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Need help from elec motor gurus.
By troy, Section Homebrewed Electricity Posted on Mon Sep 29th, 2003 at 01:38:05 PM MST
having trouble with my lathe...

OK gentlemen,
I would really appreciate some help diagnosing my problem, and you guys are the smartest bunch of electric motor people I know. I have a lathe/mill combination machine. A year ago, the lathe got so that it wouldn't start on it's own, I have to spin it by hand and then throw the switch. Then it runs fine. It has a TEFC 3/4 hp 120V 1650 rpm motor with two caps. I sort of assumed it had a start cap and a run cap.
I thought it was a simple case of a bad start cap. So I took the two caps off and ran down to the elec motor place. The smaller cap was a dead short and the larger cap tested ok but weak. I bought two new ones and slapped them on and it acts exactly the same. Grrrrrr.
Before I tear it open and make a mess, what should I be looking for? Just to make life interesting, I had the machine in storage for 8 years, and I THINK I hooked the motor up correctly again, but I'm not 100% certain of that.
Perhaps two photos will help. The first photo is of the wiring block on the lathe motor:

The second photo is of the wiring block on the milling machine motor, which is identical and works perfectly:

In both cases, the large 4 conductor cable on the left comes from the switch, and allows for forward or reverse operation. The two binding posts at the extreme right of the wiring block connect to the smaller of the two caps, and on the bottom row, the rightmost two posts connect to the second cap, so they share the lower right hand terminal. The motor guy said neither cap cares about polarity, so that shouldn't be an issue. I can give you the specs for the caps tomorrow, but I think you can make that out on the second photo with the motor ID plate.
Do I have a bad start winding and how would I check that?
Thanks in advance,
troy
Fixed the images. Not sure why but it had "EM" tags inside the image urls.
TomW

Need help from elec motor gurus. | 3 comments (3 topical, 0 editorial)

Re: Need help from elec motor gurus. (none / 0) (#1)
by JB on Mon Sep 29th, 2003 at 03:41:54 PM MST
(User Info)

I might be wrong or right here Troy but the top photo looks like the green if it is the ground is hooked up to a switch leg. The green going to the red doesnt look right to me in other words. Ive puta few reversing switches in and messed up and fried the contacts. JB

Re: Need help from elec motor gurus. (none / 0) (#2)
by zubbly on Mon Sep 29th, 2003 at 06:19:24 PM MST
(User Info) www.zubbly.com

hello Troy. assuming that your motor worked fine before, you have these possibilities. you replaced your start capacitor and it didn't help, but the old one was shorted. your internal start switch may have the contacts welded together which will blow your start capacitor and possibly burn the start winding. look at the windings, and the one closest to the rotor is the start winding. if it looks burnt and smells burnt, it probably is. the other possibility is that your centrifugal mechanism that presses against your start switch may be rusted to the shaft and is not snapping back at approx. 75% of running speed. if it does not come back and open your start switch upon motor starting, you will burn the start winding in ten seconds or less. open up the motor and get back to us with your observations.

good luck---zubbly

Re: Need help from elec motor gurus. (none / 0) (#3)
by troy on Mon Sep 29th, 2003 at 09:25:48 PM MST
(User Info)

Thanks Zubbly,

I will have to wait until I get the next big turning project out of the way. I happen to be a deacon at church, and we need a new set of collection plates (16). I almost fell off my chair when I priced new ones. $40 ea for fake brass, 100 bucks a shot for real brass or wood. So my wife and I are going to make nice velvet bags with laminated cherry/maple handles for less than five bucks each. It's amazing what you can do with "free" labor. Should have time to open it in two weeks or so...

Thanks 10^6

troy

[ Parent ]

Need help from elec motor gurus. | 3 comments (3 topical, 0 editorial)

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