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Coil winding

Discussion in 'General Electronics Discussion' started by dayanj, Oct 18, 2010.

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  1. dayanj

    dayanj

    15
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    Sep 16, 2010
    I am winding a coil to get a constant magnetic field for my experiments.
    I am using a aluminum bobbin and winding insulated copper coil on it, I need ten layers.
    I was trying to wind it manually but its hard to get neat winding.
    Can someone suggest me any help with this?

    someone said I can use epoxy after each layer to keep that layer fixed, has anyone used it like that? if so which type of epoxy?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    An aluminium bobbin will act as a shorted turn and either shield much of the magnetic field or get really hot and possibly melt (depends if you're using DC or AC).

    If the aluminium bobbin is just there to support the windings while you wind them and you plan on removing it, that is OK. Otherwise, find something non-metallic (and non-conductive) to wind the wire on.
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    As steve says, using AC with a conductive bobbin makes for a dead short, but using DC it won't matter. I'd put varnish inside the bobbin for extra protection for the wire.

    Some people are able to mangle a perfectly straight wire, and some are able to straighten a completely mangled wire. I can't say how & why but it's all in the head & hands.

    Tape is often used to fix layers but if you have more time on your hands then the ethanol based Shellaq or a Polyurethane based varnish are the preferred choices.
    Of course 5-minute epoxy can also be used but it won't stand as much heat as the wire insulation does without softening & melting during use.
     
  4. dayanj

    dayanj

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    Sep 16, 2010
    Thanks a lot for your reply, could you please suggest me any commercial name or how to buy those shellaq or varnish for this specific use?
     
  5. dayanj

    dayanj

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    Sep 16, 2010
    And also can someone help me about how to select a gauge of wire to wind a coil?

    Lets say I want to create a coil to give constant 1T magnetic field.
     
  6. NickS

    NickS

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    Apr 6, 2010
    What calculations did you use to decide the number of windings and the length of windings? The copper wire size should have been part of that. Also what is your power source?
     
  7. dayanj

    dayanj

    15
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    Sep 16, 2010
    well I didn't do the calculations myself, someone else handed me over results, i was thinking whether I can use a thinner wire and change the length or turns accordingly(doing calculations again), since this one im using is hard to wind.
    I am using DC power supply.
     
  8. NickS

    NickS

    367
    0
    Apr 6, 2010
    Check this link out.
    http://www.coilgun.info/theory/magnetwire.htm

    And for the calc you want to use a ferromagnetic core with a known permeability.
    B = (N*I*mu) / L

    B = mag field in tesla's
    N = number of turns
    I = current
    mu = permeability of the core
    L = length
     
  9. dayanj

    dayanj

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    Sep 16, 2010
    Awesome!
    Thanks bunches!!
     
  10. camerart

    camerart

    109
    2
    Aug 18, 2010
    I'm no expert.

    When I wound some pickup coils, I used tubular Ferromagnetic cores. Put a nut and bolt through, then put in a machine chuck. (drill, lathe etc) Then put a gentle tension on the wire as it winds, this helps to be more consistent.

    I think that winding like a basket makes them stronger, and you can let the wire go through Wax to make it stay in position. I actually chose not to do this and use more turns.

    I'm fairly sure that the cross section of the windings is best if it is square. (as wide as it is deep)

    I found it best to wind too many turns, connect up, and while connected carefully unwind turns till the require strength is achieved, then cut and reconnect.

    Hope this helps.
     
  11. dayanj

    dayanj

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    Sep 16, 2010
    It helps a lot!! Thank you!!
     
  12. NickS

    NickS

    367
    0
    Apr 6, 2010
    Minus the wax that sounds good. For an electromagnet you are pumping DC(unlike a speaker) and it will get hot and melt wax. If you do use something to hold the coils it would preferably be thermally conductive and heat resistant.
     
  13. camerart

    camerart

    109
    2
    Aug 18, 2010
    The wax is to hold the coils till they are sealed. Then I use super glue to hold the windings in place, but there is no heat involved.

    I once worked at a motor factory where they soaked the coils in resin and baked them, but the motors were going to be vibrated in use. I presume you will need to search for some sort of glue or resin that can stand the heat expected.

    I think this is mainly needed for consistency of coil strength.
     
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