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Discussion Starter · #1 ·
I picked up a little 1/12 HP single phase AC motor a couple days ago for a project.

In prototyping, it ran fine for 5-10 min under small load with no overheating.

Then I bolted it down to a mount stand. During the process the bottom plate came off. No big deal (I think), put it back on and good to go. I tightened it down to the stand. Upon inspecting it, I noticed more up/down play in the shaft, but didnt think anything of it at the time.

I hooked it up with no load on, bolted to the stand, and it sounded like something was rubbing a little bit. The shaft didn't stay exactly center-line, it would slightly move up and down while turning. Then after about a minute it powered down and the motor casing was really hot to the touch. I let it sit for about 5 min, and when I came back the motor started back up. So I know the thermal protection circuit is turning it off.

But what boggles me is this has no load but now is overheating after about a min of running.

I think I somehow moved a bearing or something else to mis-align the internal shaft so there is some physical resistance inside that is causing this. If this is the cause, how do I re-align it?

Does anyone have any suggestions?

Thanks!
 

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Discussion Starter · #3 · (Edited)
I found out the issue with the shaft play. There was a washer that has a spring characteristic that was missing on the bottom bearing housing. I greased it up and put it back in and now there is no more play.

However, the motor is still overheating at about 1 min of run time with or without a load.

The motor requires a start cap. I am using a recommended start cap of 72-88 uF. I know its working because the motor spins up easily.

Could it be possible that the internal centrifugal switch that cuts off the cap is shorted, causing more heat?
 

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I don't know a lot about motors but I'm pretty sure some motors are designed to have a specific load. If not enough load it will run too fast, if too much load it will force too much.
 

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Discussion Starter · #5 ·
I don't know a lot about motors but I'm pretty sure some motors are designed to have a specific load. If not enough load it will run too fast, if too much load it will force too much.
That is what I was wondering, so I ran it with a load and had the same result.

It also ran fine previously with no load.
 

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Discussion Starter · #6 ·
Could it be possible that the internal centrifugal switch that cuts off the cap is shorted, causing more heat?
Tested and confirmed as the issue!

I started the motor with the cap then disconnected the cap, and the motor ran for over 5 min just fine.

So for some reason the start winding is not being turned off, causing excessive heat in the casing. Now I know what the culprit is!

When the back came off and the shaft came out a little, it must have done something to the switch circuit. What should I look for when looking for the centrifugal switch?
 

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Do you here the switch click as the motor spins up? If not then look for mechanical issue with the centrifugal switch.
 

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Discussion Starter · #8 ·
Do you here the switch click as the motor spins up? If not then look for mechanical issue with the centrifugal switch.
No, I dont actually.

I dont see anything that resembles a switching mechanism inside the casing or on the spinning shaft. However it might be inside the aluminum that is connected to the shaft itself. In that case I will not be able to get in there at all.
 
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