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Litz wire

Discussion in 'Electronic Design' started by Tim Williams, Feb 19, 2010.

  1. Tim Williams

    Tim Williams Guest

    Not really... I'm going to use 1.00 x 0.040" copper strap on a high amp
    transformer I'm planning. 5V 100A in two turns.

    Tim
     

  2. Yes, low turn counts are possible, and it is good for that, but it is
    not good for any high turns count app. There is square and flat wire,
    but it is far narrower than the media in this thread refers to.

    It is used in speaker coil bobbins too.
     
  3. E

    E Guest

    I have seen that kind of copper foil conductors used in some ATX power
    supplies.
    Don't remember how many turns as I was only interested in the ferrite core
    for
    other projects.

    -ek
     
  4. amdx

    amdx Guest

    The copper rope is not long enough? We've got some discard litz wire,
    Would you care to share info about the physics teaching instrument?
    Mike
     
  5. legg

    legg Guest

    buzz buzz buzz.

    RL
     

  6. Yes, and it would likely buzz as well. One of your legs must have
    fallen off, and this stupidity is your compensation.
     
  7. qrk

    qrk Guest

    What frequency is this for. If you're under 1MHz, you're mainly
    fighting proximity effect, not skin effect. To deal with proximity
    effect, all you need is bunched conductors (twisted), not Litz. The
    Litz wire I have come across use bunched groups twisted into a larger
    bunched group. This closely approximates Litz.
     
  8. Tim Williams

    Tim Williams Guest

    Let's say 200kHz-2MHz.

    Tim
     
  9. amdx

    amdx Guest

    Hey qrk,
    I haven't seen that information before, do you have anything to site
    that would make me believe it?
    To quote Dagmargoodboat, [At 290Khz]
    "Comparing the braid to the equivalent-cross-section solid wire:

    (view table in Courier font)

    Winding Rac (calculated)
    ---------- ------------------
    7 x 0,23mm 1.46*Rdc
    1 x 0,608 4.29*Rdc

    So, the braid was ~ 3x better.

    Here are a couple of skin effect calculators.
    http://daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml
    http://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calculator/

    Ok, you need to explain what you mean by bunched conductors,
    Are they insulated bunched conductors?
    As stated before proximity effect is minimized by making every conductor
    find itself in the same position in the bundle an equal amount of time.
    Twisting may or may not do that, depends on the amount of conductors
    twisted.
    Mike

    Yes, "closely approximates Litz" because it would not be as good
    regarding
    proximity effect. It doesn't have every conductor find itself in the same
    position
    in the bundle an equal amount of time.
    Mike
     

  10. Of course they would be. Use *SOME* common sense.
     
  11. It also depends on what he stated. If the run is short enough it makes
    no difference. Lower frequencies at lower currents also have less issues
    with the outward EM field push that we all know as "skin effect".

    AND the mag field around each individual conductor in a bunch, whether
    Litz woven or not, will be different than that of the solid, so the EM
    field effect claimed to also affect non-woven bundles is not as
    pronounced as you might think.

    The wires in the centers of non woven bundles do NOT exhibit the same
    problem that a solid does. It is several parallel fields, not a single
    conduction field. Yet another reason why the effect is still realized
    sans the weave. It is not 100% efficient, from that perspective, but it
    DOES STILL work.

    It is a fact. Get used to it.
     
  12. amdx

    amdx Guest

    I completely agree Jim.
    I just went on a rant when qrk said,
    " If you're under 1MHz, you're mainly
    fighting proximity effect, not skin effect."
    I don't believe that, and I think a properly sized bundle of twisted
    (insulated wire)
    will have a large effect over a solid wire with the same circular mils.
    (as Dogmargoodboat said, 3x)
    It would be interesting to find what percentage change a twisted litz
    would have
    over a properly braided litz. I'll bet it's under 20%.
    What do you think?
    Mike
     

  13. So.... what a hoot. You accidentally agreed with me?
     
  14. amdx

    amdx Guest

    I'd rather say you agree with me, and in that case, you sure are smart.
    Mike
     
  15. legg

    legg Guest

    It doesn't really matter when, how, or why insulation between strands
    is achieved and the voltage levels presented are extremely small, so
    polymers are really overkill.

    Note that complete isolation is not required, simply a degree of
    effective isolation, most of the time, between adjacent inner and
    outer stranding, as these will swap over, by design. If 80% of the
    skin current is forced back into the bundle, then an effective litz
    action is performed.

    Litz is most called for where layering cannot be avoided. Obviously
    turn and layer insulation has to be provided by something a little
    more predictable. This isn't hard to do.

    RL
     

  16. It matters if it is not complete, and it touching other conductors along
    the way (and it will) causes problems. If not detrimental parasitics, in
    fact.
     
  17. JosephKK

    JosephKK Guest

    It is not braided in the sense that hair is braided, it is twisted in increasing
    levels much like rope is. Say 3 strands twisted, in groups of 7, in supergroups
    of 3, in hypergroups of 7. Though this clearly would not be optimal.
     
  18. qrk

    qrk Guest

    As a gross rule of thumb, proximity effect dominates under 1MHz. Above
    1MHz, skin effect will come in to play. Most of my work designing
    power pulse transformers is in the 50kHz to 800kHz range. Checks with
    an impedance analyzer (HP 4195 and 4194) have shown that the equations
    given in E.C. Snellings "Soft Ferrites" book are pretty good. E.C.
    Snelling and Giles have another book on transformers. I've forgotten
    the title, but it also covers proximity effect.
     
  19. qrk

    qrk Guest

    Proximity effect is little known unless you design transformers. It is
    rarely taught at the uni. An excellent reference is "Soft Ferrites" by
    E.C. Snelling. You can usually find this book at university libraries.
    There's another book, "Ferrites for Inductors and Transformers" by
    Snelling and Giles on transformer design. Soft Ferrites isn't the
    easiest read, but the information towards the rear of the book has all
    sorts of useful information about winding configurations. The program
    "Magnetics Designer" by Intusoft also deals with proximity effect.

    Frequencies under 1MHz, proximity effect is dominant. I have run the
    calculations and tested transformer designs with impedance analyzers
    (HP 4195 & 4194). The calculated and measured come out fairly close.

    Bunched conductors are parallel insulated conductors (magnet wire)
    which are twisted together, just like stranded hookup wire from
    Belden, but fewer twists per inch. In a pinch, I'll make my own
    bunched conductors and twist the bunch using an electric drill. For
    production, I use Litz wire from MWS. I use Litz since they won't make
    bunched conductors for me. Don't know why since this is considered one
    bunch in a Litz construction. Since we don't make that many
    transformers, the 5 pounds of wire we get will last a decade or two.

    On the practical side, the bunched conductors I have made/used aren't
    much different from commercial Litz wire in my tests making 5kW pulse
    transformers for 400kHz service. I'm sure my office made bunched
    conductors weren't perfectly in the same position at an equal time.
    Holy crap, that's a lot to say! Just twist the stuff and everything
    will be happy.
     

  20. E X A C T L Y !

    A bundle of individual EM fields from individual strands does NOT
    generate a field that is the same as that of an equally sized solid
    conductor.

    In fact, in a solid conductor, conduction CAN be pushed to the outside
    of THAT conductor. In the case of a bundle of individual conductors, the
    individual EM fields generated are NOT capable of forcing ANY of the
    center conductors' electrons to the outer shell of the bundle, and from
    within an individual conductor, IF the push was occurring, it would only
    'push' those electrons out to one side of it, but it would still be 'out'
    at the skin, where it belongs.

    More likely a mag wire manufacturers ploy to sell "specially
    configured" spools at exorbitant prices over cost.

    We could have been making our own all along.
     
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