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Re: [TCML] What´s the current standpoint on quarter wave versus lumped secondary modeling

Hi Jan,

There isn't any real dispute between the two views. Any "debate" has more to do with how accurately one wishes to model the real-world behavior of a TC resonator. A truly accurate resonator model must take into account the coupling of E and H fields between turns within a helical winding, and E-fields between the resonator and topload, and its surroundings. The resulting solutions are complex, are not closed-form, and are virtually impossible to solve without intensive computer modeling. A resonator is a deceptively complex device, and truly accurate models have only fairly recently (last 30 years or so) become available.

A lumped LC model of a resonator:topload is considerably simpler... and its also considerably less accurate. For example, the lumped model doesn't describe internal voltage and current distributions, resonator high-frequency (harmonic) behavior, nor resonator impulse behavior. Fortunately, most of these behaviors are usually not critical to the operation of a typical Tesla coil. The lumped model's major advantage is that it provides a simplified, closed-form approximation that can be easily used in the design and construction of efficient pulsed and CW Tesla coils... as long as they are operated at, or near, the resonator:topload's fundamental operating frequency. Current TC simulators, such as Bart Anderson's JavaTC, JavaTC3D, FanTC, and JavaDRC, combine aspects of both models to some extent. These are very useful and accurate design tools for the practical hobbyist. Although the tools don't accurately describe the rich spectrum of behaviors seen in helical resonators, they really don't have to to be effective as TC design tools.

As Kurt Shraner suggested, you may wish to check out the extensive information about TC resonators on Paul Nicholson's Tesla Secondary Simulation Project (TSSP) web site. This site reflects the multi-year effort of many coilers around the world who pooled their efforts to better understand TC resonator properties and behavior. I suspect that you'll find that Paul's writing style is considerably more readable and understandable than Dr. Corum's papers. See:

Your thermal measurement provides excellent evidence of nonuniform current distribution through your secondary. This is in general agreement with the predicted current profile for a typical resonator and toroid topload. See Example 8 on the following "Example Voltage and Current Profiles" web page:

As can be seen in the V and I charts for example 8, although the voltage profile is approximately linear, the resonator current peak occurs at a point above the base of the resonator, accounting for higher joule losses around the base. The region of highest primary:secondary energy coupling also occurs within this region of the secondary.

Best wishes,

Bert Hickman
Stoneridge Engineering LLC
Woodridge, Illinois, USA
+1 630-964-2699
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

jan@xxxxxxxx wrote:
Hi, I recently made a very simple measurement on my coil
www.sthlmteslacoil.se <http://www.sthlmteslacoil.se>  with my
IR-thermometer. After a few minutes of running, the top of the secondary was
at room tempoerature (20 degrees), while the bottom part was at 30 degrees
celsius. I can´t find any other explanation besides that the current could
be much higher at the bottom part and therefore cause local resistive
heating of the magnet wire.

What is the current standing in the debate about tesla coils being quarter
wave resonators as opposed to simple lumped LC-circuits? If they are quarter
wave resonators the current would be much higher at the bottom, but not if
they could be modeled as lumped circuits.

The main documents I have found from when the debate was hot twenty years
ago are these:



They both seem quite convincing to me, but are totally copntradictory. What
is the current standpoint on these issues? Are there any alternative
explanations to the heating of the bottom part of my coil?



Stockholm, Sweden

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