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Well I'm proud to announce that I have acheived first light on my MOT
powered 4" budget coil. Actual first light was a few nights ago but I wanted to
do some more experimenting before officially announcing it. Maximum spark
length the night I fired it up first was about four feet. Last Night with a bit
more tinkering resulted in the coil consistently hitting 54 inches.
Testing was done in my driveway at about 1800 VA input. The coil consists
of 2 MOTs wired in series for about 4800 volts (just over 6000 volts -at- max
variac setting), an MMC consisting of 27 (3x9) 330nf 2kvdc snubbers for a total
of 110nf -at- 18kvdc. The spark gap is two peices of 1/4" brass threaded rod blown
by a 40 psi air compressor. The secondary is 4 3/16" od x 23 some odd inches
wound with #28 magnet wire. Primary is 1/4" Cu tubing w/ 1/4" spacing 6.25" id
tapped -at- turn 6.2.
Topload is 4.2" x 17" corrugated Al dryer duct. The budget part is that the
coil only cost about $90.
The interesting thing about the coil is that when the spark gap power arcs,
(it does this after about one minute) the sparks don't get shorter, but
coallesce (spelling?) into one big thick spark that readches out and up with
huge branches coming off the main section of the spark. This spark is very
frantic in the way it jerks about the toroid, and lasts until I either turn
down the variac or it trips the 15 amp breaker (about 20 seconds).
I can't wait until later this week when I can get a bigger breaker and a
bigger (read 8" x 30") topload.
Open to questions or praise!