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Does anyone know anything about reversible induction motors? Answered

 I have a squirrel cage motor from a tumble drier and don't want to wire it up wrong!  I studied the timer switch and it looks as though there is a main power wire which is on most of the time, and this would periodically disconnect and another wire would briefly be connected instead.  I assume this reverses the direction.  I haven't switched the motor on yet, but if it turns out that it starts in a random direction, is there a way to guarantee it will always go one way?

TIA,
Throbscottle

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lemonie (author)2010-03-29

I have a belief that the third wire is part of a starting circuit, you can read more here for one.
These things are designed to rotate in the one direction though.

L

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throbscottle (author)lemonie2010-04-05

Many thanks for the response.  Both windings are connected to an 8uF capacitor - I think it's just one capacitor between them, but it could be 2 capacitors with a common earth.  The extra winding gets it's power through a 2.5 ohm resistor, so this would provide the required phase shift.  I had assumed it must be a direction changing winding because of it coming from a tumble drier, but having never actually seen it in operation I don't know, so I will go with your belief (so the timer must just have provided a pause in the rotation).  Gives me a much nicer circuit to work with anyway :-D

Cheers,
Throbscottle

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lemonie (author)throbscottle2010-04-05

I see not much need for a tumble-dryer to change direction, but wouldn't except that your machine does. I had an old AC motor years ago, which featured a centrifugal-switch, when it got up to speed the switch cut - out, that was a starter circuit which operated for a second or two.
If you have a reverse need, I'd look to a mechanical reverse rather than an electrical one.

L

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throbscottle (author)lemonie2010-04-10

I just thought they did that - I think I got that idea from the ones you find in laundrettes.  Anyways, I'm glad it's for starting the motor and not making it change direction.

Many thanks,
Throbscottle

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