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Light Bulb Experiment (Followup)
Here's a "Light Bulb Experiment" and toroid-ground discharge update:
Previously, I had used various sizes and wattages of light bulbs placed
in series with the corona current path. These lights unexpectedly
"dimmed" when passing heavier toroid-ground discharge currents. Dave
Huffman and Robert Stephens theorized that these higher current
discharges were bypassing the filament path due to unseen arc-overs
between the lamp-base leads. And after a few more experiments, I
concurred, but had no direct proof.
I just tried a slightly different experiment using a 100 Watt tungsten
halogen lightbulb. This bulb is about 2" long x 1/4" diameter, with the
filament going the length of the bulb, and having a ceramic & metal
termination at each end. This particular construction prevents any
flashovers, forcing both the corona and ground surge currents to flow
through the filament. Because of the larger filament wattage, I was only
just barely able to light the bulb when running streamers to air through
the filament. However, once toroid-ground discharges began between the
free end of the lamp and a grounded wire 42" above, the filament began
to glow fairly brightly.
This helped confirm that the previously observed dimming associated with
Mazda-based lamps was indeed an artifact due to the heavy current arcing
around and bypassing the filament. I very carefully observed the average
brightness of the bulb under the heavy-discharge condition while running
the coil at maximum power. I then connected the same bulb to a variac
and an AC ammeter to estimate the average current necessary to light the
bulb to an equivalent degree. This level was reached at about 400 MA,
implying that the lamp was seeing an "average" current level of about
400 MA during the ground discharges (sort of like a hot-wire
ammeter...).
Further measurements with a storage scope showed that each
toroid-to-ground discharge removed virtually ALL of the energy in the
Primary/Secondary system in a very short time. There was no further
ringdown, or any other activity until the next "bang". Each discharge
occurred near the first peak of secondary voltage (i.e., during the
first energy transfer/"Bang"). Each high-current discharge actually
consisted of an exponentially damped 10-20 MHz current, with virtually
all of the energy being dissipated in about 1.5 uSec. At full power, the
primary gaps fire 3 to 4 times every half cycle, or between 360 and 480
PPS. For analysis purposes, an average rate of 420 PPS will be used.
Using 420 PPS, with each toroid-ground current surge lasting only 1.5
uSec, the total time "ON" time per second is about 420 x 1.5 uSec or 630
uSec, implying a duty cycle of only about 0.063%. The toroid-ground
current peaks which would have to flow to "average" 400 MA can now be
estimated: Isurge=(0.400)/(630x1e-6) or about 635 Amps(!). However,
since the actual current surges are exponentially decaying during each
1.5 uSec shot, the actual current peaks are probably significantly
greater than 1000 Amps(!).
This explains why these discharges look so mean and evil... they ARE!
As always, flames, brickbats, and snickering are always welcomed. <:?)
Safe (and rubber-booted) coilin' to ya!
-- Bert --