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Stiff Wire and Tight Toroids

Discussion in 'Electronic Design' started by D from BC, Apr 3, 2007.

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  1. D from BC

    D from BC Guest

    Does my post title seem a little perverted? :)
    I'd like to lower the copper loss in an inductor design.
    So, I'm lowering the wire gauge to reduce the resistance.
    (I never get something for nothing in electronics.. :)
    Aside from running out of room for turns, could the wire be too stiff
    to wind?

    Some core info:
    100 turns
    Across: 1.1cm^2
    OD: 1.6"

    At what gauge does it generally get too difficult to hand wind a
    tightly wound toroid??

    What's the gauge of the fattest wire that can be found in typical
    switchmode power supply magnetics?

    What's the gauge limit on a typical toroid winding machine?
    D from BC
  2. I would wind a chunk of 3 strand wire made of enameled
    strands. This also increases the utilization of the copper
    (AC resistance closer to the DC resistance) by decreasing
    the fraction of the copper that is inside the skin depth.
  3. They don't need twisting, from a magnetic standpoint. It
    just makes the wire easier to handle. Magnetically
    speaking, you could make 3 separate windings that each cover
    a third of the core, and then parallel them, But you had
    better get the turns count right.

    The trick to twisting wires is to spin the individual
    strands and let then rotate around each other. The Boy
    Scouts showed me the tool, made of two pieces of plank and 3
    bent sections of coat hanger wire, that they use to make
    rope, this way, from 3 strands of twine. But I have
    approximated the effect by turning the three strands,
    together, at one end, while letting the other ends rotate,
    individually. But it is hard to keep much of a length from
    tangling with three ends spinning around.
  4. D from BC

    D from BC Guest

    Wow! Particle accelerator???
    I'll need a thin insulator around the stranded wire..
    Seems like one of those PITA items to find.
    D from BC
  5. MassiveProng

    MassiveProng Guest

    Depends on the hole size, and the wire type. Solid mag wire gets
    pretty stiff below 16 Ga. (relatively). Fingers get sore fairly
    quickly if large quantities of finished product is needed, and
    uniformity is retained throughout.
    Depends on the number of turns you need.
    Depends on the turns needed, and the fact that final operating
    temperature must be controlled.
    The hole diameter is what matters for winding. Hand "winding
    machines" use a poke through dolly/caddy. It has to be very narrow if
    more than one layer of windings is required.
  6. I.D. and wire gauge might be of interest as well. If its too small,
    large wire might not fit.
    Use Chinese prison labor.
  7. Joerg

    Joerg Guest

    When them fingers still hurt the next morning despite a good dose of
    aloe vera?

    I have seen up to garden hose diameter. The drums came in via a railroad
    connector line and were unloaded by a huge crane.

    Don't know the machine limits versus core diameter but why don't you use
    stranded wire?
  8. D from BC

    D from BC Guest

    Would those wires need twisting?

    I'm not sure but I think twisted wire occupies more cross section area
    than untwisted.
    How about no twisting?
    D from BC
  9. Joerg

    Joerg Guest

    Nope. IIRC it was for locomotives for a Brazilian railroad.

    Thin but lots of breakdown voltage? Check this company out:

    A client uses their litz wire and I had to make some experimental pulse
    transformers with it. Very smooth. No cracked nails and not a single
    callus at the end of the week.
  10. Paul Probert

    Paul Probert Guest

    Look into Litz wire. Individually insulated strands braided together.
    Gives you the lowest resistance at high frequency.

    Paul Probert
    University of Wisconsin
  11. Joerg

    Joerg Guest

    If it's not RF then you don't need twisting. Even for a big switcher
    doing a few hundred kHz you might get away without.
  12. D from BC

    D from BC Guest

    On Mon, 02 Apr 2007 17:41:39 -0700, MassiveProng

    Yup... Sounds good..I'll go for that... 16AWG @1.29mm..
    (My rough guess was 15AWG.)
    Any further DC conductivity required and I'll switch to multiconductor
    for easy winding.
    D from BC
  13. Barry Lennox

    Barry Lennox Guest

    My personal limit is around 16g, and I'm not even sure I'd want to
    wind 100 turns with that. A 1-off might be OK, but not 10 !!
    They can go a lot thicker, but Litz wire is more normal.

  14. John E.

    John E. Guest

    Wow! Particle accelerator???

    Would that make it a SMPA? (c:
  15. D from BC

    D from BC Guest

    The ID is 0.95"...A very rough calculation: (pie*[(0.95"/2)]^2)/100 ~
    = 0.007sq in...taken as squares.. root 0.007 = 0.08"...So something
    bigger (thinner) than #12 wire will fill the ID...
    I'm guessing a more accurate calc would yield #15. Still probably too
    painful to wind a tight 100 turn toroid by hand..
    Wow...that's cheaper than those chinese sweat shop kids.
    More crime for cheaper inductors!! :p
    D from BC
  16. D from BC

    D from BC Guest

    Cool ...thin insulation...
    I couldn't find the Litz wire on the site..
    Nor did I see:
    "To order trainload of Litz here.."
    I'll poke at the site again later...

    By the way...I mentioned a thin insulator covering the stranded wire
    (bare stranded wire,not Litzy) to take up less space. I was comparing
    to plastic coated stranded hook up wire.

    My app has negligible losses due to skin effect. Mostly core and
    copper loss.
    Kinda ironic to use Litz wire to control copper loss due to low guage
    wire being too stiff..
    D from BC
  17. D from BC

    D from BC Guest

    There's something you won't see on Ebay...
    D from BC
  18. John  Larkin

    John Larkin Guest

    I knew a guy who wound solid #8 on toroids. He built a machine with a
    flat steel-plate table with a hole in the middle. There was a sort of
    huge crochet hook that came through the hole from below, through the
    toroid, and hooked the wire. Then the operator hit a foot pedal and a
    pneumatic cylinder pulled the hook down, doing the tough part of the
    winding. The rest of each turn was pretty much manual labor.

  19. D from BC

    D from BC Guest

    I'll be staying away from 16AWG or lower..
    I imagined a nightmare project like winding a coat hanger on a toroid
    But that's steel and harder to bend than copper, IIRC from the last
    time I locked my keys in the car...
    D from BC
  20. Robert Baer

    Robert Baer Guest

    Better yet, "pseudo-litz" by using a number of small (insulated)
    wires in a bundle.
    That way, less space gets wasted during winding due to the smaller
    size as well as thinner insulation (use "enamel" instead of plastic).
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