AO Smith motor rebuild

[jsburger]

How do I test for that?

On the A O Smith 1/2 HP motors on my 10ERs you can hear the start switch spring loaded mechanical mechanism actuate on start up to open the contact and then actuate again when the motor slows down when turned off to close the contact.

Not sure if that will work for your motor. It probably should be running with no belts to hear it. If you can hear the mechanism actuating then maybe the contact is fused. You will have to disassemble the motor to check.

In the first picture you can see the spring loaded centrifugal mechanism on the left end of the rotor. In the second picture you can see the start winding contact at the far end of the stator.

[richardrouse]

thanks!

One of the wires I repaired was laying accross the armature on the starter switch, holding the circuit closed. I've fixed that problem, but am still not having any luck. the motor will just hum, and then kick out the breaker.

I'm guessing it's still the starter switch, I just need to open it back up and take a look again.

[jsburger]

thanks!

One of the wires I repaired was laying accross the armature on the starter switch, holding the circuit closed. I've fixed that problem, but am still not having any luck. the motor will just hum, and then kick out the breaker.

I'm guessing it's still the starter switch, I just need to open it back up and take a look again.

If the motor is humming on start up then the start winding is not engaged. Dirty contact on the start switch or bad capacitor. Bad capacitor is not likely. Check the start switch and clean the contacts.

[richardrouse]

Thanks for the advice! I'm pretty sure its not the capacitor. I stuck my meter on it and it read around 180 micro- farruds, which is what is printed on the sides.

I will take a look at the starter switch. Hopefully, it'll be easy. One of the winding leads that I replaced did lead to the starter.

[wa2crk]

Do you actually have a meter that reads capacitance? Most multimeters do not have that function.
If the meter reads upscale and stays there you may have been getting a false reading due to residual charge on the capacitor. Short the capacitor terminals when it is disconnected to drain the charge and try again. The meter should go upscale and then return to virtual zero when using the high ohms scale. If the reading goes upscale and stays there and does not go down to almost zero then I would suspect a leaky cap.
45 amps is a LOT of current and I would suspect the panel breaker would trip almost immediately.
Bill V

[richardrouse]

I'm right down the road from you wa2crk! I've got a pretty nice amprobe meter that measures capacitance. I'll try it again in the morning with the ohm meter and see what I read.

The motor didn't run for long when it ran.45 Amps is a lot. When I read it, I went to the electrical teacher's classroom ( I teach at a vo-tech school) and borrowed his meter to verify. His is a fluke, and gave me the same reading.

[BuckeyeDennis]

Do you actually have a meter that reads capacitance? Most multimeters do not have that function.
If the meter reads upscale and stays there you may have been getting a false reading due to residual charge on the capacitor. Short the capacitor terminals when it is disconnected to drain the charge and try again. The meter should go upscale and then return to virtual zero when using the high ohms scale. If the reading goes upscale and stays there and does not go down to almost zero then I would suspect a leaky cap.
45 amps is a LOT of current and I would suspect the panel breaker would trip almost immediately.
Bill V

I undoubtedly put a lot of a lot of people to sleep when I posted this thread, and glazed the eyes of almost everyone else. Sorry, guys.

But to summarize, I measured a stall current (aka "locked rotor" current) of 50Arms on my 520, which is just about the same that richardrouse is measuring. At 50A, the garden-variety 20A breaker on the dedicated circuit feeding my Shopsmith has a specified trip time of anywhere between 3.5 and 18 seconds.

[richardrouse]

The culprit

2015-10-14 10.31.43.jpg (92.88 KiB) Viewed 1767 times

Here's the culprit.


I'm not sure what to call this part. I'm guessing its the centrifugal switch?

It wasn't making contact with the motor starter switch. I popped the little nubbins out of the holes and it made contact.

My motor ran fine for a few minutes until I bumped it, which knocked the centrifugal thingy out of line with the starter switch.

I've got to look around, I must be missing dome parts as I'm guessing that the centrifugal switch isn't supposed to simply float on the shaft.

[dusty]

Don't be too certain that it doesn't just float there. When fully assembled, it may be "trapped" in the proper location. I have never been inside of an AO Smith motor so I don't know. Unfortunately, there are few documents that detail the innards of these motors.

[richardrouse]

You are right dusty! It kind of floats there.

It's real finicky about the placement.

I had it running for a while in forward. Then, when I went to reverse it, the motor started bucking on the table.

Now, it just buzzes. I;m guessing that the centerfugal switch isn't tripping the starter armature any more.