Re: Big Spark Induction Coil

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

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

Hi Antonio, Malcolm, Godfrey -

Tesla list wrote:
> 
> 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>
> 
> >... 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 probably don't get, in what sense "dependence on spark length":
thought, the equations, leading to optimal ("magic"-) values of k,
regarding sec-voltage, don't contain any spark-length parameters? (- But
probably only some misunderstanding on my part.)
> 
> 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.

Nice, you verified the same behavior. Of course I'm not shure, what's
happening with the spark at "microscale", meaning if it's
lighting/extinguishing every half-cycle of the f1 oscillation, which
might seem plausible. The "light from the spark" experiment looks very
promising for that reason. I wonder, if a carefully designed
jacobs-ladder experiment, zooming the spark on a corresponding photo
(and, of course, registering the BPS, as a time-reference), might reveal
the same info? My current JL-pic's are just too coarse, to see anything
more, than a certain blurr within the single 50Hz or 100Hz (BPS was not
recorded) spark-strikes.

> 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 noticed it as well (and the difference to the "sim"). 

> 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.

Obviously a resistor, as a replacement for a spark, is very primitive.
I've tried to add a DC voltage source, in series to the 150k resistor
with "sim" 24Ab, setting the DC voltage to 1kV - 1.2 - 1.5 - 2 - 10kV.
While the primary voltage beeing distorted "somehow", I'm not able to
reproduce the observed effect, by this means. I'm also not feeling very
comfortable, giving a physical interpretation to this voltage source.
May be, the current-depending spark resistance, as well as the
rectifying effect of the gap, should be included somehow. I'm aware of
spark model-examples with much higher complexity, but have not yet tried
to implement one in any of my "sims" (i.e. http://205.147.9.162/nl50.htm
, "Spark Gap Modelling" by Christophe Basso, Intusoft). 

BTW: it would be nice to have a comparable "static spark gap" building
block for Microsim 8/Schematics. Anybody on the list knows, if it could
be included in the trial-version, and able to program it? (The starting
complexity could probably be taken from the link above).
> 
> 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.
> 
I'd really like to see the "photos of storage scoped waveforms of a TC
connecting to grounded object", Malcolm mentioned. "Think" the strike of
a TC to a grounded object would afford a different simple spark model,
than Terry's successful simple "220k+5pF-per-foot" streamer model.
Looking at operation of my big coil "Black&White", I see, most of the
time, sparks, connecting to some grounded objects. And the SRSG kept
cool during the short runs (< 1 min), in contrast to the ASRSG (for more
see: http://datacomm.ch/k.schraner/index.htm ,"sparks"). The withdrawal
of the energy by means of the sparks, has a mayor impact on quenching
and energy loss. In order to evaluate such situations, a sec-spark-model
for connecting-sparks would be helpful - probably ;o).

Godfrey, your comment:
"When one subject begins to shine a dim light on another subject,
mathematicians call this "moonshine"." is very much "my taste": thank
you for citing the poetic expression. The potential is probably given,
between TC's and induction coils. And is also supported by Antonio:
<snip>
> 
> > 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

Thank you all
               Kurt