TC Optimum Coupling (was RE: Auto Quenching - OOPs!! forget that one ;-)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Terry, Antonio, Marco, all -

Tesla coil theory and simulations must be used with caution. Increasing the
K factor of Tesla coils can increase the secondary volts output? Reducing
the number of secondary turns can increase the K Factor. If you continue
with this reasoning you might believe that you could use only a few
secondary turns for big sparks or secondary voltages. See below.

In my Tesla Coil Design Manual that was written several years ago BI (before
internet)the statement is made under Section 15 - K Factor   "It is obvious
that increasing the coupling will increase the K Factor. It is NOT so
obvious that reducing the number of secondary turns will also increase the K
Factor."   In other words you might deduce that reducing the number of
secondary turns will increase the K Factor, reduce losses, increase Q
Factor, and increase secondary voltage gain. Is this correct? Well, not
exactly.

But if the above is not correct it means that the present mutual inductance
equations are not correct because the mutual inductance is used to find the
K Factor. Not likely.
  K = Lm/(sqrt(LpLs)).

Marco Denicolai says to "increase K as much as possible" (theory). But how
do you determine this parameter for a real world Tesla Coil? Real world
Tesla coils generally mean compromises have to be made.

All this can be checked out with the computer program
    JHCTES VER 3.3 (change only number of sec turns and click Calculate)

Click on   http://www.mgte-dot-com
Click Tesla, JHCTES Books, and JHCTES Ver 3.3 at bottom of page.

You can't get something for nothing. When you reduce the number of sec turns
note that the JHCTES program changes many other parameters to keep the TC
system in TUNE. The JHCTES spark length (sec volts) actually decreases when
the K factor increases because of these other parameter changes. Only a few
secondary turns will not give you big secondary voltages.

It is obvious that the TC designer has to make compromises in selecting his
components to find the optimum design. This means  juggling about 30
parameters that normally could not be done by manual calculations. However,
the calcs can be easily done by using computer programs that produce real
world TC designs. Real world programs must also coordinate enough parameters
for a complete design because the parameters are so interdependent.

The JHCTES Ver 3.3 program includes only the minimum major parameters
necessary to start a design for a classical Tesla coil. The JHCTES Ver 3.3
computer program is based on real world test data. The program is only as
good as the data. This is why the program is being continually upgraded.

John Couture

-------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, August 29, 2002 8:49 PM
To: tesla-at-pupman-dot-com
Subject: Re: Auto Quenching - OOPs!! forget that one ;-)


Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
>
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi All,
>
> Disregard yesterday's post and my ideas about "auto quenching".  As it
> turns out, the effect does not exist.  It was just a computer modeling
> error on my part.  The way I had it set up allowed the firing voltage to
> vary as I changed the coupling.  As I worked with my coil last night it
> seemed that something was really wrong with the idea.  I churned through
> the models today and found the problem.  The proper peak voltage vs.
> coupling graph, even with all the losses, looks like this:
>
> http://hot-streamer-dot-com/temp/OLTC08-29-01.gif
>
> Probably exactly what Marco and Antonio would agree with ;-))

Now it's ok. Even with high losses, the theory says that high coupling
invariably leads to smaller losses, higher output voltage, and the
system behaving closer to the lossless case. With high coupling the
special values of the coupling coefficient are important, as can be
seen by the ripples in your plot, corresponding to 0.18 (mode 5,6),
0.22 (4,5), and 0.28 (3,4). The next ones would be 0.38 (2,3) and
finally 0.6 (1,2), counting only the main line (there are infinitely
many other modes between these, with complete transfer at the second
or other notches). The behavior that Marco mentions, where a slight
detuning of the system leads to greater voltage gain (but incomplete
energy transfer) appears more clearly at the last high coupling
levels, but always exists in some degree. Of course,
with losses the optimum values of k are different, but not by great
amounts until the system is totally degenerated. With high coupling,
the effects of losses are less significant, since the energy transfer
completes before the losses have time to distort significantly the
waveforms, and the lossless theory applies well enough for design
purposes even in extreme cases. Simulators use the theory, and they
must show this too.
As you could see, simulators can lie, but not Nature.

Antonio Carlos M. de Queiroz