Help with Induction Motor

Discussion in 'General Electronics Chat' started by blah2222, May 5, 2010.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Hi, my question is just on the basis on a small summer project I have. I'm currently in 2nd year and have taken a couple Electricity and Power courses, and am very interested in building my own induction motor.

    My actual question is just how manageable building a single-phase or even a three phase (2-pole) induction motor is?

    I understand that the three phase is better suited for large scale power operations but I have no clue what the feasibility of building these things are, or even how much I might be spending in time and more importantly in money.

    Just curious,

    Thank you for reading,
    JP
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
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    85
    It is fairly easy to build something that will demonstrate the principal.

    Impossible to build an induction motor that will compete with commercial mass-produced one.
     
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  3. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Oh for sure, in no way do I want to build a commercial-equivalent motor lol, mine would be pretty crap lol

    Thank you for the reply.

    Just another quick question. In school, I'm more comfortable with the three phase model. For my supply can I just set up my sources as three outlet AC adapters then space the poles 120 degrees apart? Adapter output voltages to use?

    Ideally I know that the motor speed is determined on the poles and input frequency but is what types of input voltages should I be using?

    Thanks again,
    JP
     
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    What's going to provide the 120 degrees phase shift of your three AC adapters?
    Adapter voltage will be determined by the windings of the motor.
     
  5. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Actually yeah, I don't really know how to get a three phase source...
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    The simplest AC motor is a 'shaded pole' type.

    Put a coil on one end of a mild steel bar and put a copper band around the other.

    Place the middle of the bar near (tangentally to) a metal disc mounted on bearings.
    The disc will rotate.

    With a disc around 3" diameter, the bar could be about 5" long.
    The bar should preferably be laminated, or made of a bundle of soft iron wire. Roughly 1/4" to 3/8" diameter should work.

    The copper band can be made of bare copper wired, a couple of layers making up about 1/4" length on the bar.
     
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  7. JDT

    Well-Known Member

    Feb 12, 2009
    658
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    Many years ago I made a demonstration induction motor. I got some laminated iron strips from an old transformer. I made 4 solenoids by winding wire round these strips. I think each solenoid core was about 3" long by 3/4" square. Wind a 100 - 200 turns of reasonably thick (say 0.5mm dia) enamelled wire on each one. I fixed them to a board in a cross shape. For the rotor I used a bit of copper pipe (about 1.5" in diameter) with an end cap soldered on. I balanced this on a nail so that it could spin. Connect with a series capacitor as shown in the diagram and apply AC volts from an isolating transformer (a big one). Apply a low voltage at first (say 12V) and see what happens. Check that things are not getting hot! Look for a motor start capacitor. Do not use an electrolytic. Value not critical but larger value better.

    There will be a lot of humming and buzzing but the copper tube should spin.
     
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  8. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    So this is the capacitor star induction motor (single phase)? We briefly went over this type, but I was not really 100% on it. So the cap provides roughly a 90 degree phase difference between the current in the auxiliary winding to the main winding. The for some reason a torque builds up because of the difference in phases of current...

    If you don't mind could you quickly explain, I think I have most of it understood,

    Thank you,
    JP
     
  9. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    How many types of motors are there, and how many are actually practical for household utilities, (fans/pottery turntable...)? lol
     
  10. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
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    The shaded pole type is probably the commonest type in low torque applications.
    Portable fan heaters, ceiling fans and older record decks are some example.

    They are quite distinctive as they don't have a capacitor, but have one or two copper bands on the stator. The eddy currents in the shorting bands provide the phase shift to start the motor.

    The common style in small appliances have squirrel cage rotors but that in not needed, a simple metal disc will work used in an electric meter.

    They are not high torque, so they are not used in applications that have a lot of starting load.

    The common motor for higher starting torque applications is the capacitor start type. These are virtually universal in refrigeration compressors.

    A lot of general domestic appliances and hand tools use 'universal' style motors, which have a series field and a wound armature with commutator and brushes.

    Larger power tools like bench saws or air compressors would probably have capacitor run or capacitor start type motors.

    For info, a three phase motor can be run on single phase by adding a run capacitor between the third terminal and one of the AC lines. It won't have as much torque as on true three phase, but it's a useable system in some applications.
     
    Last edited: May 7, 2010
  11. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    I'd say the best way to 'build' a motor, is to take an exsisting one apart, examine it, and put it back together. You may not have the satisfaction of doing it yourself, but when you get older, you'll appreciate the time you had to advance your skills, rather than wrestling with details.
     
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