Magnetic Motors

[Penguin45]

This has been puzzling me for ages!

An Askoll drain pump motor is an “asynchronous” motor; ie it will quite happily run in either direction, as reflected in the design of the outlet tube on the pump housing.

But – the big versions – Whirlpool and Brandt dishwasher motors – only run the “right” way – offset outlet tube proves that.

How do they do that?

Thanks,
Chris.

[M1]

Re: Magnetic Motors

Hope this helps !!

AC motors can be operated in either direction, but the standard AC motor rotation is counterclockwise when facing the end opposite the drive shaft. AC motors can be reconnected to reverse the direction of rotation. This is why many manufactures polorise the connector terminals determining the direction !!

[bobokines]

Re: Magnetic Motors

ER! Sorry M1 That’s totally wrong.

An AC motor with only two terminals can NOT be reversed by changing polarity of the terminals.

P45… I think it’s down to the design of the impellor. If you look at the impellor it has a near 270 degree free movement on the shaft. On the big synchronous motor on the whirlpool machines, I noticed that the free movement is much looser in one direction than the other.

would love to know the definite answer to this one myself, so anyone else with any ideas please chip in.

Bob

[Madmac]

Re: Magnetic Motors

Yep, surely its got to be the way the rotor magnets are arranged. not much you can do to change a single phase stator coil.

What a bloody awful motor though, got one to change next week, gonna take it apart cos now you got me interested p45 ! 😉

[Phidom]

Re: Magnetic Motors

By definition, AC does not have polarity, live does not mean the same as positive.

[eastlmark]

Re: Magnetic Motors

pretty sure those big circ pump motors have some kind of circuit board within them with some Diodes on (IIRC) the small drain pumps do not have these so maybe it is something to do with that?

[wilf]

Re: Magnetic Motors

if I remember right synchronous means it runs synchronous to the supply frequency. asynchronous runs slower than supply frequency usually 1-2{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} (this is called the slip) as the rotor emf is induced from the stator

wow its over thirty years that I last had to recall that!!!!!!!!

wilf

[neptune]

Re: Magnetic Motors

The clue could well be in the comment by Bobokines, that in its unenergised state, the rotor will be much easier to turn one way than the other. Remember the tiny synchronous motors used to drive the timer on early Hoover 1100 washing machines. The timer had two motors , on clockwise, and one anticlockwise. These two motors were identical, except for direction oc rotation. The difference was in the tiny plastic ratchet device fitted to the rotor, allowing it to turn one way only. Now bearing in mind that the starting torque on these motors is feeble, it will fail to start in the hard to turn direction, but will start in the opposite direction on the next half cycle. Next time you change one, take the old one apart and see if I am right.

[squadman]

Re: Magnetic Motors

The motor would require to be DC to have a choice of direction and using a timer with inverse cams and a suitable control unit. A perfect example of this design is the early Philips Permag Motors which ran on DC at about 48vdc

[bobokines]

Re: Magnetic Motors

this is a bit too heavy reading tonight after a few glasses of Grouse, but here is the patent submitted by Askoll for a device to control direction on a synchronous permanent magnet motor…

http://gauss.ffii.org/PatentView/EP1351376

Perhaps this in incorporated in the motor somewhere.

Bob

[Author]

Posts