Greetings-
Single resonance still holds an appeal for me--in part since Tesla
himself, with the benefit of solid-state technology, would surely have
favored it. He didn't, after all, want sparks: he wanted to transmit
power, not into wasteful sparks but out to the populace at large.
Cockamamie idea, of course, and he and his investors lost a bundle, but
he was still a genius.
So here's what I'm working on--after some years' hiatus. To produce
sparks, of course, not radiate power.
Based upon my original notion, which worked but in hardware I made
hopelessly complicated: 8, 1000 uF/450V capacitors arrayed together
with 8 power MOSFETs in a ~12" diameter "ring" arrangement incorporating
the equivalent of a 6-turn primary coil. The capacitors to be charged
to full-wave-rectified and doubled mains voltage. This I've built and,
driving it temporarily with 2 signal generators (to provide for
pulse-bursts) and so far only at ~40 V charge, I find that it appears to
work as simulated. The scheme is for the MOSFETs to connect 4 of the
capacitors in series with the coil during each 1/2 cycle, at the
secondary's Fr. That yields, in simulation, ~240A p-p primary current
at full capacitor voltage of ~300. I've devised also a simple
constant-current capacitor-charge circuit so that I won't pop a circuit
breaker trying to charge 8000 uF (plus another 2000 for the doubler)
right off the mains from a cold start.
The 12" x ~39" secondary coil I'll use is left over from my prior
attempts, along with its 6 x 24" Landergren toroid. I have another,
taller, coil as well.
But in simulation I also found much that I wish I'd found out before:
1. All capacitors may be charged directly in parallel, with the
inclusion only of a single 10 mH isolation inductor between the groups
of 4. 2. All MOSFET sources may be (and are) tied together. 3. Each
4 drains may be (and are) tied together. And 4. All 8 MOSFETs may be
(and are) driven from a single (D44H8/D45H8 H-bridge) source. I've
built the H-bridge and it seems to do the job. Now I have to build the
l.v. signal-processing part, which takes secondary-return current and
amplifies and gates it to provide the MOSFET drive. I've so far
simulated that successfully; it requires only 3-4 CMOS DIP ICs + the
usual small parts--plus a l.v. power supply, of course, which I also
have left-over.
So circumstances allowing (I'm 85), I'll be making sparks again before
too long. Since I won't use a breakout-point, the sparks very
charmingly will dance all around the toroid (as they did before at
20/second or so), making lots of noise and ozone.
Ken Herrick
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