First high Power session since '99

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

Original poster: "Dave Hartwick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>

Last night, I fired for the first time my new 4" secondary with my 5 kVA
14.4 kV Piglet.

Secondary: 4.25" x 24", 1500 turns #26
Toploads: 6" Slinky toriod, topped by large coffee can, topped by 13" Slinky
toroid, topped by
          5" x 28" drain pipe toroid
Primary: 11 turn, 1/2" Cu tube Pancake, max 75 uH
Caps: 2 - Condenser Products 0.05 ufd, 20 kVAC in series "Equidrive" for
0.025 ufd total
Gap: single AirBlast type, Cu electrodes.
Ballast: 1 MOT in each 240 leg, 240 VAC, 28 AMP Powerstat Variac
Fo: ~140 kHz, K: <0.9


I was running this system with no protection or EMI filtering--probably the
last time I'll do so. I ran around the house and unplugged the delicate
stuff. The gap is across the xfmr, and everything was far enough away from
the topload that strikes weren't an issue.

Anyway,  last night I initially started to piece together an MOT voltage
doubler supply. First I was going to use the standard 2 MOT arrangement,
then said "What the heck, I'll use 3 transformers". Then, realizing I have
about 2 dozen MOTs, I decided to go with 4 in series, no doubling. Well, by
that time, I figured I may as well dust off the heavy firepower--Piglet
time.

You see, I had been firing with 2 15/30 NSTs, but I was starting to tire of
the wimpiness, so when one of the NSTs developed a weak side, I thought
about MOT supplies, and the rest is history.

This system is very well behaved. No racing arcs at power levels that were
tripping the 40 amp 240 breakers. One possible reason: The elevation and
configuration of topload. While constructing the secondary, I purposely left
6" of the top of the PVC form extending above the close turns to provide
sufficient room for adequate spaced wind-out, and to elevate the toploads.
The small slinky toroid seems to provide electrostatic shielding at the
immediate top of the secondary. Also, K <0.9 may be high. This particular
primary was designed for 6" systems.
The ID is 10-11". I clearly was not overdriving the secondary.


I'm firing in the basement---quarters are tight (until I move the table
saw). I must carefully move TV cable runs around, install metal screen to
the ceiling in potentially vulnerable areas, tie nearby fluorescent lights
to RF ground, etc. This meant that the large top toroid major diameter was
only about 30" from the nearest grounded object, in this case a steel
vertical support column imbedded in the concrete.

Thus, I obviously cannot report maximum spark length since it was clearly
limited; but I can report that the arcs to that steel column were the most
intense and energetic I've ever seen in my Lab. Not quite pure white, but
almost there. Just a hint of blue.

Runs were lengthy and numerous. I took time to carefully study the nature of
the arcs. Each single arc actually consisted of ~3-4 thinner arcs very
closely spaced and dancing around each other. I don't think I've observed
this before. The path traced was highly convoluted, like a writhing snake,
with many partial loops, curves and turns. It was fascinating. I brought a
neighbor kid over who likes this kind of thing and he was enthralled. (Wish
my wife, who was at her sister's, was similarly interested!)

And the smell. Higher power levels clearly produce an acrid odor that is
quite different from that produced at lower power levels. Must be compounds
of Nitrogen. Only now, almost 24 hours later, has the smell which permeated
the entire house dissipated.

The weakness in this system--shockingly(!)--must be the gap. I was running
5/8" to 3/4" between 'trodes. This particular gaps is powered by a unit from
a massive Oreck Shop vac, and truly moves the air both through the hollow Cu
electrodes and perpendicularly across and through the gap. The
characteristic green color as the Cu vaporizes and conducts (plasma) can be
seen in the blinding arc, in front of which I've mounted a piece of welding
glass for safe observation. Surely those Cu gaps do not help the quench.
They are not just pitted, but partially melted and charred away like the top
of an old volcano.

I'm think that moving that air through a TCBOR style multi-static gap may
work better. Not just for cooling, but confined with a plenum and forced
through only the gaps. The need for a solid rotary is nagging me. I wonder
how Rich Hull's series quenched rotary type would work? A primary  optimized
for this secondary must be built, but I will NOT use 1/2" tubing--very
difficult to work with. Better toroids are needed. The Al foil on the big
one is a shredded mess.

Anyway--A very good session. I didn't blow the CP caps, which are
theoretically limited to 120 BPS. I must encase them in case of explosive
failure.
Dave H