AC Motor 115volt help please

[sniperam]

Hello everyone,

I bought for ebay a electric motor 115volt 1hp single-phase 1625rpm. It has 2 capacitors. When I plug the motor to the 115v the motor hums and the shaft do not turn. One more thing when the motor is connected to the 115V it is imposible to turn the shaft manually and when the motor is not connected to the 115V I could turn the shaft manually.
What I should do???
Please see in attachement the url for the picture of that motor
Thanks

 

[ScottI2R]

Check starter caps are not bad. Had this same thing happen to my home ac unit.

Scott

I really am a good egg, I'm just a little scrambled!

 

[waross]

You may have bad bearings and the rotor is magnetically stuck to the stator when the motor is energized. There may be iron dust or other magnetic dust between the rotor and the stator.
By now the starting winding may be burnt out. Bad caps or a faulty start switch or relay won't generally lock the rotor. That is either contact between the rotor and stator or magnetic dust. Grinder motors are particularly susceptible to magnetic lockup when someone cleans up with an air hose and blows grindings into the motor. An ODP is a good candidate.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottI2R]

Good point Bill,
My bad, I neglected to consider the "locked rotor" condition before replying. Thank you for pointing this out to me.

Cheers,
Scott

I really am a good egg, I'm just a little scrambled!

 

[waross]

I used to get magnetic dust "lock up" when the saw doctors used an air hose to clean the automatic saw grinding machines.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sniperam]

Hello

Thanks for your help. I don't think that I have a bad bearing because I'm able to spin the shaft with my hand. The issue is only when I plug the motor to the electricity, the motor hums and the shaft did not turn even if I tried to turn it with my hand. It seems to me that the magnetic field lock the rotor. I open the motor and clean the rotor, but I have the same issue. May someone explain to me why there are two capacitors 65uf 240v 50-60hz, normally one capacitor for the start the second one is for what? One more thing I am in Canada we have 120volt 60hz ac.

Thanks for your help.

 

[jraef]

This is not a DIY forum so most likely your thread will be deleted. But you may see this first.

There are several types of 1 phase motor designs out there, you most likely have what is called a Capacitor Start-Capacitor Run version (two caps). It has a centrifugal switch inside of it that allows the starting cap to be in the circuit to get the motor spinning, then the running caps keeps it spinning. If the switch failed to re-close after it last was used, the motor will not start and you get the condition you have observed. Either take it to a motor shop to have the switch repaired or you can try to do it yourself, but you will have to find the parts, which may be difficult for the average person.

Google is your friend. Good luck.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[ccjersey]

this kind of question is welcome at forums like this one

http://www.smokstak.com/forum/forumdisplay.php?f=6

 

[electricpete]

Jeff - note it's not the typical single phase motor fails to start... the twist is the locked up rotor (only when energized) as Bill pointed out. Does that change your response?

I don't understand how metallic shavings might cause this, I'd be interested if there is an explanation.

One thing that occurs to me is the rotor is severely off-center (or loose bearing clearance) and when energized the rotor pulls hard over against the stator. I have a hard time coming up with any other scenario.

=====================================
(2B)+(2B)' ?

 

[Compositepro]

You most likely have worn bearings as Waross said. What you describe is exactly what happens. You will probably be able to wiggle the shaft. Without experience it is difficult to determine whether bearings are worn too much.

 

[electricpete]

That was the same thing I was talking about.... I see now Bill said "bad bearings".... "magneticially stuck to the stator", which tends to clarify it's not just mechanically locked bearings, but excess clearance. But then, when you add in the iron dust or magnetic dust between rotor and stator, that muddies it up for me again. Bill can you please explain what was meant by that?

=====================================
(2B)+(2B)' ?

 

[sniperam]

Just want to said that I open the motor and I saw a relay klixon instead of centrifugal switch. I test my caps and there are good. It could be the relay that locked the rotor?

 

[waross]

The dust, similar to iron filings, is magnetized by the flux and tends to bridge the air gap and hold everything together magnetically.
The motors I suffered were three phase motors and they would lock up and turn at a fraction of an RPM whenever they got steel dust inside.

sniperam: Inspect the rotor and the stator for signs of rubbing or contact.
Try spinning the motor and then energizing it while it is spinning.
Check the bearings for play, especially upwards. Wipe rotor and the inside of the stator with a soft cloth and look for any iron dust on the cloth.
Read fast.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sniperam]

Yeah waross you are truth. There are signs of rubbing on the stator and rotor. At a certain angle of rotation I can feel that the rotor is rubbing the stator. That mean the motor is scrap.
Thank for your help

 

[Compositepro]

Another possibility is that the motor was dropped at some time so the rotor is not centered any more. A centered rotor is an unstable equilibrium and magnetic forces will pull the rotor to one side unless restrained. That is why it will rotate freely until energized. Magnetic particles will also create this problem.