more about Litz wire

Andre' Kesteloot akestelo@bellatlantic.net
Thu, 13 Apr 2000 15:26:23 -0400


Talbot Andrew wrote:

> Well, Gamal and Paul between them hit on the solution.  It definitely
> appears to be proximity effect causing extra losses for the Litz wound
> coil.  I re-measured both at 80kHz and the Litz one came out
> significantly better at 42 as opposed to 30 for the single layer one.
> The losses caused by proximity effect obviously dominating the tiny
> improvement from not very efficient Litz winding with each strand still
> 4 - 5 skin depths in diameter.
> Dielectric loses were insignificant, the former material barely got warm
> in a Microwave oven.
>
> G4MD :
> >Would not increasing the Q
> >lead to higher circulating currents at resonance, thus greater
> >heating? Unless of course the effective x-sectional area of the
> >conductor was increased in square-law relationship to the increase in
> >current!
>
> Q is only the relationship between loss resistance and reactance.  A
> higher Q means lower series R and must mean lower loss.  It all falls
> out in the maths :-(
>
> ZL2CA:
> >You did not report in your findings if the Litz wire coil ran cooler
> >than the single wire coil, but I am presuming it did.
>
> I did not even bother loading up, it was obvious from the Q measurement
> it would dissipate more so not worth trying.
>
> --------
> I wound a new coil as Gamal suggested.  Using 68mm diameter drain pipe
> (I bought a 2m length for the grand sum of 2-60 - anyone want some coil
> formers :-)    42 turns of 0.8mm tinned wire spaced at 3mm over a length
> of 130mm.  Q now twice that for the original single layer coil at 250.
> I couldn't use the spacing to conductor diameter ratio of 1.4 to 2.2
> that Peter suggested as it was difficult winding the bare wire onto the
> smooth former with a spacing much less.
>
> It was very instructive comparing the measured loss resistance from Q
> value with that calculated from conductor length, diameter and skin
> depth.  For both single layer coils the actual loss resistance was only
> about twice that calculated.  Considering what other loss mechanisms are
> present, this result is very satisfyingly close.
>
> Now I suppose I'd better actually have a QSO on topband although I've
> still got to measure the antenna properties on that band and compare
> them with the values measured when it was first built for 73/137.
> Anything to avoid going on air !
>
> All the fun is in making things work rather than using them when they do
> :-)
>
> Andy  G4JNT
>
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