Re: Solid state spark length record?

To: tesla-at-pupman-dot-com
Subject: Re: Solid state spark length record?
From: "Kennan C Herrick" <kcha1-at-juno-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Fri, 21 Apr 2000 12:04:19 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

In answer to Keith, here is what I am working on:

Solid-state Tesla Coil Design in Progress:

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

2.  Physical size, 2 ft. square x 59 in. 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
patent-pending circuit.  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  Approx. 10” coil diameter x 39” height; overall secondary
dimensions, 13 in. dia. x 40 in.

4.2  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.

4.3  Top toroid, 4” x 14” aluminum duct, ultimately to be replaced.

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, yielding a “quality”
figure of 3.8 for spark length in mm per primary Volt.  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.

Ken Herrick

On Tue, 18 Apr 2000 17:16:27 -0600 Tesla List <tesla-at-pupman-dot-com> writes:
> Original Poster: "Keith" <k-clark-at-pacbell-dot-net> 
> 
> Does any one have detailed plans for a H-bridge solid state driver 
> project?
> How about the setup that produced 57inch sparks?
> Any info would help.
> Thanks
> send to: k-clark-at-pacbell-dot-net
>snipped<

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