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Original poster: "Kennan C Herrick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <kcha1-at-juno-dot-com>
Finally I have .jpg images of my s.s. coil & am posting them to
as KCH_tcg1.jpg and KCH_tcg2.jpg.
Tcg2 is a bit of tongue-in-cheek (and thanks, ol' Nic, for your
inspirational photo) but here's a bit (repeating somewhat from prior
postings) about tcg1, "Herrick's Patented Solid-State Alternating-Current
Thunder and Lightning Entertainment Machine":
1. Input, 117 VAC, 60 Hz, 0-1800 W.
2. Physical size, 2 ft. square x 5 ft. tall.
3. Primary design:
3.1 Two equivalent untuned electrical turns driven by power MOSFETs.
3.2 Present configuration, 24 pairs of 500 V, 85 A MOSFETs in a patented
circuit (U.S. #6,069,413 which can be viewed at
http://www.patents.ibm-dot-com/ ) delivering ~200 A current-bursts through
the 2 equivalent primary turns. It can be more fully configured, with 36
pairs, to deliver ~300 A. There are 6 pairs of MOSFETs plus associated
energy-storage capacitors per (horizontal) printed circuit board. With
each such board is associated an additional (vertical) circuit board
holding the MOSFET drivers and an off-line switching-current-source to
both charge the capacitors and keep mains current limited to a selected
maximum. Attempting to charge some 43,000 uF to 160V by merely throwing
a switch is guaranteeing instant trouble every time.
4. Secondary design:
4.1 12.5" coil diameter x 36" height.
4.2 Twenty ga. wire space-wound. Q = 80-100 -at- ~140 KHz resonance with the
toroid in place. Construction is: sonotube with Jasco Water-sealant II
applied; then closely-wound with .06"-dia cotton twine; then .003"
"Mil-grade" teflon over that; then the wire, wound in the groove formed
by the twine; then 8 beads of "Q-dope" to hold the wire in place.
4.3 Toroid, 6" x 24" Landergren.
5.1 Highest voltage to ground ever present anywhere in the primary
circuit, 160 V. Highest MOSFET turn-off transient, n.g.t. ~400 V.
5.2 Self-tuned: Secondary is the sole resonant element in a feedback
oscillator incorporating the power MOSFETs. Always dynamically tuned.
5.3 Spark rate continuously variable from 1 per button-press to 20/sec or
more depending on power-line current capability and spark duration.
5.4 Controlled via a small "wand" at the end of a 15 ft. cable. Wand
incorporates a collapsible ground rod for optionally inducing sparks.
5.5 Spark length, ~3 ft.
5.6 Spark duration, ~7 ms, fully-on and also ~7 ms interrupted -at- 64
cycles on, 64 cycles off, etc. Approx. 200 us secondary-voltage rise time
to commencement of spark.
6. Dissemination of plans:
6.1 I plan to offer my construction plans for a few tens of dollars fee.
They comprise 7, 11" x 17" drawings and a 16-page description. Anyone
interested, please contact me off-List. Although my primary scheme is
U.S.-patented (as part of my "entertainment"), anyone in the U.S. may
make 1 or more if not sold in commerce (and anyone else may, of course,
make dozens and sell them for thousands...if they wish).
In the tcg1 photo,
1. A 4x5 view camera was used with ASA ~60 film. A normal tungsten-lit
exposure with the coil off was followed by a 6-8 second time exposure
with no light except for that of the sparks (and the same procedure was
used for tcg2; first me & the coil, then the coil & the sparks).
2. The secondary just sits on the primary's wire-bundle, which is merely
18 ga. 2-conductor "speaker" wire and is formed to the ~12" diameter. It
is held in place with the 4 nylon-Velcro straps and a small centering
disk affixed to its bottom cover. It connects via a short cable with RCA
plugs to the red box.
3. All the MOSFETs stand upright and each has on it a copper-pipe
4. All the circuit boards are designed so that 6 pairs may be arrayed
within the 24" x 24" baseplate's "footprint". I currently use 4 pairs.
5. The big inductors (4 are currently used) are for the switching
6. All the 5V electronics (some 9 garden-variety ICs, a few
opto-isolators, associated components, etc.), the low-voltage power
supplies and the single mains bridge rectifier for the 160V are within
the red box.
7. The rotary switch allows for monitoring of various voltages & signals
via a BNC connector.
As I've commented upon already, I believe that the reason s.s. sparks
tend to be not so long as spark-gap-driven sparks relates to the slower
voltage-rise capability of s.s. systems. With the very fast rise
available from spark-gap coils, air inertia "bottles up" the spark for a
brief time during which the top electrode's voltage may rise considerably
higher than it would otherwise. Then, the higher charge acts to extend
the spark's length beyond that which the electrode's effective radius
would normally support. I have reached that conclusion only after some 5
years' worth of effort in developing my s.s. system. But at 73, I'm not
much bothered, happily, that my *bippy* may be shorter than someone
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