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Re: Arc Impedance Study - Computer Models



to: Terry

Nice post with clean, clear data.  Your 1" sec elevation is very close to
my usual recommendations of 1 to 1 1/2 inches above the plane of the pri
coil for bottom turn of sec coil.  Any coiler running a 20 to 24 inch dia
coil will find 7 to 9 inch elevation of sec coil above the primary plane
works best.

Malcolm also recently posted some confusion regarding, "the resonator
behaves as a lumped circuit exhibiting a uniform current throughout its
windings and wondered how the current could be the same at both the top and
bottom with no topload?"  The answer is --- it isn't the same.  Without a
large topload their is distributed not lumped capacitance throughout the
length of the sec coil and due to this distributed capacitance the coil
acts more like a transmission line.  The sec coil will support a variety of
harmonics (some quite strong).  When a large lumped capacitance is added to
the top the harmonics are supressed and the sec does not have even current
at both top and bottom.

Once corona ruptures the air the sec coil becomes de-tuned and its Q factor
quickly lowers.  An equilibrium is established when the spark load and
internal secondary losses are equal to the power being transferred from the
primary.  When the primary power level becomes less than the sec spark load
plus internal secondary losses, the primary starts to run out of power
power and rings down -- hence quenching can occur.  As long as pri power is
greater than sec power during the transfer process, then spark gap
(primary) quenching will not occur.  

Ringup is uniform with even volts/turn across the sec inductor with a large
topload.  

Malcolm also discussed the VSWR vs. Q factor (1.3 x full ring-up value). 
The term VSWR does apply to transmission line coils with little or small
topload, however, VSWR is not relavent to modern design with large topload
capacitive values.  VSWR is a transmission line term and is not important
with large toploads.  An interesting overlapping "gray" area does exist
with systems operating with a medium size topload --- that is somewhere
between small topload and large topload.  This "gray" area is somewhat of a
balance between these two processes and explains clearly why some
investigators are obtaining strange results in their measurements.  These
measured values like Lou Balint is obtaining will not apply to resonators
and magnifiers with large top loads such as Rich Hull and TCBOR have
constructed.  Lou's work would apply more to small systems without large
toploads and may give false impressions if this data is applied to a
spark-excited system with large toploads.  Caution is advised in this area
of interpretation.

For what it's worth,  . . . . .

DR.RESONANCE-at-next-wave-dot-net



----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Arc Impedance Study - Computer Models
> Date: Saturday, October 10, 1998 5:01 PM
> 
> Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
> 
> Hi All,
> 
> 	I ran a bunch of Spice models today using an arc load of 220k ohms and
> 5pF.  This is the estimated arc load value I found from measurements on
my
> coil.  I tested the ability of the coil to deliver power to the 220k
> resistor while I varied the coupling, Lp, the ratio of Ls and Ct, and Fo.
> 
> The numbers my computer model used are as follows:
> 
> Primary Capacitor Voltage	20000
> Primary Capacitance		17.05uF
> Primary Resistance		3 ohms
> Primary Inductance		120.6uH
> Fo					111.0kHz
> Secondary Inductance		75.4mH
> Secondary Total Resistance	270 ohms
> Secondary Capacitance		27.26pF
> Secondary Load			220k ohms + 5pF
> 
> 
> 	First the coupling tests.  I tried a number of coupling coefficients and
> found the following:
> 
> K		Peak Current	Burst Time	Relative Power
> 0.05 		336mA			120uS		2.98
> 0.105		597			80		6.27
> 0.123		653			70		6.56
> 0.145		719			63		7.17
> 0.172		783			55		7.42
> 0.201		846			45		7.08
> 0.250		909			35		6.36
> 0.300		966			31		6.36
> 
> Relative power is calculated by taking 220000 ohms multiplied by the peak
> current squared and then multiplying by the burst Time.  This gives an
> estimate of how much relative power is being dissipated in the 220k ohm
> resistance.  this should be an indicator of the power being delivered to
> the arc.
> 
> It appears that a coupling of 0.172 is best for my coil.  This
corresponds
> to my secondary being 1 inch above my primary.  This has consistently
been
> the best point for my coil and now these calculations show this also.
> 
> 
> 
> The Primary Inductance may have to be somewhat greater than the
calculated
> value due to the added terminal capacitance from the streamer.  Richard
> Hull and others tune their coils with about 5% greater primary inductance
> to account for this.  My results are as follows:
> 
> Inductance	Peak Current	Burst Time	Relative Power
> -20%		588			40		3.04
> -15%		635			45		3.99
> -10%		667			52		5.09
> -5%		698			56		6.00
> 0%		719			63		7.17
> +5%		737			65		7.77
> +10%		739			65		7.81
> +15%		734			69		8.17
> +20%		718			66		7.48
> 
> The primary inductor appears to have to be 15% greater than the
calculated
> value for my coil.  This allows for the added 5pF from the streamers. 
The
> range of +5% to +15% seems to be relatively constant and supports my
coil's
> insensitivity to exact primary tuning.  These results support what many
> have reported.
> 
> 
> Ls to Ct ratio.  There has been much discussion on what effect the ratio
of
> secondary inductance to capacitance my have on coil performance.  In
effect
> this is sort of a measure of the output impedance for a coil.  
> 	For this test the frequency is held constant.  The secondary inductance
is
> varied and the secondary terminal capacitance is adjusted to keep the
> frequency consistent.
> 
> Inductance %	Peak Current	Burst Time	Relative Power
> 200%			747			57		6.99
> 150			741			60		7.25
> 100			719			63		7.17
> 66.7			664			65		6.30
> 50			608			65		5.29	
> 
> The burst time is very hard to see in the first two tests which make the
> results rather hard to use.  However it appears that a somewhat larger
> secondary inductance would provide more power to the arc.  It appears,
> however, that the Ls to Ct ratio is not having all that great of an
effect
> on the output arcs.
> 
> 
> 
> Fo.  In this test, I proportionally scaled all the primary and secondary
> capacitances and inductances to see what difference changing Fo would
have:
> 
> Fo		Peak Current	Burst Time	Relative Power
> 27.75kHz	321			245		5.55
> 55.5		533			124		7.75
> 111		719			63		7.17
> 222		777			35		4.65
> 444		741			20		2.42
> 
> When I vary the primary capacitance, the primary energy changes so I need
> to account for this by dividing the Relative Power by the relative
primary
> cap size: 
> 
> Fo			New Relative Power
> 27.75kHz		1.39
> 55.5			3.86
> 111			7.17
> 222			9.3
> 444			9.68
> 
> So this indicates for a given primary energy, higher frequencies are more
> efficient.  These last results may be affected by the size of the arcs
such
> coils would produce and the resulting different loads those arcs would
> have.  Apparently this is due to the fact that higher frequencies produce
> lower reactance in the 5pF load capacitance and thus allow more current
to
> flow.  Of course, high frequency coils don't have nearly as much primary
> energy as large coils so larger coils, that have proportionally more
> primary energy, do somewhat better.
> 
> So what does all this mean?  For my coil I should set the coupling up to
> 0.172 and tap the primary 15% higher.  Perhaps running the experiment
over
> trying high secondary terminal capacitance would also show some
interesting
> results.  This would lower the system frequency without hurting any other
> factors.
> 
> ----
> I just went back and did this with the following results:
> 
> Ct,Lp Ratio		Peak Current	Burst Time	Relative Power
> x4			316			125		2.75
> x2			512			88		5.07
> x1			719			63		7.17
> /2			872			45		7.53
> /4			926			35		6.60
> 
> This would indicate lowing the secondary terminal capacitance would
improve
> power to the arc.
> ----
> 
> 
> 	In general this spice computer test shows that the results from the
> computer model match the scope results well.  The scope photos and the
> spice models are the same.  Best yet, the spice models appear to be
> accurate enough to test coil designs on the computer and have those
results
> match real world observations.  In short.. It all works :-)
> 	There is still some refining to do but the use of 220k ohms plus 1pF of
> capacitance as a value for arc impedance seems to be holding up so far.
> 
> 	Terry Fritz 
> 
>