Re: Big Spark Induction Coil

["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: "Kurt Schraner by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <k.schraner-at-datacomm.ch>

> Well, even in the "sim", when displaying the secondary voltage (accross
> the sparkgap), at first, we observe a very high peak (i.e. 16kV for test
> 24A), and then essentially low voltage accross the spark, till the high
> f1 oscillation has ceased, when the f2 oscillation appears. This leads
> to the second part of your posting: The tuning of the coil, including
> primary and secondary LC's, as well as coupling, can be implemented to
> probably optimal values, just for creating the first energy transfer
> from prim' to sec' -and highest voltage- BEFORE secondary spark
> breakdown. Did I get you about right?

Yes. The adjustments would depend on the spark length.

I made some experiments with an ignition coil today, and was able to
reproduce exactly the same behaviors. When the primary circuit opens,
the input voltage rises first, then the secondary voltage rises to
a high value. The start of the
spark decreases the secondary voltage to a low value, and causes a
sudden drop in the primary voltage. After this, the f1 oscillation
is visible in the primary, for a few ms. When it ceases, the f2 
oscillation begins. The f1 oscillation really appears to correspond
to the duration of the spark. I will try another experiment to
confirm this, looking at the light from the spark.
I noticed also another strange thing, that also appears in your
oscilloscope images: The f1 oscillation doesn't converge to the
supply voltage, but to a different value. The f2 oscillations
converge to the supply voltage. I interpret the cause of this as
a constant voltage drop at the spark being reflected to the primary,
while a current with a significant DC component flows through the 
secondary for some time, expending the energy stored in the coil.
This doesn't appear in your simulations, because your "spark" is
a linear resistor. Replace it by a voltage source and the offset
will appear in the simulations too.

Are experimental waveforms for a Tesla coil, showing the primary
voltage while a spark to a grounded object occurs at the secondary, 
available somewhere? The same kind of behavior is to be expected,
specially in a coil with a small terminal, and a short spark.

> There's just a 3rd thing, which also triggers my interest: the
> capacitive loading of the secondary, without generating sparks. As
> ,essentially, a "capacitive shorting" of the secondary, it produces
> comparable first f1 ringings similar to a spark (see i.e.test 33A). But
> it's as well forming the L2C2 resonant circuit, and as such, makes the
> system behaving differently than with spark. The observed frequencies f1
> and f2 concur with those fI and fII calculated from A.Bowers's idealized
> induction coil theory, while, with a non-capacitively loaded, but
> sparking coil, this is not generally the case. I'm yet pondering about
> it...

My experiments show the same. It is the same double oscillation 
characteristic of a Tesla coil, or two coupled LC tanks. As the
coupling is high, the two frequencies are widely separated, and
their decay time is also very different. 

> P.S. I'm afraid, Terry must stop this thread, getting too much off
> topic?

An induction coil, besides being a classical form of power supply
for a Tesla coil, is mathematically very similar to a Tesla coil.

Antonio Carlos M. de Queiroz