single ph Induction motor question... table fan vs mirror ball motor

[Electric-Light]

When a standard capacitor start motor is energized without a capacitor, it will not start. If you spin the motor a bit by hand and energize, it will go whichever direction you pre-spun it.

Shaded pole motors have a shading coil to initiate the starting torque to turn the motor in design direction.

What about induction motors used in geared motors like mirror balls and microwave turn tables?
They can start up in either direction from dead stop, but its random.
But then,what provides the initial starting torque?

 

[T.M.Haja Sahib]

In induction motors used in geared motors like mirror balls and microwave turn tables also, there would be starting arrangement. I think the random nature of starting direction of such motors is owing to small operating current with relatively large harmonic components in it. If the supply is purely sinusoidal, the random starting direction of motors would not exist.

 

[Jraef]

Some of those are actually "ECM"s, Electronically Commutated Motors, a form of Brushless DC motor, and the turning in either direction is not as random as you think it is. Often there is some sort of microprocessor involved and it may be keeping track of operating time in either direction in order to facilitate more even bearing wear. It looks random to you though. ECMs are built with the complete electronics package housed INSIDE of the motor, so all you see is the AC feed wires to it which makes it appear to be an AC motor from the outside.

 

[Electric-Light]

I figured it out... it looks like turn table motor is an unrestrained synchronous motor. Motors used for clocks and such are restrained mechanically, so it can only spin one way.

 

[Jraef]

I figured it out... it looks like turn table motor is an unrestrained synchronous motor. Motors used for clocks and such are restrained mechanically, so it can only spin one way.

Wow, learned something new today!

Thanks for that. :happyyes: