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Electromagnets: Insulation concern

  1. Mar 15, 2007 #1
    I'm constructing an typical electromagnet, wrapping coil x amount of times around a 1" diameter iron bar, and getting power from 'D' cell batteries. My question is how thick can the wire's insulation & jacket be?

    Most of the examples I've seen used a nail, with 22-26 gauge copper or magnet wire that has a thin coat of enamel insulation. I'm proposing to use a 5mm (4 gauge I suppose) copper core wire, with nylon insulation and a PVC jacket. The total thickness of the wire is about the size of a pen. Would this type of wire generate a magnetic field?

    Thanks.
     
  2. jcsd
  3. Mar 15, 2007 #2

    berkeman

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    Staff: Mentor

    Magnet wire has thin insulation on purpose, so you can stack as many turns as possible in a finite volume. Using wire with thick insulation will limit how effectively you will be able to turn current into magnetic force.

    And why are you using such a thick metal wire? You would only use that for very high current carrying capacity, and you are not going to get anything like that with D-cell batteries providing the power.
     
  4. Mar 15, 2007 #3
    So it's possible with a higher current? I'm looking to get at least two layers in.
     
  5. Mar 15, 2007 #4

    berkeman

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    Staff: Mentor

    To maximize your power transfer, you would want to match the resistive load of the coils to the source power supply. Do you know the output resistance of a D battery cell (and how it varies with discharge)? Almost certainly the best wire for you to use will be 28AWG or less, and preferably smaller and with magnet wire insulation.
     
  6. Dec 10, 2011 #5
    Why is it important to have the copper wire insulated? Does insulation increase it's effectiveness?
     
  7. Dec 10, 2011 #6

    DaveC426913

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    Gold Member

    Because it's running electricity.
     
  8. Dec 10, 2011 #7

    vk6kro

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    Science Advisor

    The wire has to be insulated because, otherwise, the turns of wire could contact the turns of wire next to them.

    So, the electric current would go between the wires and not around the coil.

    The magnetic field is generated when current flows in many turns of wire.

    Short circuiting the turns of wire would result in reduced or no magnetic field.
     
  9. Dec 13, 2011 #8
    You need some insulation but not a lot because electromagnetics operate primarily as "current" devices with very low resistance so the voltage drop between adjacent turns (or even extreme ends) tends to be very small, which means the electric field the insulation must endure is not generally close to the insulator's dielectric strength. This is why a thin layer of enamel (paint) insulation is generally enough for most applications.

    As an example, I've working with an electromagnet that runs 100 amperes and it only uses enamel insulations: the end-to-end resistance is only 0.030 ohms so the total voltage drop is still only 3 volts. Enamel insulation is more than enough.

    As a side note, the wire has square cross-section because it packs the cross-sectional coil area better than round wire. Just a factoid of interest.
     
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