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Re: Skin effect and aluminum question (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Feb 1998 08:40:53 -0800
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Skin effect and aluminum question (fwd)
Tesla List wrote:
>
> ---------- Forwarded message ----------
> Date: Fri, 13 Feb 1998 08:40:26 -0700 (MST)
> From: Chip Atkinson <chip-at-sophie.bolix-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Skin effect and aluminum question
>
> Greetings,
>
> I have seen it mentioned on the list that aluminum is a poor choice of
> conductor because the oxide layer that forms on the surface is an
> insulator, and that if, for example, your oxide layer is 0.001" thick and
> your frequency is such that you only have current going through the top
> 0.006" of the conductor, you will then lose 1/6 of your available conductor.
>
> However, I fail to see the difference between Al2O3 on the surface acting
> as an insulator and a coat of varnish on the surface. Both the Al2O3
> coating and the varnish coating don't conduct, and are unaffected by
> magnetic fields.
>
> Can anyone convince me that I'm wrong? I am aware that the aluminum
> conductor may provide more resistance at connections because the
> electricity has to penetrate the oxide layer though.
>
> Thanks!
>
> Chip
Chip,
As long as the overall thicknes of the aluminum is much greater than the
skin depth, the presence of a thin oxide layer has NO impact on skin
effect/skin depth. The resistivity of alloyed aluminum wire is about
1.8X that of copper, and the resulting skin depth will be about 1.3X
that of copper at equivalent frequencies. You can use aluminum tubing in
your tank circuit with relatively little effect, since the overall Q of
the primary circuit will still be dominated by the gap. You could also
use aluminum wire in the secondary if you've got no other choice, but it
will approximately halve the secondary's non-breakout Q - so for best
performance use copper wire in the secondary.
Safe coilin' to you, Chip!
-- Bert --