Re: Aluminum magnet wire?

Hi Robert,

At 09:49 PM 09/17/1999 -0700, you wrote:
>I bought a huge brand new 80 lB of #24 AWG aluminum magnet wire quite a
>long while ago at a scrap dealer. There's somthing like 120,000 feet on
>it. I wound a coil about 20" long on 4-14 inch PVC pipe for a NST
>powered tabletop coil.  I also had a similar sized coil on the same size
>form wound with #26 enamelled copper magnet wire to make direct
>comparisons. The performance with the aluminum wire coil was noticeably
>inferior!  I wouldn't use it if I were you.  Also, aluminum wire doesn't
>solder worth a darn so you have to device crimp or pressure type
>connectors, like wrapping it under a machine screw.
>However...the aluminum magnet wire is perfect for winding RF protection
>chokes!  The losses end up making a better choke for protecting NST's
>Robert W. Stephens

Just when I had myself conveinced and used all kinds of "genuine scientific
reasons" why it would work fine "theoretically", someone goes and tries it
and it doesn't work!  :-O))

My guess as to "what went wrong" would be that somewhere between when the
molten aluminum is drawn into thin wire and when it is enamel coated, there
is time and temperature available to oxidize through the 0.2mm skin depth
surface layer.

I ran models of my coil with the "theoretical" copper and aluminum wire
resistances and the output streamer power dropped from 241.5 watts to 235.2
watts.  That would be no big deal.  However, if the wire had oxidized and
the resistance was perhaps 10X, then the streamer power would be 112.4
watts!  If you meassure the resistance of your aluminum coil with a DC ohm
meter, I bet you will find it has a much higher resistance than expected.
If the aluminum wire has a considerable oxidation region at it's surace,
this is probably responsibe for the poor performance.

Since 24 Ga. wire is 0.511 mm in diamater and the skin depth is around half
that and significant oxidation did occur, it should show up obviously with
a resistance measurement.  Copper is 26.17 ohms/1000feet so aluminum should
be 1.52 times that, according to the book I have grabbed here, so that
would be 39.73 ohms/1000feet for aluminum.  If you still have your coil, a
measuremnt of the resistance per foot should show excessive resistance.