Rebuilding a TEFC?

[N Hurst]

I'm working on building a Frankenlathe using an old TEFC motor on a cheapo lathe that I got for free because it had a dead motor.

I was trying to install the new power cord on the motor when one of the posts where the wire connects to the motor snapped off.

I pulled the motor apart to remove the broken post so I could hunt for a replacement when I noticed that all of the internal wiring had cracked or missing insulation. Is this motor a hopeless cause? I can't afford to spend too much money getting the thing running because I'm starting from scratch and I'm still needing tools and books.

So, I'm confident I can get the post replaced and the motor back together and wired up, but is it even possible to replace the internal wiring? At this point in time, my time is not worth more than my money, so I'd much rather do it myself and learn something than take it to a shop.

Thanks!

-Nathan

[Dr. Deb]

Nathan, electricity operates on the prinicple of electrons flowing to a level potential. For any, repeat any, electrical apparatus to work involves some form of a controlled movement of electron flow. When a source of electrical power is connnected through a controlled series of contol devices we get work from it(be it your computer or motor). When there is no control device between a source of excess electrons and a source of a lack of electrons a condition exists called a "short." In such a condition all the electrical potential is discharged immediately.

All that to say, if the windings are in the condition you said they are and you plug it in, life will, not may, get very interesting - if spectacular. Hopefully the circuit breaker will kick out before you get more involved in the show than your beneficaries would have wished.

Bottom line, throw it away, it can kill you.

Deb

[N Hurst]

I reread my post, and I was a little inaccurate with my description. Sorry about that. Late nights do that to me sometimes. :-)

The windings are OK, and the motor worked just fine before I pulled it all apart. The only conductors with issues are the "last leg" wires that are the stranded cables that connect from the windings to the wiring plate where you connect the AC power cord. I wasn't able to get a good look in to the guts of the motor to see where or how those stranded cables connected to the windings, so I was mainly looking for some guidance as to how they're connected and how I can get to them.

As far as I can tell, the windings and housing is in good shape. I just want to see if I can repair the wiring with cracked insulation so I can be safe.

I hope that clears things up a little. Sorry for the confusion!

-Nathan

[Puckdropper]

N Hurst wrote in news: [e-mail]:

When testing suspicious electronics, I like to stay around arm's length of the outlet so I can grab the plug if anything goes wrong. With a bigger item like a motor, I think I'd plug it in to a power strip so I've got a switch a good distance away.

Concrete and metal can withstand fire much better than wood...

15A at 120V is plenty of power to start a fire. (In fact, the lighter on the grill takes a 1.5V battery to do it's thing.)

Puckdropper

[Bahremu]

Nathan, if the windings themselves are damaged, you can send it off to get re-wound. Re-winding a motor is usually cheeper then buying a new motor. On the other hand, if it is only the leads coming off the motor windings to a terminal board or connection box, whatever, you can replace those wires. Use an equivalent guage (copper thickness) and an equivalent rated insulator (the rubber cover of the wire -- a

300V rating is pretty standard in 120V motors). Solder the new wire to where you cut the old one away and cover the joint in heat- shrinkable tubing.

If you can't do this yourself, find a friend who will or take it to a motor repair shop.

[Lew Hodgett]

Couple of questions.

If you have life insurance, are the premiums paid?

Have you named a beneficiary?

For any motor 10HP or less, don't waste time or money having it rewound, new replacement will cost less.

Lew

[N Hurst]

Yep, yep, and yep.

The windings are sound, it's just the leads that need attention. The motor worked perfectly fine when I tested it, but the leads are needing attention, that's it. If I can get that post and the leads replaced, the motor should be back up to usable condition.

If I'm forced to put much money into it, I'll be forced to just shelve the whole idea until I can salvage another motor from somewhere else.

My main problem is getting to where the leads connect to the windings. I can't really tell how the windings are mounted inside the chassis of the motor, and didn't want to go digging at random trying to figure it out.

Thanks for all the responses. I do appreciate it. I know more now than when I started (mainly missing terminology, which has caused some confusion), so that's something.

-Nathan

PS Lew, I don't think I'd even know what to do with a 10hp motor if I came across one! The biggest I even have any experience is this 3/4 one and maybe the one in my table saw. I don't know any of the specs on that one.

[Lew Hodgett]

motor worked perfectly fine when I tested it, but the leads are needing attention, that's it. If I can get that post and the leads replaced, the motor should be back up to usable condition.

Usual method is to remove end bell to gain access.

Removing the end bell usually brinnells the bearings requiring replacement.

It becomes a loser no matter how you look at it.

Lew

[Robatoy]

EEluktrisities are my bag. That is why I seldom, if ever, offer advice... unless we're cruising for a bruising, at which stage I jump in and shout: "DON'T!!"

Buy another motor. Shop around. 3/4 HP ball bearing motors are all over the Net and cheap.

r

[Stuart]

My daughter, a blacksmith, found a similar problem with a 3hp motor on a second-hand power hammer she bought. I looked at it but decided it was best taken to a motor re-wind company who did the repair for quite a bit less than we expected.

Of course they also do proper electrical tests before letting us have it back so we have peace of mind about it.

[N Hurst]

Thanks for the guidance and advice. I was able to take some good time tonight to focus on the motor housing and get the cobwebs and grit blown out to see what was what. I can see that this is pretty much out of my capabilities without some assistance from someone who knows what they're doing.

I went by a motor shop this afternoon and they quoted me a price of ~ $200 for a new Baldor motor. And that ain't gonna happen when I can get an entire lathe from Rockler for $250. The guy I spoke with gave me a company name to call tomorrow, but he agreed that usually a 3/4 hp motor gets tossed when it stops performing.

He helpfully mentioned that copper prices were up, though, in case I wanted to scrap the motor. :-)

Who knows, maybe someone will consider trading me a motor for the

100:1 gear reducer and motor gizmo I've got sitting around...

Thanks again! From a guy who likes to avoid getting zapped about as much as he likes avoiding spinning metal blades;

-Nathan

[whit3rd]

The insulation you refer to is probably 'spaghetti' sleeving, not the enamel coating of the internal wiring. Sometimes rubber-insulated wiring is crimped to the enamel magnet wire, that rubber used to be susceptible to embrittlement with age (but that doesn't explain the post coming loose).

Spaghetti sleeving is replacable, of course, but it got brittle and cracked, and the post broke free, because of some long overheating (or chemical attack?). I'd suspect the permanent lube in the bearings, too.

I'd go ahead and wire it and use it, BUT two possibilities are disturbing: (1) there's supposedly a thermal overload device in there, why didn't it trip? (2) overheating might be the result of shorted windings, i.e. the enamel coating of the internal wiring might be bad.

A motor rebuild service can check those possibilities.

[Anon Ymous]

I've used shrinkable sleeving to repair some damaged insulation where the rest of the wire was intact. Slide it over the wire & use a hair dryer to shrink it down. Two layers provide greater abrasion resistance. Be careful and err on the side of caution.

N Hurst wrote:

[Stuart]

a motor, my feelings would be to use Silicon rubber or woven glass fibre push-on sleeving, as both will withstand high temeratues, muck, dust and grease better than heat-shrink. It doesn't matter if it's a losse fit over the wire as long as it insulates it properly. A blob of "liquid" Silicon rubber at the winding end will help secure it.

(Usual disclaimer)

Stuart