I'm gathering materials and plans to perform this experiment -
determining
the cap size that will extract maximum power from an NST, at 120 and
140VAC
input. The power indication will be via monitoring the surface
temperature
of the halogen lamp dummy load that replaces the primary coil. I plan to
test a 15/60 NST, and two 15/30 NST's, all unmodified.
I'm having a hard time figuring out how to fasten a thermocouple to the
quartz lamp tube. I want the connection to be robust, as there will be
considerable thrash as I change NST's and cap sizes, and I don't want
lamp/thermocouple coupling to vary.
Obviously I'll clamp down the thermocouple wire to the base of the lamp
assembly (http://drop.io/garylau), but could use guidance on the business
end. I thought about just wrapping many turns of 30 gauge copper wire
around the thermocouple wire and quartz tube, but worry that the
quartz and
copper will have differing expansion rates and might damage the tube. I
have high-temperature polyamide (kapton) tape that I can wrap the
thermocouple to the tube - not sure how that will fare with the heat. If
nothing easy presents itself, I guess I'll fashion a spring clamp to
apply
gentle pressure to the thermocouple tip and tube.
Any thought on this problem or the experiment design would be welcome.
Also, I can't seem to locate the table that relates NST size and gap
type to
suggested cap size. It had been on hot-streamer and mirror sites, but I
can't seem to locate it.
Regards, Gary Lau
MA, USA
On Sun, Jul 25, 2010 at 7:40 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
I just thought of another use for the halogen lamp dummy load. When one
begins the design of a coil, after you decide what size NST you'll be
using,
the next step is to determine the tank capacitor size. The standard
method
is to just look it up in a table for what size your NST is, using an
LTR cap
for a static gap, being some factor 1.3-1.7 times the mains-resonant
value.
Personally, I've found better results using ~2 times the mains-resonant
value.
Experimentally trying different cap sizes isn't practical, as each
time you
change the cap size, you must also change the secondary to keep
things in
tune (which changes multiple things, rather than just one), and you must
also subjectively judge at what point the sparks are better, at widely
distant points in time.
However, if you replace the primary with the dummy load, one can quickly
change the cap size and nothing else, and gauge the amount of power
processed by the brightness of the lamps. For a more quantitative
result,
you can mount a thermocouple on the lamp and see with what capacitor
size
causes the lamps to get the hottest. I believe that this would give a
very
accurate determination of the optimum capacitor size. I'll have to
resurrect my coil and try this!
I've also long suspected that the optimum cap size might differ
significantly depending upon the applied AC voltage to the NST -
potentially
very different for 120 vs. 140VAC. It would be easy to determine if
this is
true using a dummy load.
Regards, Gary Lau
MA, USA
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