Solid-state system

["Kennan C Herrick" <kcha1-at-juno-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

I revise herewith my run-down on my current T.c. design, in light of my
decision to go with a conventional secondary (see HERRICK'S RECIPE FOR A
SPACE-WOUND SECONDARY, posted today):

Solid-state Tesla Coil Design in Progress as of 8/19/00:

1.  Input, 117 VAC, 60 Hz, 0-1800 W.

2.  Physical size, 2 ft. square x 68" tall.

3.  Primary design:

3.1  One equivalent untuned electrical turn (consisting of multiple
conductors) driven by power MOSFETs.

3.2  Present configuration, 12 pairs of 500 V, 85 A MOSFETs in a patented
circuit (U.S. #6,069,413; you can access that on the Web via
http://www.patents.ibm-dot-com/).  When finished, 36 pairs are to deliver 3x
the present pulse-burst primary current of ~220 A.  There are 6 pairs of
MOSFETs plus associated energy-storage capacitors per printed circuit
board.  With each is associated an additional circuit board holding the
MOSFET drivers and an off-line switching current-source for charging the
energy-storage capacitors to 160 V.

4.  Secondary design:

4.1  A conventional 12 1/2" dia x 52" space-wound secondary (20 ga.,
.032" dia wire spaced ~ .05" c.l. to c.l.).

4.2  Top toroid, 4” c.s.d.x 20” o.d. corrugated aluminum duct, ultimately
to be
replaced with something smoother.

5.  Features:

5.1  Highest voltage ever present anywhere in primary circuit, 160 DC. 
Highest MOSFET turn-off transient, n.g.t. ~400 V.

5.2  Self-tuned:  Secondary is the resonant element in a feedback
oscillator that incorporates the power MOSFETs.  Always dynamically
tuned.

5.3  Spark rate continuously variable from 1 per button-press to 10/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  Present maximum spark, ~24” to the ground rod.  Objective, ~3x that
spark length with 3x the primary current applied.

5.6  Present spark duration, ~6 ms, selectable.

6.  Dissemination of plans:

6.1  I plan to offer my construction plans for the primary apparatus, for
a modest dollar amount and for a design based on my current one, as soon
as I can—I hope within the next six months.  I have to procure, assemble,
wire up and debug 4 more pairs of circuit boards.

N.B:
The present qty of 24 MOSFETs is overkill, for the ~220A of pulse-burst
current, but they will have to carry the ~660A ultimately, along with the
added ones.

Ken Herrick

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