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Re: Top Load Optimizing - Q?



Terry,

Thanks.. you just cleared up quite a few misconceptions a newbie can make
(this one did anyway) concerning efficient coil design.  That still leaves
one unanswered question however, one I was hoping Rodney's original article
answered.  Others on this list seem to suggest a coil should run the largest
possible torroid a coil's design will support, and that the longest
streamers will result from a large-as-possible top load to delay breakout.

So... how do I predict the (nearly) optimized torroid size for my coil given
my power source, tank capacitance, secondary and primary design?  Is there
an accepted way to do this beforehand, or must I simply try larger torroids
until I can either no longer tune without adding tank capacitance,(run out
of primary turns) or until I can no longer achieve streamer breakout?   << 
Give me a quick hint here.  Thanks.


Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi Jim,

At 10:08 AM 03/17/2000 -0500, you wrote:
>In a well-written article, Rodney posted the following:
>
>"The main concept with top-load design is matching it to the secondary
coil.
>With capacitive/reactive tuned circuits, the way to obtain zero
impedance is
>to match your capacitive reactance with the inductive reactance."  The
>complete article may be viewed here:
>
>http://www.geocities-dot-com/ResearchTriangle/Campus/9367/tuning.html
>
>He goes on to calculate capacitive reactance of the torroid top load,
and
>states that the goal is to design your top load so that this capacitive
>reactance cancells out the native inductive reactance of the secondary.
He
>goes on to make the following statement:
>
>"The secondary coil is best described as an air-core inductor ? for
that
>matter, any coil of wire is known as an inductor. As capacitors have
>capacitive reactance, inductors have *inductive* reactance.  The
formula for
>calculating the inductive reactance of your secondary coil is  X(L) = 2
* Pi
>*  F * L ..."
>
>My question is this:  Programs like Wintesla calculate both the
inductive
>reactance of a secondary AS WELL AS the native capacitance of that
>secondary.  Should I attempt to design my coil such that total
capacitive
>reactance (secondary + toroid) cancells out the inductive reactance?
Or do
>we ignore the native capacitance of the secondary?
>
>It's not the size of the spark, it's the frequency.
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I think there are a few 'technical' inaccuracies in the article so let
me
clarify if I can.

When any capacitor and inductor are tuned to their resonant frequency,
the
reactance of the inductor will be exactly the opposite of the reactance
of
the capacitor and they WILL cancel.  That is the fundamental definition
of
resonance!  In a way, the article says this but it seems rather round
about
and perhaps misleading.  You can pick any inductor and any capacitor and
they will have a resonant frequency.  The only variable is "what" that
frequency is.  You really can't have a tuned coil where the two
reactances
are NOT cancelling, so don't worry about it.

What is important is that your top terminal and secondary inductor are
tuned to the same frequency as your primary capacitor and primary
inductor.
The programs will help insure that you don't get the tuning so far off
that you can't tune it.  We often here of people saying that they have
tried tuning their primary in every place and they only get a one inch
spark.  When we dig deeper and do all the calculations, we find that
there
primary coil is not able to tune to the frequency of their secondary
coil.
They usually have to add capacitance or more turns to the primary
circuit
which is something they wish they had known before.  They KNOW when they
get it right ;-))  The only heat loss that really matters is that when a
coil is out of tune, ALL the energy goes into burning up the spark gap.
When they are in tune, half that energy goes into the arcs (and the
other
half still tries to burn up the gap ;-)).

There is no right or wrong way to make a Tesla coil.  As one looks at
the
many coils around the net you can see that we all make coils like we
feel
or with the parts we can find in our areas.  However, there are limits
that
a working coil has to stay within.  Defining and calculating those
limits
can be extremely complicated and leaves even the best of us gasping at
times.  However, the programs allow the messy calculations to be done by
anyone with a little knowledge.  This list can hopefully fill in the
details and questions.

I should mention that the primary inductance and capacitance can be
calculated easily with the equations and programs.  The secondary
inductance and "self capacitance" (the natural capacitance of just the
secondary coil) can also be calculated accurately.  The bare toroid in
space all by its self can also be calculated.  However, when the top
terminal is placed next to the secondary, the calculations fall apart.
You
may get lucky and get fairly close or have enough tuning range that you
will still be able to tune but don't be surprised it the coil's final
frequency does not closely match the simple calculations (it will be
higher).  Usually the programs will be close enough however.  If one
really
wants to calculate the final frequency, programs like E-Tesla5 will
crunch
the numbers for a few hours and tell you to within 5%.  Just be glad you
were not here when we thought we had to solve transmission line
equations
or use Smith charts to design or tune coils ;-))

The advice I give to newcomers to the hobby is to look around on the
webring and find a coil that you would like to have and you think you
could
build (and that works well ;-)) and do what they did.  No need to
reproduce
every last screw in the exact right place but just follow the general
dimensions and such.  As you build and learn you will catch on very
quickly
to many things.

Everyone has their own way of doing things and they all seem to work.
Some
study every equation for hours and learn every detail they can before
ever
touching a tool.  Others have it all built and ready but no idea how to
make it run...  Hardly anybody builds their first coil perfectly the
first
time (except Finn! ;-))  They all eventually get there, the only real
rule
is don't get electrocuted!!

Hopefully this gives you ideas and helps explain.  This is a complex
hobby
and there is a lot to know but that's where the fun lies ;-))

Cheers,

Terry

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