Re: The 1500t secondary myth

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

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.