Shopsmith Forums

I pulled open a motor that I am refurbing to find the coils to be fairly blackened.

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Is there a good way to decide if its ok to keep using this motor in its current state? Naturally I will be cleaning out all the sawdust and such, as well as replacing the bearings if its going to go back into service. It is from a greenie, 3/4 hp A.O.Smith. It ran fine before I pulled it apart, except for a little squeeking.

Damagi;
I really don't like the looks of the windings in the motor. If you can , isolate the ends of the run and start windings and check for continuity and then check for any leakage between the run and start windings using an ohmeter. If there is no leakage between the windings that is a good sign. The black windings are what has me very concerned. If the formvar coating on the wires is blistered do not try to use the motor. If it is just blackened try some new bearings and see if the motor runs OK. Bearings are only a couple of bucks. If the formvar has flaked off ANYWHERE on the wires do not use the motor. Clean it and try it. If it bad it will only trip a breaker but you will have two new bearings that you can use if needed on something else.
Bill V

damagi wrote:I pulled open a motor that I am refurbing to find the coils to be fairly blackened.

[ATTACH]12973[/ATTACH]

[ATTACH]12974[/ATTACH]

Is there a good way to decide if its ok to keep using this motor in its current state? Naturally I will be cleaning out all the sawdust and such, as well as replacing the bearings if its going to go back into service. It is from a greenie, 3/4 hp A.O.Smith. It ran fine before I pulled it apart, except for a little squeeking.

Have you measured the winding resistance(end to end and to motor frame and winding to winding)?

I agree it looks very bad.

However there is hope if as you say it was operating correctly prior to disassembly.

The start winding should measure a around 5 ohms(probably less), and the run windings should be a fraction of an ohm. If you have separated the run windings, they should measure the same.

There should be no continuity from any winding to the motor frame(shell).

There should be no continuity from any winding to any other winding, but the internal splices must be opened up to determine that.

Close inspection of the heavily charred wires should not reveal any 'missing' insulating varnish.

I would spray insulating varnish on the windings prior to unsplicing so as to avoid wire movement while doing so.

The nose test is a good indicator here. Obviously it will smell burnt, but the detail is, burnt what(insulating varnish or sawdust).

P.S. The run windings are badly charred, and unless there was little or no air flow or the bearings were nearly frozen(motor was run extensively under speed) or grossly overloaded for extended periods of time there is no explanation for its charred condition.

In ANY event its reliability is questionable, but if it can be useful, it comes with only your time and effort to get that future use. Bearings are not all that expensive, and COULD be reused it it fails early.

I would not sell that motor to someone else however. Tis your risk to be taken here. Also do not use unless properly grounded!!!!!!!

End Sermon!

SDSSmith wrote:I agree regarding resale.

I would ask if you ran the motor before dis-assembly? If so and it ran okay other than bearing noises, I would replace the bearings and use it in a Mini for my own use (until it dies) otherwise part out the rest of the headstock and be done with it.

I was repairing the motor for a guy. After discussing with him, we decided to not move forward with that motor. He is upgrading to an extra 520 that I have extra.

I may mess with this for my own use as you suggest...maybe experimenting with the reversal modifications. Either wya I have a motor to trade in to shopsmith come PowerPro time (if that ever happens for me)

beeg wrote:Run it "AS IS". See which fails first, the motor or the bearings.

Trouble is, dragging bearings aggravate the other 'problem'.

The bearings are simply replaced now that it is 'apart'.

FWIW, it be a good practice run for rewiring(reversing/dual voltage).