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[OT?] Soldering Litz wire for high frequency tranformer (1500W DC-DC converter)

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  • #31
    Here is the basic idea for having four windings of four turns each:



    But there is still the problem of connecting the turns in series. Here are some concepts:



    If I could run this at 400 kHz, I could get 16 volts/turn, but that is really getting into state of the art for large transformers, far beyond what I feel comfortable designing.

    Here is a view with another idea, using 0.032" x 0.125" bus strips making a spiral winding on end. This forms a shape something like a slinky. It would be a nightmare to solder all the pieces together, however.

    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

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    • #32
      whats wrong with a soldering torch?

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      • #33
        A couple suggestions.......

        1) if the strips are much thicker than the skin depth, the AC resistance may be over 16x higher than the DC resistance with those coils. It's hard to explain adequately without writing a huge post, but there will be counter-currents running in the foil because of the thickness, and the fact that the field cannot go through the strips. Those counter-currents will have large losses that increase the effective resistance a lot more than one would expect.
        If you look on the TI site, they may still have the paper by Lloyd Dixon that explains how skin depth affects AC resistance. I'll see if I can find a copy and get the exact title.

        2) Narrow coils like that have poor coupling to the core and much more leakage inductance than even wire spread out over the full width of the winding window. Better to have thinner foil that fills the width. If they are always in series, that would turn them into a spread-out coil, but if not, they may not be as effective. And, being narrow, they MUST be thicker to get the cross-section, so you fall afoul of the skin depth issues

        Originally posted by dian View Post
        whats wrong with a soldering torch?
        Huge, and hard to control around that insulation and thermoplastic bobbin, if by "torch" you mean something with fire coming out of it.
        CNC machines only go through the motions

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        • #34
          I found the article:

          http://www.ti.com/lit/ml/slup197/slup197.pdf

          Very enlightening although somewhat discouraging. I was surprised that the eddy current and skin effect could be that great, and also the principle that multiple parallel flat conductors may not actually reduce AC resistance. It almost seems like black magic or witchcraft might be needed for high frequency transformers.

          There is a lot to absorb in that article, and frankly I will probably never fully understand it. But it does give me some ideas about how to proceed. Thanks.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

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          • #35
            Yep, that's the one.

            It sure is counterintuitive at first glance, although when you think about the reasons, it becomes pretty clear why it happens. Doesn't mean you have to LIKE it, though!!!!!.
            CNC machines only go through the motions

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