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Re: Copper strap...
Hi Fr. Tom, all,
I'd be happy to:
> Original Poster: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
>
> If used in Tesla Coil service flat copper foil has a much greater
> RF current carrying capability because of its large surface area.
> You sometimes have to look out for corona discharge from the
> edges, however. If the foil is too thin, then the RF resistance
> increases. If I recall correctly, Malcolm Watts posted something
> about skin depth versus frequency some time ago. Perhaps he
> would be kind enough to refresh everyone's memory on this topic
> as it applies to Tesla Coils.
You can define 1 skin depth as the depth in the conductor at which
the current has fallen to 1/e of its total value.
As a general rule,1 skin depth in copper = 66/SQRT(f) mm. I
say general because resistivity of the material is factored in and it
varies for different copper alloys and I think degrees of temperance..
My general preference for winding secondaries to obtain high
Q's is to go for a minimum wire diameter of 3 skin depths for a 1:1
spacewind and a minimum of 5 skin depths for a closewind at Fr.
The larger the surface area per unit length of the conductor, the
lower its resistance. For secondaries it is often rightly argued that it
is often the least important factor in obtaining long sparks but if your
goal is to obtain a high voltage step up without breakout in a CW coil
it is a good idea to heed this factor. For primaries, it can have
considerable influence on their efficiencies. A really good primary
and capacitor throws all the onus back on the spark gap.
Regards,
Malcolm