[Prev][Next][Index][Thread]
Re: bi-polar (center-fed) TC
On Thu, 29 Apr 1999 08:26:02 -0600, Tesla List wrote:
> Original Poster: Parpp807-at-aol-dot-com
>
> Hi all,
> I have not seen any mention on the list of a center-fed TC, so I want to
try
> to make one. This may provide considerable entertainment for all. I have
> wound 23 inches, 1480 turns, of #28 on a piece of 3-inch pvc. I used a
piece
> of schedule-40 pvc; is that my first mistake? The sked-40 pvc has 1/4-inch
> walls so the diameter of the coil is 3.5 inches.
>
> The resistance of the coil is 80 Ohms. The calculated inductance of the
> solenoid using
> (rN)^sq/9r+10 x length and the classical equation using the permeability
of
> free-space,
> (mu -naught) give a value for L of 30 mH within 0.1 mH of each other. The
> Wavetek 27XT splits the difference so I have considerable confidence in
the
> value of L. The sig-gen/counter/scope measurements show a resonant
frequency
> of 642 kHz with harmonics within a few kHz. Now, I get into trouble
because
> when I try to use the resonant frequency
> with the value for L to determine the distributed (self) capacity of the
coil
> nothing works. I
Do these measurements indicate that the coil has a natural resonant
frequency
of 642 kHz ? By this I am refering to the frequency that coil can "ring" by
virtue of its induction and internal
capacitance. I did not know a formula existed to
determine internal capacitance. Being new to the list I wanted to see what
a half wavelength match to the length of your wire was.
1480(3.5)(3.14)/{12ft/in}=1356 ft=.257 mile
Therefore the wavelength will be .514 mile
Since the wavelength = c/f then f=c/wavelength or
186,000/.514=362,091 hz
As my old understanding was a primary located around
the midpoint of the secondary coil should be designed
to resonate at 1/2 the wavelength and not 1/4. If
this stands to be then the coil primaries should made
to resonate at 362 k and not 642 k ...
In this circumstance it should be possible to
use TWO primaries as Bill Wysock has done on
his model 12. In that model he uses a field opposition
or bifilar coil arrangement. I am kind of curious why
this produces the assumed best action when the opposite
effect seems more plausible to me, whereby two
oppositely or 180 degree phases can produce a magnetic
field in unison instead of opposition. Also perplexing
is the fact the method I would use would employ a
SEPARATE capacitor for each of the 180 phasings
whereby the arc gap will consist of a connection
between them in which the configuration of the circuit
at moment of arcing then becomes the tank circuit,
represented by the two capacities in series vs the
two primaries in series, both in a parallel configuration
in a twisted figure 8 schematic. I have called this
a binary resonant arc gap and have used it in
resonating huge air inductances, which in those cases
seem to resonate easily at their natural resonant
frequency determined by their relatively high
internal capacitances. In this case a nine mile
wire coil of 56 H that should produce a quarter
wavelength frequency of around 5000 hz instead
predominated at 166,000 hz. Most unique about
this arc gap is its natural quenching ability which I
do not know will happen in application in a tesla
primary. Working space has just opened for me
and I hope to do this in the coming months and
will report results. For now its work in the garden
for spring tomatoes and peppers transplants. HDN
> expect just a few picoF; the calculated value is 0.5 picoF. My hand and
body
> capacity and
> the coil itself with its connections offer so much stray capacitance as to
> make any measurement unreliable. Can I assume that the self capacitance of
> the coil is
> just a few picoF?
>
> My next question is how do I determine the ratio of the primary and
secondary
> diameters?
> Will the equations for the coefficient of coupling (k) work? What should
the
> value be? I plan on forming 1/4-inch copper pipe so the copper pipe
primary
> will be freestanding on insulators. I assume the primary has to resonate
with
> the secondary. What range of Q
> values should I expect for these coils?
>
> Other puzzlement's: Is there an electrical difference between white and
green
> pvc?
> Will 3/4-inch stainless steel balls make a good SG? Can I use two highly
> polished brass doorknobs for a SG? The doorknobs are a little more than
> 2-inches in diameter.
>
> Thank you.
>
> Ralph Zekelman
>
_______________________________________________________
Get your free, private email at http://mail.excite-dot-com/