Thread-topic: What´s the current standpoint on quarter wave versus lumped secondary modeling
I might also mention that "javatc" shows the current and voltage distribution on the secondary from bottom to top.
Steve
----- Original Message -----
From: "Antonio Queiroz" <acmdequeiroz@xxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Sunday, May 26, 2019 8:00:02 AM
Subject: Re: [TCML] What´s the current standpoint on quarter wave versus lumped secondary modeling
Em 19/05/2019 13:37, jan@xxxxxxxx escreveu:
> 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.
>
There is no mistery about this. A Tesla resonator is really a
distributed circuit, but behaves quite precisely as a lumped circuit.
The current is higher at the bottom of the coil, and gradually
diminishes to a minimum at the top. The minimum is close to the maximum
if the terminal capacitance is large and small if the terminal
capacitance is small. If the "self-capacitance" of the coil is reduced
to a single capacitance added to the terminal capacitance it's possible
to consider the current uniform along the coil with little error, with
the charge that gradually accumulates along a real coil considered
concentrated in the lumped self-capacitance. A better model can be
created by considering the coil split in several sections, each with its
inductance, mutual inductance to the other sections and capacitances to
ground and to the other sections, with losses added too, but this is
useful just for simulations. A simple lumped LC model is enough for
calculations, with something adjustable added to allow precise tuning.
Consider also in the case of thermal imaging that the bottom of the coil
is close to the primary coil, that can get really hot, while the top is
close to the terminal, that can act as a heat sink. The thermal image
can appear exaggerated due to this.
Antonio Carlos M. de Queiroz
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