Lenco Motor Capacitor

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A picture on the Turntable Speed Stability Thread of a Lenco motor has a capacitor fitted across the mains switch (see here ). It is claimed that it is a 'AC motor phase shift capacitor'. I believe that this capacitor is fitted by the manufacturer to suppress any sparking when switching on/off the TT.

So what does the 'tuning' of the capacitor achieve? I assumed from the photo that you are reducing the motor noise by optimizing the reduction of AC noise but as my knowledge of motors is limited am I missing something?

I posted the question on the Lenco site, see here.

Lenco Motor.jpg
 
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PRR

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The Lenco is a "shaded pole" motor.

AC motors on 1-phase power "won't start"; same as a 1-leg bicyclist has a hard time starting, or a 1-cylinder steam engine can get to a non-start position. BIG motors all want real 2- (or 3-)phase power so they start full power.

The "cap run" motors in the other thread are 2-phase motors, run on 1-phase power by using a capacitor to phase-shift and give quasi-2-phase power.

The Lenco uses "shading rings" on the magnetic poles, which "split" each pole to provide a phase shift and give quasi-2-phase power. Look at the picture top of this thread. The slender copper rings that cover almost half the face of each coil retard(?) the flux in part of the pole, giving rotary flux action instead of just back-and-forth.

"Tuning" would be up to the motor designer. But I suspect due to the large mass of the Lenco (and the way shaded-pole works), it is not as critical as on smaller simpler motors.
 

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I am the one who posted the picture in the linked thread and the one who had the wrong understanding on the issue.

I have to thank Karl and all the good people here for starting this thread which gives the correct use of the capacitor on this motor.
Misconceptions and/or wrong opinions on technical matters have to be exposed for the benefit of the public.

George
 

PRR

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There's more information on Shaded Pole motors on Wikipedia.
Shaded-pole motor - Wikipedia
Shaded-pole synchronous motor - Wikipedia
Pictures of flux shift (under "shaded pole"):
Principle of Operation - Johnson Electric
Calculations(!):
GENERAL PROCEDURES FOR CALCULATING PERFORMANCE OF SHADED-POLE MOTORS (Electric Motors)
Motors And Drives

I do not know if the Lenco is synchronous or not. Considering it is a very light load and a not-small motor, and has a speed control, it may run as a lightly loaded induction motor at 1,700~RPM or it may run as a full synchronous at 1,800.00RPM.
 
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