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Electromagnet design

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  • Electromagnet design

    I found this pdf today, whilst looking for something else;

    It's an electromagnet for attracting non ferrous metals, copper or aluminium for example.
    Paul Compton

  • #2
    Anything can be attracted or repelled by electromagnetism (even organic material) its only the size and power of the magnet that counts. Organic material takes a very large E/M and some really serious power.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at

    Southwestern Ontario. Canada


    • #3
      I have an original copy of that book someplace around here, it belonged to my wife's grandad. I recall reading it, you power the coils with ac, and it exploits the induced current in the nonferrous part, if I recall correctly. Interesting stuff, really. I work around some darn big and powerful magnets, never had one attract me...


      • #4
        Originally posted by alanganes View Post
        I work around some darn big and powerful magnets, never had one attract me...
        Perhaps you need a breeding pair ?

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


        • #5
          Originally posted by John Stevenson View Post
          Perhaps you need a breeding pair ?
          But then you end up with hundreds of them. They stick together...


          • #6
            While I thought that the phase shifting and shading pole theories made sense, I thought that the stuff on page 26 was somewhat dubious.

            The effect, at low frequency, of placing some copper washers that will support and induced current opposing the current in the main windings will just be to reduce the overall magnetic field, rather than to produce a special separate field which will proceed to attract a nearby washer.

            The nearby washer won't 'know' that there are washers with an opposite current to the main windings. It will just be influenced by the total field.
            Richard - SW London, UK, EU.


            • #7
              Isn't this just talking about eddy currents? Fairly standard stuff, if it is.


              • #8
                Originally posted by adatesman View Post
                Isn't this just talking about eddy currents? Fairly standard stuff, if it is.
                The eddy currents will produce repulsion. He is explaining his method for reversing this and producing attraction by using the eddy currents in two washers. It seems that it is a balancing act between the field produced by the first washer and the original field of the magnet. Enough of the original field must leak through the first washer to set up a field in the second one. But the effect of the eddy current from the first washer must be the one to interact with the field in the second washer. It seems to be contradictory at first glance, but perhaps he has a way to accomplish this. Look at his figure 39 on page 27. The piece of copper being attracted has an OD that is less than the ID of the washers in the coil. This seems to be his "secret". I am not so sure about his depiction of some of the lines of force in this diagram where they appear to form a spoon shape. His figure 45 shows that the area where attraction is exhibited is rather small and close to the pole of the main coil. It does not extend outside of the ID of the washers in the main coil.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there is a penalty for trying!


                • #9
                  I'm not saying it is entirely hoccuspoccus, but usually these kind of things would have a working example, like "this diameter/length and XYZ turns of #that wire"
                  Amount of experience is in direct proportion to the value of broken equipment.