# Dead AC Motor?



## TheArsonSmith (Aug 7, 2018)

While trying to adjust the level of my lathe in this video:






The motor stopped on me and just started humming.  You can see in the video I pulled it and put it on the bench, replaced the start cap with another dissimilar one (I also ordered an exact replacement and tried with that one to no avail) it did the same thing just a hum and even manually trying to start it it wouldn't turn.

I'm guessing the run coil is burned out but a full disassembly didn't reveal anything burnt or obviously broken.

Before I throw the old motor out is there anything I should double check that may breath life back into this guy?

Thanks,
- TheArsonSmith (Bill)


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## RJSakowski (Aug 7, 2018)

Aside from the motor problem, if you are trying to level your lathe using the two collar method, You don';t want to use the tailstock center.  The bar must be free on the far end.


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## JimDawson (Aug 7, 2018)

Centrifugal switch stuck maybe?


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## TheArsonSmith (Aug 7, 2018)

I kinda thought about that, but I should be able to get it started by hand still right?

While it was apart I also did flip it backand forth by hand a few times and it seemed to move freely.

This was the first time I've ever had an AC motor like this apart past the startup capacitor though so I really didn't know exactly what to look for.


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## RJSakowski (Aug 7, 2018)

I think your assessment of a run winding going south is likely correct. but check the centrifugal switch anyway.  It takes a bit of speed before the run winding is capable of overcoming the load.  
I would check for continuity on the run winding. If there is continuity, most likely a shorted winding. If the winding is open check fo ra bad connection.  With the capacitor removed, do you still get a hum?  If not, another indicator for an open run winding.


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## Ken from ontario (Aug 7, 2018)

deleted


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## BaronJ (Aug 7, 2018)

Hello Bill,

After watching your video about the motor on your lathe !  The fact that the motor hums and the rotor remains stationary, suggests that the start windings are OK.  You really need a multimeter on the ohms range to check the run winding resistance, and see if it has gone open.  Did you check to see if the bearings were OK ?  Because bearing failure can allow the rotor to touch the stator and you will get the noise, the buzz you heard.

Anyway nice new replacement motor.


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## TheArsonSmith (Aug 7, 2018)

I'll pull it aprt and try checking the resistance across the coils when I get home tonight.


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## whitmore (Aug 7, 2018)

TheArsonSmith said:


> The motor stopped on me and just started humming.
> I'm guessing the run coil is burned out but a full disassembly didn't reveal anything burnt or obviously broken.



There may be a thermal cutout wired into the motor, and those are often replaceable.   Otherwise, look at mechanical
connections of the internal wiring (the run wiring goes to a terminal, it could be just a loose nut or bad crimp).


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## BaronJ (Aug 8, 2018)

Hi Guys,

A motor of that size doesn't  usually have a thermal cutout embedded, if they do have one, it is often a resetable one with a red button visible from the outside.  In any case it would cut power to the whole motor, not just the run winding,  so if that were the case there would not be any hum.

I do agree that loose wiring, or bad crimp, even a break in a wire could cause the motor failure in the way it did.  My best guess would be bearing failure since there seems to be no sign of overheating,  particularly because of the difficulty in rotating the motor shaft when power is applied.


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## markba633csi (Aug 8, 2018)

Centrifugal switch jammed up or stuck somehow is my guess- happens after many years sometimes
mark


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## BaronJ (Aug 17, 2018)

Hi Bill,

Did you get any resolution as to the reason the motor failed ?


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## TheArsonSmith (Aug 18, 2018)

I've had some other projects interrupt so the motors been sitting.  Have a Karate thing with my son today but I may see if I can get to it tonight and at least check the resistance across the coils.


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## TheArsonSmith (Aug 19, 2018)

It seems the run coil is shorted out.  I put a millimeter on it last night to see what the resistances were and it was shorted out almost completely.  Not sure why it wasn't popping the breaker right off the bat.


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## BaronJ (Aug 19, 2018)

Hi Bill,

Thank you for your reply.
I'm not sure that you used the right meter setting to measure the winding resistance.  As you rightly say, if the coil was shorted it would pop the breaker.  From your video, it was obvious that it didn't.

You need to use an ohmmeter to measure resistance !
Using the ohms range on your meter, compare the resistances of the windings.  If the motor is still apart you will need to measure between the ends of each of the two stator coils.  Whilst is is apart check the motor bearings. Look for any signs of rubbing on the rotor and inside the stator.

I hope that this leads towards salvaging the old motor.


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## tq60 (Aug 20, 2018)

If it just hums the run winding likely good and not shorted.

Start winding or start capacitor if equipped bad.

Look for switch apparatus at end of motor.

Likely not closing.

Sent from my SAMSUNG-SM-G930A using Tapatalk


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## markba633csi (Aug 20, 2018)

What type/ brand of meter did you use? Most cannot measure very low resistances accurately (5 ohms or so) you would need around a RX1 range to do it with a mid-scale of about 50 ohms or so
mark


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## TheArsonSmith (Sep 6, 2018)

It was a decent brand, not fluke and don't remember right now without heading down to the shop.  Although it is quite old.  It may have been just really low resistance showing shorted.  I did give up on it and the motor went out with the last trash pickup :~(


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## BaronJ (Sep 6, 2018)

Hi Guys,

With the price of copper today, those windings would have ended up in my copper scrap bin.  The last batch I took netted £28. about $36.
Electronic circuit boards are very profitable as well, but you do need a lot.


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## TheArsonSmith (Sep 6, 2018)

completely forgot about that, I do have a copper scrap pile saved for either melting down or recycling.  I was kind of at the point that I really wanted to move on from that and get to the work I needed the motor to do.


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