Synchronous motor question

[Tim+]

Most small synchronous motors seem to be rated CW/CCW for clockwise & counter-clockwise.

I want one that will run clockwise only. Is it just a question of looking for one that specifically states CW?

Tim

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[Brian Gaff]

If you look in many clocks you often see a little ratchet and spring thing that will kick the motor the right way if it starts in the wrong direction. great fun can be had by disabling this little spring. Brian

[Brian Gaff]

Actually there were motors that used phase to always go the same way, like the old gramophone and tape recorder and very early vcr induction motors. Brian

[The Other Mike]

If it has a four wire connection then a capacitor of maybe 470nF in series with one of the windings can be used to kick it off in the required direction. Otherwise you need mechanical methods such as a spring and a one way clutch

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[Bob Minchin]

Yes clock motors always used to have a mechanical scheme to get them to start or at least change direction if they started off the wrong way. Gramophone motors I've need were always shaded pole type which only went one way due to the shaded pole. More modern small motors such as microwave turntable motors look externally just like the old clock motors but with no visible means of mechanical reversal and always seem to go the same way round - even though in that application it does not matter at all. I've never had one fail and the opportunity to take it apart to investigate. Bob

[DerbyBorn]

Many microwave turnables are random.

[Harry Bloomfield]

Bob Minchin presented the following explanation :

Our microwave is 50/50. It will continue the same way, if restarted not from rest, due to inertia.

[Bob Minchin]

Harry/Derbyborn Thats what I would expect but I'm pretty convinced mine always goes the same way round. I will pay more attention to it when I remember.

Bob

[Andrew Gabriel]

I took apart lots of gramaphones in my youth, and none of them used [shaded pole] synchronous motors. They were all shaded pole squirrel cage motors (non-synchronous, or near synchronous with slip, if you prefer). I suspect the [shaded pole] synchronous motors would not have the starting torque required.

I hate to admit it, but I still have the motors in a box which "might be useful one day", even though not in the last 45 years;-)

As others have said, mine start up in a random direction. I have replaced these at repair events, but not opened one up to see what type of motor is inside.

[Brian Gaff]

Well one shadow pole motor was used in a lot of Akai early tape machines. It was odd as it had the rotor on the outside.

Brian

[PeterC]

I've a mains one that you could have. It's double-ended, so can be run either way. Rotates once per week. Could make an 'interesting' one-handed clock with it.

[Max Demian]

I remember when they played records at the fairground and the pitch varied with the loading on the generator, so they must have been synchronous.

[Vir Campestris]

Mine seems to consistently start in the opposite direction to last time.

Andy

[Andy Burns]

My microwave reverses each time, I presume it depends on a bit of 'spring' left in the gear train?

[tabbypurr]

You have some odd ideas of fun.

[Andrew Gabriel]

Same would happen with a voltage sag on a loaded shaded pole squirrel cage motor.

[Max Demian]

A loaded shaded pole squirrel cage motor? I should have asked the guy on the 'dodgems' if that was what they had. Too late now. Pity.