Re: TC Optimum Coupling

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

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: "John H. Couture by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
> 
> Antonio -
> 
> The JHCTES program appears to conflict with what Marco said about the K
> Factor. I wanted to point out that the program is correct when it shows that
> the secondary voltage (spark length) increases and the K Factor decreases
> when the secondary windings are increased. This obviously can not be
> extended beyond a certain amount because the secondary voltage would go to
> infinity as the K Factor is decreased. For this reason I set a limit on the
> number of secondary turns for the program.

Without losses, and considering the lumped model only, the voltage gain
really goes to infinity if the secondary inductance goes to infinity.
The problem is that even in ideal lossless conditions, the change in 
geometry caused by a longer secondary causes k to decrease, and the
number of cycles required for the energy transfer goes also to infinity.
The tuning also becomes very critical when k drops below ~0.02. 
In practice, losses eat all the power when k is low.

A fact mentioned in Marco's paper is that starting from a perfectly 
tuned system operating at one of the modes that result in complete
energy transfer, it is possible to obtain some increase in the voltage 
gain by increasing the primary capacitance or by decreasing the
secondary capacitance, detuning the system. This goes to a certain
limit, 
but by readjusting k it's possible to obtain a bit more of gain. 
Your program would show this, but only if the system is not retuned
after 
the changes.
This is an useful technique if the coils can't be changed, and the 
coupling is very high, but if after the capacitances are changed
the coils are redesigned for the usual tuning, the voltage gain becomes 
even higher. In any circunstance, the absolute maximum is sqrt(C1/C2).

> To my knowledge no one has ever made the necessary tests to determine the
> increase in secondary volts when the K Factor is increased by reducing the
> clearance between the primary and secondary coils. These tests would be of
> interest to find out how the secondary voltage conforms with theory. In fact
> this would be important information because coilers change the pri/sec
> clearance by raising the secondary coil. How much secondary voltage are they
> loosing when they do this?

These things can be predicted by the current models. If k is decreased,
more time is required for the energy transfer, the losses eat more
of the input energy, and the tuning becomes more critical.
The loss question is the complex problem, because there are many sources
of loss, and the most important, the spark gap and streamers at the
terminal, are nonlinear and dependent on many factors.

Antonio Carlos M. de Queiroz