Re: Aluminum vs Copper Primaries

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

Original poster: jimmy hynes <chunkyboy86-at-yahoo-dot-com> 

Hi,

--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: Harvey Norris <harvich-at-yahoo-dot-com>
 >
 > We normally think that since Aluminum has a higher
 > resistivity, that more losses might be involved in
 > using an aluminum primary vs that of a copper one. I
 > get about a half ohm for 100 ft of this 1/2 inch
 > diameter aluminum cable I am using.
 >
 > The chart at
 > http://hot-streamer-dot-com/temp/skindepth.gif
 > shows that copper is 1.7 micro-ohm/ cm
 > (I assume that is supposed to be micro-ohm/cm^2 to
 > express area)
 > and that aluminum is 3.02 micro-ohm/cm^2
 > which would be a value showing that Al has 77% more
 > resistance then equal volumes of Cu
 >
Hmmm... Those numbers are a little different than the ones I saw

http://www.microwaves101-dot-com/encyclopedia/calsdepth.cfm
http://www.microwaves101-dot-com/encyclopedia/conducting.cfm

 > But when we compare the skin depth at 200,000 hz we
 > find that copper has about .06 inch vs aluminum at .08
 > inch, so Al has 33% more penetration from the currents
 > at high freq then does copper.
 >
 > In viewing the trade-off here should we then think,
 > that given a sufficiently wide circumference of the
 > primary itself as a cross section, that aluminum is
 > actually only about 44% more less efficient for high
 > frequency conduction currents then copper?
 >

I think so. With the other numbers, I get 58% worse at DC and 26% worse at 
high frequency.

 > This also raises the question of  what is the % of
 > time periods involved when the primary is actually in
 > high frequency vs the time when it is in source
 > frequency conduction. Isnt the high frequency time
 > period small compared to when the source frequency
 > currents are acting? This would mean that aluminum
 > would appear closer to 77% more resistance.

Do you mean the current charging vs the current while the gap is 
conducting? The charging current
is only a few milli amps, and is insignificant even though it takes place 
for more time. The high
frequency current is the only current that matters.
 >
 > These are probably irrevalent issues, but I am
 > wondering since I constructed a primary using wider
 > circumference aluminum power cable, designated as 3/0
 > gauge about 1/2 inch in diameter, but it is also
 > stranded with about 18 strands distributed in the
 > grouping. Will the skin effect still take place on
 > each of these strands, even though they are adjacent
 > to each other with their surface areas coming into
 > contact?

Stranded cables look just like solid cables to skin effects.

 >
 > Finally is the primary resistance not something to be
 > concerned about, since the losses involved in the
 > actual primary arc gap would be far greater then the
 > losses involved on the lines themselves?

The spark gap loss is probably much larger.
 >
 > Sincerely HDN
 >
 >


=====
Jimmy