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Re: The 1500t secondary myth



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.