Re: Aluminium Wire (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sat, 29 Sep 2007 16:38:59 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Aluminium Wire  (fwd)

I don't dispute that copper is the best choice for a primary conductor.
It is for several reasons, lower resistance by a factor of 1.6 for same
conductor diameter being the best one.  Solderability and availability
also better.  But I don't believe that the resistive behavior of
aluminum changes at RF frequencies in a way that warrants advising folks
to avoid it at all costs.  The testing that I did measuring the AC
resistance showed NO frequency-dependant difference in resistance beyond
the difference in DC resistance.  Calling aluminum wire a loser just
because it exhibits a 1.6X higher resistance over same-sized copper wire
is like saying 14 gauge wire is a loser because it also has 1.6X (yes,
what a coincidence!) the resistance that 12 gauge wire has.  So a 12
gauge aluminum primary will behave identically to a 14 gauge copper
primary, regardless of frequency.  It's all relative.

My point is that blanket statements that aluminum is bad at RF
frequencies leads folks to silly behaviors, like saying that RSG
electrode holders should not be made of aluminum because RF currents are
involved.  

Gary Lau
MA, USA"

	Been watching this discussion and I agree completely even though some eminent authorities believe otherwise.  I've made several primaries using aluminum refrigerator tubing and don't think there was, or could be, significant performance degradation.  The coils ran at input powers of just under a kW and the primaries didn't get warm, the real practical test of power loss.  Even 50 watts of loss would have really warmed these things and they stayed cool.  The losses in the gap, which did get hot, were much greater and I suspect this always the case.  To me the main reason for avoiding aluminum would be the difficulty in making reliable taps on the coil. It would certainly be easy to make a couple of wire wound primaries [say #10 wire] and measure the relative Q's at say 200 kHz.  Although I'm not ambitious to do the experiment [I do have the wire] I'm certain the results would prove that both had sufficiently high Q that the loss difference wasn't important.

	In airborne microwave equipment aluminum [and even magnesium] waveguide is commonly used with negligible loss in reasonable lengths.  I've seen sections removed from service which were badly corroded on the inside due to condensed moisture resulting from careless installation of gaskets and their loss wasn't significant either.  They were removed because of physical damage [idiots walking on them] and not electrical reasons.

Ed