[Prev][Next][Index][Thread]

Re: NSTs and Cap charging tests (Static gap-Sync vs. Chaotic BPS)

Hi John, Richie, Malcome, Gary, Terry, Reinhard, Dr. R., and all others
following this thread.....Although I'm a rank amature at TCs compared to
you guys, I thought I would share the results from some testing I've
done over the last three days on 'Reddy Kilovolt' , my 8" x 34" coil
with 15,000 volt/150 mA NSTs, 26.77 nF tank cap. , and a Gary Lau style
single static gap with vacuum airflow quenching/cooling. The NSTs and
caps were selected to resonate at 60 Hz, or thereabouts. During these
tests, only the gap spacing and input voltage were changed; everything
else remained as above.....As stated in my last post, with a gap spacing
of about .375", when input voltage reaches about 100 Volts, the input
current drops sharply, from 30-35 Amps to 16-18 Amps, and the sound of
the gap and sparks changed from a raspy noise to a steady,  pleasing
tone. Spark output also decreased slightly. This sounded to me like the
gap was firing in sync with the line, so I tried the following to
confirm this. (If anyone sees a flaw in these tests, please say so, as
I'm here to learn). First, I set up the O-scope (single trace) about 20
feet from the coil, and attached a short length of wire to the probe. I
then adjusted the vertical amp and horizontal sweep rate (in the 'free
run' mode) to display two complete sine waves from the 60 Hz background
'hum'. When the coil was fired, the initial bang from each discharge
would show up superimposed on the 60 Hz sine waves as a vertical spike,
followed by the ringdown envelope. Sure enough, when the NSTs were
drawing the least current, and the noise of the gap and sparks became a
steady tone, the gap was firing in perfect syncronization with each 1/2
cycle of the line. Each bang occured at EXACTLY the same place on the 60
Hz waveform, just a few degrees before each voltage peak. I was amazed
to see the gap firing with such regularity, as there was absolutly no
jitter at the firing point on each 1/2 cycle. ('Scope triggering turned
off and set to 'free run'). Note: gap is two 1-1/4" copper endcaps with
3/8" holes in the center for vacuum airflow. Gaps were cleaned before
tests were done. After running the coil for a few minutes, oxide starts
to appear, and firing starts to become erratic in the sync (120 BPS)
mode. Finaly, when enough oxide builds up, this sync mode completly
stops, and chaotic firing prevails , although this dosen't seem to
decrease spark length untill oxide gets heavy enough to cause the safety
gaps to fire. If input voltage is either raised or lowered, chaotic
firing starts, current draw about doubles, and spark length increases
slightly. Raising the input voltage past 100 Volts to 120~140 Volts ,
sparks grow rapidly in length, up to 6 foot, although input current
rises to 35-40 Amps. As one would expect, decreasing the gap spacing
lowers the voltage where the 120 BPS line sync occurs to about 60 Volts
input. At this spacing at 120 Volts, the gap was firing twice during
each half cycle (240 BPS) once just before and once just after the
voltage peak, although spark output was WAY down to <1 foot, even with a
breakout placed on the toroid. Widening the gap increases the spark
length up to the point where the cap can no longer charge and fire the
gap at least once per half cycle (about 7/16"). Best performance for
this coil is about 3/8" or .375"~400" gap
spacing...................................... Conclusions???
(Semi-uneducated guesses, really) Single static gaps can fire at
precisely every half cycle and within a few degrees before the voltage
peak, at least for my 60 Hz resonate NSTs / Cap combo.....With proper
gap spacing and charging current, the gap can fire multiple times per
half cycle.....When not firing at 120 BPS or some multiple, firing
becomes chaotic.....Chaotic firing=higher current draw=lower power
factor=lower efficency, but=longer sparks.....Sync firing=lower current
draw=closer to unity (higher power factor)=higher effiency, but=shorter
sparks.....Oxide on copper gaps greatly affects the firing voltage and
sync stability.....Best efficency (highest power factor) occurs at 120
BPS.................Like I said, these are only observations and
guesses; All coments welcome, as well as corrections! SAFE
SPARKIN'...T-coiler Howdys from Texas...........  Tony Greer