Re: TC Secondary Voltage vs Spark Length (was - 12 MV 100 years ago)

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

Original poster: "Dr. Resonance by way of Terry Fritz <teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>


I might add that potential difference, ie, voltage, is dependent on on the
circuit parameters, ie, inductance and capacitance ratios.

Increased break rate can make a spark longer but does not change the
potential.  The potential is determined by V pri x sqr (Ls/Lp).  In actual
testing the potential usually is in the 85-90% range of this value.

Example, if you take any coil, no matter how large or small, and charge the
cap through a hi-meg resistance so it fires once every 10 seconds, then you
can use a standard spark gap measurement method to find the peak potential.
Another method, which we employ a lot, is to use an ignitron so the firing
can be precisely triggered.  Our measurements using these methods are in
close alignment with standard DC peak potential measurements similar to
impulse generator measurements.

When the break rate increases more energy is pumped into the previous ionic
channel and the spark length increases dramatically --- but the voltage
stays the same, ie, no change.

Sometimes this method increases the capacitance very slightly and the coil
is retuned (usually only 1/4 turn on primary) to compensate for this.  These
two capacitances can be measured accurately and the frequency shift easily
calculated or measured.

In summary, the max. peak potential does not change with increased break
rate, only the spark length increases as the break rate increases.
Unfortunately, these long stringy sparks at high break rates are usually not
as exciting as the thicker, fatter sparks in the 120 to 480 bps range.

With high power machines you only need to use a break rate sufficient to
insure proper quenching (usually 2nd notch).  Excessive break rates don't
always give the best appearance.

If you want to measure accurate voltage then fire the circuit in single shot
modes.  If you want long sparks, then use a higher break rate.  Voltage vs.
spark length is not related to break rate.  There should be two parameters
measured independently, ie, voltage vs. spark length in pulsed mode, to
determine potential, and second, break rate vs. spark length, to spark
length.

Terry Fritz's antenna system also offer a nice method to determine potential
without retuning the system.  It can be scaled up as high as required simply
by moving the receiving antennas further back.

We have taken on other methods, using X-rays, but these are too dangerous to
use for common measurements.

Operating in the pulsed mode, potential is usually around 85-90% of the
measured standard peak spark gap charts, ie, 85-90% of Vpri x sqr (Ls/Lp).

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913

 > It appears that until you or Malcolm or some other coiler makes another TC
 > Voltage vs Spark Length graph all coilers are going to be stuck with the
 > graph in the Tesla Coil Construction Guide. The Tesla Coil Design Manual
 > also has graphs that could benefit from more test data from coilers. These
 > graphs will also have to do until some industrious coiler develops more
 > up-to-date graphs with the data you say is presently available.
 >
 > In my previous post I forgot to give the TC details for which the graph
was
 > designed. The Voltage vs Spark Length graph is for the typical classical
TC
 > operating at about 120 BPS. The spark length is a controlled spark length
 > and not the streamers that coilers normally use to rate their coils. It
 > should be noted that there are many other possible graphs of this type
 > depending on the parameters, such as break rates, etc. Some of these
graphs
 > are shown in the Tesla Coil Design Manual.
 >
 > It is interesting to note that the Voltage vs Spark Length graph can be
used
 > as a  "KVoltmeter".  Only the controlled spark length is required to
 > determine the secondary voltage of any typical Tesla coil. After you
measure
 > the controlled spark length the graph will tell you the secondary voltage,
 > the same information you would get from a KVoltmeter. You do not need to
 > know the power input, the coil size, the capacitor sizes, the type of
 > operating gap, TOROID SIZE, etc, etc, to determine the secondary voltage
of
 > your coil. For example if you reduce the input power to your TC and
measure
 > the spark length the graph will give you the new secondary voltage just
like
 > a KVoltmeter!
 >
 > John Couture