Re: Secondary Turn Spacing

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Phil,

On 31 May 2005, at 19:22, Tesla list wrote:

> Original poster: FIFTYGUY@xxxxxxx
>
> In a message dated 5/30/05 10:07:07 PM Eastern Daylight Time,
> tesla@xxxxxxxxxx writes:
> "I was considering using 17lb. test nylon fishing line to space the
> turns in an effort to minimize distributed capacity.
>
>      I borrowed a solenoid optimization spreadsheet that had been
>      tweaked
> for TC secondaries, to determine the optimum configuration (lowest
> losses, least wire cost, etc.) Admittedly it was designed for the CW
> case (heat dissipation was a taken into account!), but it factored in
> every conceivable aspect of wire that I've ever seen.

Proximity losses included? A bundle of measurements I made of real
coils with and without top hats doesn't agree in general with the
spreadsheet's conclusion.

>      Long story short, space winding is lossy for TC use. How lossy,
>      and
> whether it's noticeable, depends on how drastically you space it.

What did it have to say about more spacing vs less? And more
_importantly_, are we talking about spacing with the same winding
pitch for both closewound and spacewound coils? It is obvious that if
you use the same wiregauge over the same winding length the Q will
suffer because the inductance is cut back radically for the
spacewound coil. The comparison has to be made with coils of the same
h/d ratio and same inductance or it is an oranges and apples
comparison.

> Others have already replied in this thread on the obvious tradeoffs.
>      It was interesting that least losses occurred near the point
>      where the
> skin effect was equal to the DC resistance. By attempting to lower
> losses or increase inductance by changing one parameter, theoretical
> performance suffered because of the necessary change in another
> parameter.

The ESR or skin resistance approaches the DC resistance when the wire
becomes thin enough to nullify the skin effect. In that case, the
losses will have climbed drastically because the DC resistance climbs
as well under those conditions.

Malcolm

>      FWIW, the spreadsheet predicted optimum results almost exactly
>      along
> the lines of Dr. Resonance's longtime recommendations. However,
> dropping to 1000 turns only causes a 10% performance penalty with 33%
> wire/space/cost savings.
>      The optimum wire length values were near the 1/4 wavelength
>      value, but
> this was pretty much a consequence/coincidence of the boundaries.
> Dropping to 1000 turns from the optimum 1500 range obviously works
> nearly as well. Not to mention that the theoretical optimum wire
> length diverged from the 1/4 wavelength as coil size increased.
>
> -Phil LaBudde
>
>
>
>