Re: AWG vs. Diameter

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Chris,

A complex question :-))

Due to skin effect, RF currents only travel on the outer layer of wire.  For
copper, that thickness in inches is:

D = 2.602 / SQRT(F)

So at 150 kHz, the thickness of the layer of current flow is only 0.00672
inches.  You could use very thin copper tubing indeed without noticeable
effect.  Taking the skin depth into account and doing the math to find the
conductive area of each conductor:

1/4 inch tube = 0.0051345 square inches
#6 wire = 0.00327 square inches.

So the tubing has 57% more conductive area that the wire.

However, let's consider the coupling.  Using Dr. Rzeszotarski's program on a
coil with dimension just like mine...

1/4 tubing = 0.198
#6 = 0.196

So the wire has slightly less coupling, but nothing to worry about.

Then, as the recent discursion about the inner turns getting hot showed, we
have to consider proximity and eddy current effects.  Unfortunately, I don't
have an answer there.  I would think the thinner wire would be better, but I
don't really know.

In general, people tend to find that the thicker tubing does better than
thinner wire.  We always attributed that to the differences in skin depth but
these new proximity and eddy current factors may matter a lot too.  Primary
losses can really eat up a coil's performance so this is pretty critical stuff.

Cheers,

        Terry


At 06:18 PM 3/16/2002 -0500, you wrote: 
>
> Hi Folks! 
>
> Can anyone tell me the difference between 1/4" copper tubing and say, 6ga
> wire? How do they compare in current carrying capability? Just curious 
>
> Chris W