[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [TCML] Telsa coils + capacitor bank = ?
Hi All,
Aaron wrote:
I 99% sure Bill Wysock and/or Dr. R. did a similar experiment years ago.
Perhaps one of those folks will chime in?
Cheers,
Aaron, N7OE
GL: Not sure who else has performed this misdeed, but I originally
tried it in Graz, Austria in 1992, then once again in Austin TX in 1997:
http://www.lod.org/Projects/120L50K/austin01.jpg
Lots of fun, but no decent instrumentation in either case!
Now we're trying to resurrect some old dusty HV equipment, and attempt
to more carefully characterize how initial conditions affect the runaway
current development.
Bert wrote:
[snip]
>> Josh Bailey wrote:
> Here are two series' of photos (frames from an MJPEG capture
running at about 30 fps):
>
> http://vandervecken.com/images/capbanktest1/
> http://vandervecken.com/images/capbanktest2/
>
> Q1. What conditions must exist for the capacitor bank to
> discharge? We noticed that sometimes the graphite was struck
> multiple times before it discharged. We also noticed that
> sometimes the bank was not fully discharged (still had 3-4kV on it).
>> In general, the brightness of a spark is a proportional to the
amount of current passing through it. The base of air discharges from a
Tesla Coil (TC) is the brightest and hottest part since the sum of all
the branching discharge currents pass through the main channel. As you
move away from the terminal, the discharges begin branching, with each
branch carrying a portion of the total current. As the current flowing
through more distant branches becomes progressively lower, the channel
diameters become smaller, and the discharges become more purplish and
dimmer. The tips of the discharges transition to a bluish glow (the
streamer-corona region) where the gas temperature is barely above room
temperature.
>> Unconstrained sparks and arcs in air have a negative resistance
characteristic: the more current you force through them, the hotter
their cores become, and the lower their electrical resistance. Because
the more distant channels are cooler and smaller in diameter, these
remote channels are considerably poorer electrical conductors.
>> When a Tesla Coil is operating near the limit of its spark length,
you may see sparks sporadically/weakly connect the TC terminal to ground
without the characteristic brightening that we usually associate with TC
ground strikes. In this case, although the spark has indeed bridged the
gap, the combination of high resistance from the discharge path, and the
fact that we are close to being max'ed out on TC terminal voltage,
prevents any major increases in channel current - even though we've
actually bridged the gap.
GL: Thanks for the great description, Bert. The early misfires make
more sense now. I have a tendency to view any visible electrical
discharge as a wire at these voltages, but your point is now obvious
that the tendrils of the arc must be presenting relatively high
resistance if the TC terminal voltage is maxed out, as in the case of a
barely bridging arc. Clearly the relatively low energy storage bank
voltage won't do so much in such a case.
[snip]
>> During each oscillation, the arc current passes through zero,
temporarily extinguishing the arc. Usually it is quickly reignited by
the high voltage from the capacitor bank. As the energy in the system
decreases, so does the arc current, causing the arc resistance and
overall arc voltage drop to rise. The voltage drop across the arc is
also proportional to its length. As the bank energy decreases, a point
is eventually reached where the arc can no longer be reignited, and the
arc goes out for good.
>> Once the arc finally extinguishes, residual energy will still be
left in the capacitor bank. This is typical behavior for an LC and spark
gap system. Because of the relatively long arc involved in Greg's
system, the stranded bank voltage is proportionally higher. You may also
see significant variation in residual bank voltage if the Tesla coil
continued to operate during the bank discharging process, since it would
assist in reigniting the arc channel.
GL: Makes sense. The rather slow [70Hz] resonant frequency of the
secondary and energy storage bank might also be assisting the ion
recombination?
>> Bert
--
***************************************************
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, Lichtenberg Figures (our "Captured
Lightning") and out of print technical Books. Visit
Stoneridge Engineering at http://www.teslamania.com
***************************************************
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla