Re: The 1500t secondary myth

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>


I also built a 3,000 turn coil last year.  I saw no performance gains
(actually a bit less) that our normal 1,400 turn coil.  Both coils were
operated with the same cap size (same energy input) and same size topload,
with a non-sync rotary gap for comparison.  The 3,000 turn coil performed a
bit less than the 1,400 turn coil.  I think the resistive losses began to
get too high.

Power was provided by the same 14.4 kV PT set for 250 mA output.  We
monitored input current to set output with an adjustable power reactor.

My conclusion was the 1400-1600 turns range provides the best coil
performance.  Beyond this nothing is gained.

I wish to note our experiments were conducted with classic design TCs and
not a magnifier type design.

Dr. Resonance

Hi,

The "model" for streamer impedance we use so much (220k + 1pF/foot) was
derived from testing.  It is almost bazaar how well it works in so many
situations and with such a large range of coils.  We know that before
breakout, the Q is very high and then once an arc path in the air is
established the Q drops way down.  But the initial high Q situation is a
very brief part of the whole grown streamer.

It does seem that for working coils, the models do give very good and
reliable results even though they seem so "simple".  I am starting to think
that the streamer's impedance may be far more stable and predictable that
we realize.  If that was not the case, the models should fail or deviate
far more than they do.  If you have not already seen it, there is a paper
on this at:

http://hot-streamer.com/TeslaCoils/MyPapers/modact/modact.html

Dan's DRSSTC-II book also repeats much of this "real vs. modeled" analysis
for his solid state coil and the models still seem to work very
well...  So, the models do seem to not only work, but they are telling us
that streamer impedances just are not that complex from a "big picture"
point of view.  Indeed, the more we look, the simpler it all seems once we
pin down what is "really" going on.

We almost always use lumped models ;-)  Not really because they are so
easy, but in the end they do work very well despite the inner harmonics and
all going on in the resonator.  The "wire length" idea does not really
apply since the coil, unlike a long antenna, has all of it's turns closely
magnetically coupled to each other.  The currents in the secondary really
are very uniform in many ways as in a simple lumped coil as shown here:

http://hot-streamer.com/TeslaCoils/MyPapers/topsync/topsync.html

Of course, if one does want to delve into the harmonics and fine details of
a coils nodes and all, this ground breaking work by Paul is it!!:

http://www.abelian.demon.co.uk/tssp/

http://hot-streamer.com/temp/pn2511.pdf

http://hot-streamer.com/temp/pn1401.pdf

Paul's fine work has now been incorporate into the latest Tesla coil design
tools in the form of Paul's GEOTC 2.7 tools in Bart's FANTC and JAVATC coil
design programs.

http://www.classictesla.com/

http://www.classictesla.com/fantc/fantc.html

http://www.classictesla.com/java/javatc.html

So there are powerful tools out here now that have certainly gone far
beyond "lumped theory".  But lumped theory still works for many many things
as well just as the highly complex non-lumped models say it should.  "I"
don't worry about "wire length" in designs at all other than being sure I
have enough wire left on the roll to wind the coil ;-)  The 1500 turn thing
is just a nice mid point between say 400 and 3000 turns were successful
coils have also been made...  When a person asks how many turns to use, we
"know" 1500 will work...  That number also seems to fit into the range of
NST ratings and capacitor values well.  But there is no great "limiting
theory" there other than simple parts availability...  I bet one could make
a nice coil at say 150 turns and 10,000 turns if one really tried...

Computer simulations such as we use for DRSSTC work are indeed using lumped
coil models.  But there, we are not concerned with anything other than how
the coil presents it's loads to the driver circuits.  In that case, the
lumped models work just fine.  Most DRSSTC, LTR, OLTC type Tesla coils owe
there existence to computer models and, yes, they are all linear lumped ;-))

Just five short years ago many people believed that Tesla coils were too
complex and "mysterious" for computer modeling and simulation to work.  It
was not easy and it took a LOT of work by many many people, but today they
DO work!!  In fact, unless one is really careful and has really good test
equipment, the models are more accurate than one can "measure" now!!!

It does seem odd though...  As I work on my DRSSTC project, the "coil" part
is a trivial matter...  All the work seems to be in designing 5V logic
circuits and ordering parts from DigiKey...  There is no doubt, computer
modeling and software have changed the sport of Tesla coiling
dramatically!!!  The DRSSTC may do to spark gaps, HV transformers, and
variacs what the MMC did to rolled oil caps and make them "extinct" very
quickly...  I think these years will be remembered as the time when modern
engineering and Tesla coiling "joined together" to change
"everything"!!!  Tesla would still recognize the primary and secondary
coils as well as the top terminals and figure out the primary caps
quickly.  The basic "machine" there is the same.  However, everything else
from his day is gone now...  Of course, its been 105 years since ;-))  Of
course, Tesla didn't have "work on web page" on his Tesla coil todo list
either :o))

Cheers,

         Terry






At 07:06 AM 12/14/2004, you wrote:
>Looking for ideal impedance characteristics is a fine thing to do,
>however..
>The impedance formula found in text books are derived on the basis of
>lumped analysis.
>Now if we are applying these formulae to Resonant transformers we are
>pre supposing that resonant transformers are also lumped. If resonant
>transformers were lumped then it would not be possible for nodes to
>form along the length of an inductor as this implies a non uniform
>current, an immediate violation of the lumped assumption. One can then
>conclude that the classic impedance formula (as is) is incomplete when
>applied to Tesla coils as it lacks spatial components.