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Is microwave turntable motor reeally a synchronous motor?

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LAN_403

radiotech

Fri Apr 30 2010, 08:56PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

How do I remagnetize a rotor to have two poles?

If the number of pole pairs is reduced, the speed will increase.

Have you mapped the rotor to see what the magnetization is?

You could use something like this.

cavemen

Sat May 01 2010, 05:35AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

the speed is increased?

then i am totally lost with my logic

There is a coil of wire that surrounds a rotor.
AC needs to create a standing wave in that coil to turn the rotor.
How will the number of poles decrease the rotating speed of the rotor.

If I want to make my motor put out 60 revolutins per second then how frequent my magnitations should be?

I really feel like I will end up using a pair of stepper motors and a microcontroller, which is a whole new field for me to uncover.

I don't have the magnetometer or a gaussmeter but i can beel that the motor creates resistance once every 6 degrees.

radiotech

Sat May 01 2010, 04:48PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

An AC motor creates a revolving field. In your motor, the connection setup of the capacitor determines the direction of rotation. If the motor has one pair of poles, then the field revolves at the same rate as the power frequency.

In an induction motor, if the rotor moved at the same speed as the field, there would no lines of force cutting the conductors, no magnetism in the rotor and no torque. So induction motors have 'slip', and the rotor moves slightly slower, (few percent) than the field.

In a magnetized rotor motor, the magnetism is permanent, and the rotor pole pairs interact with the stator field and torque is developed
at exactly the same speed as the revolving field.

The capacitor is needed to create a polyphase drive, in this case two phase.

The magnetometer is just a compass with a spring return. You can probe rotor with a compass or dipping needle.

In AC motors there is a difference between mechanical and electrical degrees. One pair of poles, has 360 mechanical and electrical degrees. In a four pole motor, there is 360 mechanical degrees and 720 electrical degrees. For every cycle of AC, the rotor turns 360 electrical degrees. So in a four pole motor, that is only one half revolution.

cavemen

Sun May 02 2010, 03:46AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

I understand now.

How can I make my motor run in such way that 180 electrical degrees would equate to 180 mechanical degrees?

I have it carefully pulled apart.

If it will take me to remagnetise the rotor, I am perfectly fine with that, except I am not sure, how to do it. I heared that magnetic wire on a non-ferrous frame can do the trick.

Thank you for your time.

radiotech

Sun May 02 2010, 05:34AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

How can I make my motor run in such way that 180 electrical degrees would equate to 180 mechanical degrees? A two pole motor does that.

I dont know an easy way to make your motor into a two pole machine.

If you can access books: CG Veinott Fractional and Subfractional Motors 3rd. Ed.

cavemen

Sun May 02 2010, 03:01PM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Do you think that if I remagnitize the rotor to have two poles it will run at 60hz withh the AC?

klugesmith

Sun May 02 2010, 10:06PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

cavemen wrote ...
Do you think that if I remagnitize the rotor to have two poles it will run at 60hz withh the AC?

It will run, very poorly, at 600 RPM in the existing stator. YOu should be able to figure out why.

How hard are you planning to work on this?
For a two-pole stator, the laminations and coil from a shaded pole fan motor (such as found in MWO's) might work with your re-magnetized rotor.
Or you could make new sheet metal pole pieces to replace the ones in your motor -
each "washer" will have one pole finger instead of six.

cavemen

Mon May 03 2010, 03:00AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

I would go to plan "B" which is to use a PIC controller and a stepper motor.
THank you for your time though.
You taught me a lot.

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