RE: NEW COIL FIRING!
Subject: RE: NEW COIL FIRING!
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sat, 28 Jan 1995 22:58:00 GMT
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> From: bhaley-at-shore-dot-net (Brendan Haley)
BH> The question is: the winding stops about 4 inches from the
BH> top of the pipe. There is one sweeping wind from the end of
BH> the tight winding up to the top, where the discharge terminal
BH> is. Does this spread out the capacitance along this long wind,
BH> and away from the terminal. I have noticed that there is corona
BH> all along this wind, and the sparks seem to get stronger near
BH> the tight winding.
RQ> The only problems you are having is that: your discharger is
RQ> mounted too high up off the top of the secondary winding; your
RQ> discharger is too small in diameter; or both.
BH> Not to harp on the subject, but why does the distance between the
BH> winding and the discharger matter: i.e. what physical phenomenon is
BH> occurring. Is it extra resistance from the wire, or capacitance?
BH> Normally I would envision the points as electrically equivalent,
BH> regardless of this length. I know I am wrong in assumming this,
BH> and I am curious as to why.
BH> Also, while I'm asking, what purpose does the discharger serve?
BH> A coil still produces the wireless power transmission without the
BH> capacitive hat.
Ok, ok, ok, I give up already! First of all the toriod is the classic,
and most effective, electrostatic shield. Tesla was the first person to
use this particular shape for this purpose during in the course of his
work in Colorado Springs. The toriod works much better than a sphere.
You never bothered to really tell us anything about your coil system,
or the type discharger you are using. You should be using a toriod
discharger, but it sounds more like you are using a sphere; it may
even be a sphere that is smaller in diameter than the secondary coil
winding itself (I am guessing due to the complete lack of supplied in-
formation). Regardless, since the toroid is perferred, and more people
nowadays are using them, I am going to go on as if we are talking
specificly about toriods. If that does not apply, then please provide
more information next time. We love to hear details about people's
coils, dischargers, capacitors, etc., so you would find it hard to
bore us with detailed descriptions.
Anyway as I was saying, one of the most important characteristics of
the discharger is to shield the top windings of the Tesla coil to
prevent arcing and corona off the top turns of the coil. In order for
a discharger to provide good electostatic shielding and protection it
must be; physically close to the top of the coil, and larger in dia-
meter than windings the discharger is protecting. This has nothing
to do with capacity, resistance, or inductance. This is a character-
istic of ELECTROSTATIC SHIELDING.
One of the unfortunate things about many modern coilers is their belief
that the ONLY function of the toriod is to shield the top turns of the
coil from corona and spark breakout, which is somewhat the opposite of
your misunderstanding. For yet another major advantage of the toriod
discharger in Tesla coil systems is that the toriod introduces ISO-
TROPIC CAPACITY to the top of the secondary coil.
ISOTROPIC CAPACITY lowers the frequency of the coil and increases the
base current. It aids in balancing the coil out into a more functional
"RLC circuit" as opposed to just a huge, open ended, inductance. This
has the effect of allowing greater VSWRs (Voltage Standing Wave Ratio)
in the coil. The toriod is therefore a key component in achieving truly
phenomenal performance. It is a experimental fact that toriods can be
enlarged to a very great degree to achieve higher and higher potentials.
The upper limit of this gain is the ability of the coiler to pump more
power into the secondary and the ability of the coil to withstand the
electrical stress without breaking down.
The isotropic capacity of a discharger varies with it's distance from
ground and other conductors. But this variation is not a significant
factor to the problem of arcing and corona from the top turns of the
secondary, which is simply a problem of electrostatic shielding.
As to your last comment that "A coil still produces the wireless
power transmission without the capacitive hat." I would agree, but
any coil without a proper discharger or capacitive hat will be
terribly inefficient, and this would be especially true if the coil
was designed or used to transmit power.
BH> And finally, could you explain the role of the spark gap. I've
BH> seen it described as providing "harmonically rich" current in
BH> order to cause the tank circuit to oscillate. That is both
BH> nebulous and suspicious sounding to me. Is the spark gap width
BH> important in the tuning, or is it fine merely sparking?
Well first off lets make a distinction which points toward the true
function of the gap in the Tesla Tank circuit; Tesla referred to the
gap more often as a "break" than as a "spark gap". Secondly, the
common air gap is really more of an "arc" gap than a "spark" gap,
given that the current that passes through the gap when it is firing
produces a healthy plasma channel. Regardless, the spark gap is
plain and simply a high voltage switch that allows the capacitor
to charge from the power supply, and then to discharge in a high
current pulse. The performance of the gap is what allows the Tesla
Tank circuit to develop peak powers in the kilowatts, even megawatts,
from common AC supply mains.
Think about that gap as like a "brain" that controls the operation
of the tank circuit. It allows a maximum voltage to develop on the
capacitor when it is open, then upon closing allows the capacitor
to suddenly discharge with a high current pulse thru the Tesla Tank
circuit. Once the energy of the pulse drops, the gap opens, which
allows the capacitor to recharge for the next cycle. It is switching
the capacitor back and forth from a "slow" charging mode where it is
supplied by the step up xfmr, to an oscillating mode where it is
suppling high peak powers into the rapidly oscillating, high current,
resonant Tesla Tank Circuit. By closing the gap down you allow that
gap to fire at a lower voltage, and you thereby reduce the peak power
of the pulse that develops. This allows you to control the power level
of operation and the amount of strain put on the capacitor. Another
factor to consider is the duration or "dwell" time of the arc in the
gap. The quicker the gap functions (switches open and close) the greater
the peak power developed, the more strain is placed on the capacitor
BH> Sorry to ask so many questions, but now that I finally got the
BH> thing working, somewhat, I am filled with curiosity. I was hesitant
BH> to ask these questions until I had a working coil, and now I feel
BH> more involved. So, any suggestions that would help me on my quest
BH> to becoming a better coil builder are greatly appreciated.
Well as this has grown in the last hour so into several pages I would
think that I have left you with some food for thought. I would really
appreciate it if you would take some time and let us have a short
paper with detailed specifications about your coil system.
BH> P.S. Thanks for the congratulations
Your very welcome! You earned it.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12