or vibrate then the compromised coating lets copper to copper in the winding touch. Maybe even touch the steel core slightly.

As others said, It’s toast.

jaxs · Apr 16, 2022

There shouldn't be continuity between green and either wire (much less both) tells you windings are shorted to ground. Not dead zero resistance short but shorted non the less.

ponytug · Apr 17, 2022

Sorry that it burned up. As @Ken45101 put it so well, it is toast. I doubt that it was anything that you did; it just wasn't made properly.

You might just look for your motor replacement online, or for something similar. E.g. Surpluscenter.com;

Electrical - AC Single Phase Motors - Fan & Air Conditioner Motors - Surplus Center

www.surpluscenter.com

All the best,

Peter

jigs_n_fixtures · Apr 17, 2022

You can probably fit either of the motors you have. They are both 48 frames. Does the old motor have a name plate?

oosik · Apr 17, 2022

My Pan Abode cedar home has cathedral ceilings. I have a big 'ol paddle fan in the living room. Up there - real high. It was a Hunter. Smoked itself about fifteen years ago - after twenty five years of use. Must have been something similar to what Fuddy ran into.

ponytug · Apr 17, 2022

Motor wire is lightly varnished and then wound into coils that are placed in the motor stator and tied together to keep them from vibrating. In a good motor, the whole stator is then dunked in an insulating varnish and baked for added insulation and glue to keep the wires from vibrating and wearing out the insulation. There are some great YouTube videos, if you are curious. High efficiency motors can even have square cross-sectional wire for better winding density.

All it takes is a small pair of nicks in the varnish and you have a short in the coils, and all the magic smoke comes out. Given how thin the film of insulation is on a motor coil, it is amazing to me that the shorting of coils doesn't happen more often. A drop of water can really make things go down the tube in a hurry.

All the best,

Peter

Fuddy1952 · Apr 17, 2022

jigs_n_fixtures said:
You can probably fit either of the motors you have. They are both 48 frames. Does the old motor have a name plate?

I pictured original motor name plate & more here.
I have a Hunter fan in garage that I removed from my Grandfather's doctors office. He bought it used in the 1930s, I remember him saying it came from an old department store. Blades reverse by a mechanical lever you push. It's unbelievably heavy...all I could do to hang it. It still works well.

ponytug · Apr 17, 2022

That helps. You have what appears to be a half HP, two speed 800rpm motor. (Not clear to me what the other speed is, but probably 1740rpm.)

On the web, I see lots of folks having trouble cross referencing the GE part number 5KCP39KGN301APM, probably because GE quit making fractional HP motors. So, that means you will be looking for a non GE motor.
So, that raises a few questions;
How long is the shaft, what is the shaft diameter, and does it have a flat or a key way for your fan? How is your motor mounted?

Once you have that, I would suggest calling a couple of local motor supply houses and seeing what they have.

I am sorry, but I am beginning to suspect that the easy way out is a whole new fan. Having just replaced a furnace fan motor, my experience was that getting a replacement fan motor from someone other than the manufacturer can be an extended, not to say painful, process.

All the best,

Peter

CobyRupert · Apr 17, 2022

#1)The windings (black to white) have a resistance of 4.6 ohms.
#2)The fan’s frame (and a little green wiring and whatever part of the winding that’s between the black lead and the short) has a (black to green) resistance of 1.9 ohms.
#3) The frame and the winding add up to 6.5 ohms both mathematically and by measurement of white to green. I believe this tells us the winding between the black lead and the short location adds no measured resistance in measurement #2. I believe this says that the winding is shorted very close to the black lead.