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Correct application of skin effect

  1. Dec 29, 2011 #1
    Hi all,

    I want to resonantly charge a capacitor, i.e. using a coil and diode combination instead of a resistor, in a very short period, which means a high current at high frequency.

    The problem is the coil. I read that at high frequency AC you get to deal with the skin effect, and also the proximity effect, which cause the current to be concentrated in the outer layer of the conductor. This would strongly increase the actual resistance of the coil when compared to DC conditions, and I would need to use large diameter hollow tubing instead of wire to get an acceptable resistance value.

    So I’m not really clear if these effects apply to my coil. On the one hand the current *is* strongly time-variant (a half sine wave); on the other hand it never changes direction: it’s still DC. Does anybody know if skin and proximity effects do or do not apply to pulsed DC?

    Thanks
     
  2. jcsd
  3. Dec 29, 2011 #2
    Why don't you use many smaller size inductor in parallel so you get a lot of surface? But you should be careful, inductor in series with the capacitor make a good series resonance circuit.

    I don't know the detail, but using an inductor for this would not be my first choice.
     
  4. Dec 29, 2011 #3

    jim hardy

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    how big is this gizmo? what kind of frequency?

    welding cable might do
    i find it at my local scrap metal yard for $1.50 a pound. way cheaper than new.

    if it's small
    build one coil with copper tube from hardware store
    and another with wire from hardware store and see if there's a measurable difference?

    if you're using an iron core at significant frequency, losses there will outweigh your skin effect.
    and yes, halfwave rectified has large AC components.

    old saying - one experiment is worth a thousand expert opinions.
     
  5. Dec 29, 2011 #4
    You have a coil and capacitor, so it is easy to calculate the resonant frequency.
    Fr=1/2pi(LC)^1/2
    Assuming that a copper conductor is used.
    d=2.6/f^1/2
    d=skin depth in inches
    f= frequency in hertz
    Unless the skin depth is much less than the diameter of the conductor, there should not be any problem.
     
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