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AC synchronous motors

 
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Bob_in_OKC



Joined: 16 Oct 2009
Posts: 3

PostPosted: Fri Oct 16, 2009 1:45 am    Post subject: AC synchronous motors Reply with quote

Many stereo turntables - record players - are driven by a small AC synchronous motor. It's a magnet on a spindle, rotating inside a two-piece shell. So my question is simple - Is such a motor supposed to have oil in it?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Oct 16, 2009 2:57 am    Post subject: Reply with quote

There is no need or requirement to have oil inside an electric motor.
If you see any signs, it is from the end bearings that support the shaft.
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Bob_in_OKC



Joined: 16 Oct 2009
Posts: 3

PostPosted: Fri Oct 16, 2009 4:02 am    Post subject: Reply with quote

Thanks very much for the reply. Could you tell me why the motor would develop a grinding noise that starts after around two hours of use? If so...what could be done to repair that?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Sat Oct 17, 2009 5:14 am    Post subject: Reply with quote

Strictly depends on your application and type of motor; In general, the "grinding" noise is normally caused by dried lubricant or worn out bearings &/or bushings supporting the spinning armature on either end of the housing.
If it is a sealed motor, chances of a reliable repair is slim to none. You may be able to buy some time by applying a drop of lubricating oil at the base of the drive shaft, allowing it to work it's way in--it may help. If it is a brush-type, generally it is best to replace rather than repair.
If it can be disassembled, barring from worn out bearings, dismantling and clean and re-lubing shaft/bearings is the way to go.
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Bob_in_OKC



Joined: 16 Oct 2009
Posts: 3

PostPosted: Sat Oct 17, 2009 5:43 am    Post subject: Reply with quote

The motor does open...quite easily, in fact. I can pop it open by twisting a screwdriver in one of the slots on the edge. Inside the two halves is a spinning cylindrical magnet with a spindle that serves as the drive shaft. The bottom of the shaft sits on a ball bearing. The top of the shaft goes out through the top half of the motor and drives the belt. With the idea it's that shaft, I've dropped oil in the bottom, where the ball bearing is. So far so good. Thanks for the help.
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