[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [TCML] Ambient Potential Polarity of TC - John F or Dave S has answer?
This question led to a number of experiments and the discovery of some
unrecognized (at the time) instrumentation artifacts from Keithley 600
series electrometers. The final answer depends on whether the Tesla coil
is actually generating corona or streamer discharges, terminal or
receiver breakout configuration, and in some cases, unique driver/coil
characteristics.
In 1996, Richard Hull did a number of measurements using an isolated
sphere, a HV cap or a Keithley series 610 electrometer, a medium spark
gap coil, and a low power (15W) Tesla Coil. The latter system used a
primary circuit that was switched by a hydrogen thyratron. This setup
generated a single unidirectional (half-sinusoid) current pulse of fixed
amplitude through the primary. This effectively "shock excited" the
secondary, causing it to ring with a relatively small, fixed amount of
energy - very repeatable. Classical primary ringdown and secondary
ringup was prematurely terminated since the thyratron only fired for the
first positive 1/2 cycle (at the primary frequency), then blocked
conduction in the reverse direction and thereafter until the grid was
triggered again.
Even though the energy transfered to the secondary was much too low to
cause breakout, Richard was able to consistently measure significant
charge transfer and negative DC voltages on an isolated sphere placed a
short distance from the TC when using the electrometer. Because the TC
power was so low, breakout (or even corona) did not develop, so corona
rectification was eliminated as a possible cause, and no other potential
mechanisms could be found for the phenomenon at the time.
In a medium power sparking coil, one can connect an isolated "receiving"
sphere to one end of a HV capacitor, the other end of the cap connected
to ground. When the TC is operated, the capacitor will (usually) tend to
accumulate a negative DC voltage. Corona rectification is the generally
accepted mechanism for this case, especially when one terminal
preferentially breaks out (non-uniform E-field). Corona occurs at a
lower voltage when the topload is negatively polarized, but streamers
tend to grow quicker when the topload is positively polarized. This
effect can be used to create a "corona rectifier". It is also possible
(by using a sharp point on the receiving sphere, or via unique coil and
driver configurations) to develop a positive voltage on the isolated
terminal/HV capacitor.
Some of these effects were initially reported by Richard Hull in July,
1996 in the TCML, followed by additional discussions in August, 1996.
Here are some of the more relevant postings:
http://www.pupman.com/listarchives/1996/july/msg00332.html
http://www.pupman.com/listarchives/1996/august/msg00589.html
http://www.pupman.com/listarchives/1996/august/msg00602.html
http://www.pupman.com/listarchives/2005/Dec/msg00820.html
The explanation for isolated sphere charging from the non-sparking low
power thyratron coil was finally resolved thanks to a number of careful
experiments conducted by Scott Fusare and Richard Hull several years later.
The apparent charging measured by the Keithley electrometer was actually
found to be caused by instrumentation artifacts from the solid state
front-end of the Keithley 600 series electrometers. Rectification could
occur in the presence of high dv/dt signals, thereby introducing a DC
offset that was not actually there.
By using other measurement techniques, it was determined that a
"non-sparking" TC does NOT induce a DC potential on an isolated
terminal. The complete report and conclusion can be found in Issue 35 of
the Electric Spacecraft Journal (December 16th, 2002). However, a TC
that causes air discharges (on either the topload or receiving terminal)
WILL tend to develop a DC potential on the receiving terminal. See:
http://www.electricspacecraft.com/hull%20for%20web.pdf
Bottom line:
Non-sparking coils should not induce a charge on an isolated receiving
terminal. And, although most sparking TC's will cause a negative voltage
to develop on the isolated terminal, the polarity can be reversed by
exchanging topload and receiver breakout roles, or by using certain
coil/driver techniques that preferentially promote positive topload
"burst corona" breakout. The latter effect has been demonstrated on
pancake coils during a number of experiments (not on TCML) privately
communicated to me by Jeff Behary. For most spark gap Tesla coils using
a topload with a breakout point, the voltage developed on the isolated
terminal is _usually_ of negative polarity.
Bert
--
*** /\ ******************************************************
__ _\/_ __ * * * * * * * * *
\_\/_/\_\/_/ We specialize in UNIQUE items! Coins shrunk using
/\_\/_/\ ultra-strong magnetic fields, Captured Lightning
_\/_/\_\/_ (Lichtenberg Figures), & technical Books. Please
/_/\_\/_/\_\ come visit us at http://www.capturedlightning.com
/\ * * * * * * * * *
*** \/ ******************************************************
futuret@xxxxxxx wrote:
I seem to remember that there was some controversy about the
polarity, and the original results were over-turned a couple of times
as various experimenters found differing results. An article was
published in Electric Spacecraft magazine, and then there were some
follow-up articles. I don't remember offhand what the final outcome
was. Maybe Bert Hickman or others have something to say about this
issue also? I think the question was eventually resolved.
John
-----Original Message----- From: Bert Pool <micro_wave@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> Sent: Sun, Jan 31,
2010 9:49 am Subject: Re: [TCML] Ambient Potential Polarity of TC -
John F or Dave S has answer?
As I recall, Richard Hull did some measurements with a Keithly
electrometer, and determined that there was a steady state field. We
know that positive and negative electrical discharges do NOT have
identical characteristics, and *might* lead to a net charge of one
polarity or the other. John Freau or Dave Sharpe, both who have
visited Hull's labs back in the day, might be able to confirm this
with more detail. Guys?
Bert Pool
stork3264@xxxxxxxxxxx wrote:
Assuming a simple quarter wave Tesla coil referenced to ground is
there a measurable electrostatic field potential of the ambient
space surrounding the top load? Without doubt, potential is
varying between positive and negative with respect to ground. The
question is there a measurable ES field of a single polarity? Is
there favoring of positive or negative plasma discharge in air? Is
there an inherent rectification of the plasma? For safety of our
equipment measurements are usually AC. Has anyone performed a DC
measurement of the ambient potential field referenced to ground?
Stork
_______________________________________________ Tesla mailing list
Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________ Tesla mailing list
Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________ Tesla mailing list
Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla