Re: skin depth/Aluminum Primaries via Marx Gap

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

Original poster: Harvey Norris <harvich-at-yahoo-dot-com> 


--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: Jim Lux <jimlux-at-earthlink-dot-net>
 >
 > The handy thing to do is to remember the skin depth
 > at a standard frequency
 > (100 kHz is good for TC work), and then remember it
 > scales as the square root..
 > So.. reading off the chart..
 > Ti ->1.2mm
 > Al ->.5 mm
 > Cu -> .15 mm
 > showing the usual progression as conductivity gets
 > better, the skin depth
 > decreases...
I noted on this chart, ( which takes awhile to load,
be patient) that at 200,000 hz, the skin depth is
about 26% or so higher than a copper counter part. I
have wound a large primary using Reynolds M 3/0 AL 600
Volt power cable made of aluminum. This is for testing
with "sonotube" size secondaries, of which I have a
primitive 14 gauge one already made to accompany this
primary system. Because that secondary only has about
270 winds of insulated 14 gauge wire; I have formerly
only got about 2-3 inches of arcing when it was set up
with just 5 turns of ordinary copper tubing for a
primary.  The present primary uses ~200 ft of this
insulated power cable wound in a verticle fashion,
comprising some 34 winds -at- 20 inch ht, ~ 23-25 inch
diameter. The cable itself is comprised of about 18
strands, it is not solid, at about just under 1/2 inch
diameter. My question is since the skin effect is
better with aluminum, and also since the cable is
stranded smaller diameter wires bunched together,
would this not actually be better then a 1/2 inch
copper tube primary of equivalent dimensions? This
cable was stiff and I could not get perfectly  uniform
circular winds towards the end of windings, and was
wound over a large inverted flower pot. I wanted to
make the primary appear as conical, but this was not
possible due to the stiffness of the cable.

What role does the primary dissipation of power
through resistance of that primary play? Isnt this
usually such a small quantity to be considered
miniscule? The (rf)losses involved here would seem to
be primarily through the skin effect, not actual
resistance itself which seem to measure about .57 ohms
for this ~200 ft.( Two sections of ~ 100 ft that I
scavenged from the shed) So if I have less losses with
a better skin effect, would this increase the
efficiency of the delivery of rf to the secondary?

I have also wound these sections OPPOSITELY, for
experimentation with a bifilar primary set up. I see
no reason why each primary cant be given its own
capacity to resonate, and charged up in parallel, then
essentially discharged in series, where this might be
considered as a two element "marx gap", with attached
primaries to each capacity to negotiate a resonant
frequency when the caps discharge to each other
through the two element marx gap. Since the currents
through those primaries would logically initially be
in opposite directions in the charging of two
capacities to opposite voltages; this should be
corrected for magnetic unison  on the total primary
action by having each primary being wound in a bifilar
fashion with respect to the other. If this strategy
prooves incorrect, the polarity connections to one of
the primaries can simply be reversed. Each primary
reads ~ .27 mh by LCR meter, so the primaries are well
balanced. The advantage of this system might come into
play where the higher inductances involved with the
primaries neccesitates using a smaller capacity, for
the primaries resonance projected to be in the 200,000
hz range for this 1500 ft secondary. Thus the
requirement of initially using a smaller capacity is
counterbalanced by the fact that when these are
charged oppositely in parallel, that equivalent
capacity would appear as 4 times the actual value
needed for the total primary  capacity requirements,
before it is discharged in series yeiding half less
total capacity then compared for each side alone, thus
making a four fold difference in charging capacitive
reactances, between requirements for charging action
and actual discharge. This is also the model I will
try via 480 hz AC alternator inputs to pole pig, which
gives another plus.  Less voltage input to pole pig
will then be required to get a functioning arc gap,
since the power transfer to capacities at 8 times the
frequency of 60 hz, should be 8 times as great at 8
times the frequency, neglecting the inefficiencies
brought on by using the 10 KVA pole pig at these
frequencies. Additionally the pole pig will need no
current ballasting, since the alternator itself
represents a current limited source of voltage.
Additionally I have previously tested this Marx gap
idea with a 60 hz NST using a pair of larger
inductances,just to see the feasibility of the idea;
and I found that the gap then fires at half the normal
voltage required for the same gap set up to fire in a
conventional tesla primary manner. This makes sence in
light of the fact that an dual opposing Marx gap
itself represents a voltage doubling principle.
Things are slowly coming together for the idea of an
alternator powered tesla coil, where the limitations
of input voltage and current are offset by the use of
a higher input frequency.

Sincerely HDN



=====
Tesla Research Group; Pioneering the Applications of Interphasal Resonances 
http://groups.yahoo-dot-com/group/teslafy/