Al coil AC resistance

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

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

The use of aluminum conductors for a Tesla Coil primary has often been
brought up, and the response has generally been that skin effect would
force the surface currents into the oxide layer, resulting in a high AC
resistance and losses.

I finally got a round tuit and built myself an aluminum primary out of
Radio Shack's finest 0.1" thick aluminum ground wire.  I made the
geometry and inductance identical to the other coils that I constructed
in my primary AC resistance experiments, and tested the AC resistance
over the range of 40-800KHz.

Below about 400KHz, I saw no evidence of resistance disproportionate to
the coil's DC resistance.  While there are still several reasons to
favor a copper primary over an aluminum one, (ease of
soldering/splicing, availability, and integrity of clipped-on tap
connections), I don't believe that skin effect losses is one of them.

Full data on the experiment may be seen at
http://www.laushaus-dot-com/tesla/primary_resistance.htm

I also tested the consequences of having unused outer turns on a primary
inductor.  The results were not extremely dramatic (at least for the
case of 5 unused turns), but resistance was slightly higher with the
unused turns.

Regards, Gary Lau
MA, USA