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Re: Top Load Optimizing - Q?

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