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Re: power SSTC plans?
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[kch] Repeating, more or less, a prior posting of mine, here is a
run-down of my design:
Solid-state Tesla Coil Design in Progress:
1. Input, 117 VAC, 60 Hz, 0-1800 W.
2. Physical size, 2 ft. square x 5 ft. tall.
3. Primary design:
3.1 One equivalent untuned electrical turn 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 pulsed 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
capacitors.
4. Secondary design:
4.1 Present design: Approx. 10” coil diameter x 39” height; overall
secondary dimensions, 13 in. dia. x 40 in. Approx. 1260 turns of 18 ga.
(.04” dia.) tinned Cu wire arrayed in 120 flat “pies” of 10 1/2 turns/pie
plus 60 additional turns of 14 ga. phosphor-bronze spring wire. The 14
ga. turns “guard” the 18 ga. turns & forms against inadvertent sparking
from the outside. Turn-turn air spacing, n.l.t. 0.1 inch.
4.2 In process of building a conventional "Sonotube" 12" x ~48"
single-layer secondary for comparison & possible substitution. My current
secondary is quite complex and I fear it may not withstand the 2x or 3x
voltage, without corona, when I augment the primary apparatus.
4.3 Top toroid, 4” c.s.d.x 20” o.d. 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.
5.6 Present spark duration, ~6 ms, selectable.
6. Dissemination of plans:
6.1 I plan to offer my construction plans, 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.
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.
Ken Herrick
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On Mon, 14 Aug 2000 07:55:10 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Jan Florian Wagner" <jwagner-at-cc.hut.fi>
>
> Hi,
>
> are there any plans on the web on building higher power (>100W) solid
state coils?
>
> I've seen many schematics for the simple TV flyback coils, but what I'm
searching for is some powerful RF frequency generator with low voltage to
bottom feed a small, maybe 2"-3" dia coil.
>
<snipped>
> And, how does base feed work - do you hook up the secondary coil base
directly to the rf generator, a bit like an antenna? Or connect a helical
primary below the secondary base and connect the generator to it, so
there's alternating magnetic field through the secondary plus a RF
> signal at secondary base?
>
> Jan Florian Wagner
[kch] I've concluded that, for direct drive from transistors, direct
base-feed to the secondary has too high an impedance. My power MOSFETs
"like" current and "hate" voltage; hence my 1 primary turn: lots of
current, minimal voltage. You connect the bottom end of the secondary to
earth-ground unless, as in my design, you take a bit of the current there
and use it to syncronize your excitation.
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