Re: High-input SSTC: Possible?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kchdlh-at-aol-dot-com>

In a message dated 12/22/2001 6:08:15 PM Pacific Standard Time,
tesla-at-pupman-dot-com writes:


>
> Subj:High-input SSTC: Possible? 
> Date:12/22/2001 6:08:15 PM Pacific Standard Time
> From:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> To:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> Sent from the Internet 
>
>
>
> Original poster: "Matthew Smith by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <matt-at-kbc-dot-net.au>
>
> Hi all
>
> Looking at various SSTC schematics, I see that we are generally
> switching about 120V; is it possible to use a stack of MOSFETs, or
> whatever, to work with a larger power source, eg., rectified MOT, to
> build an SSTC with a lot more "oomph"?
>
> Cheers
>
> Matthew Smith
>
>



Sure is...but as Terry has commented upon, at  considerable cost.  Here's a
description of my coil:

Solid-state Tesla Coil Design in Progress:

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

2.  Physical size, 2 ft. square x ~5 1/2 ft. tall.

3.  Primary design:

3.1  3 equivalent untuned electrical turns driven by power MOSFETs; right now,
changing to 4 turns.

3.2  Present configuration, 24 pairs of 500 V, 85 A MOSFETs in a patented
circuit (U.S. #6,069,413) switching 4, ~150 Vdc power sources in series into
the 3 equivalent primary turns at the secondary’s Fr.  When fully configured,
36 pairs may be used.  There are 6 pairs of MOSFETs plus associated
energy-storage capacitors per printed circuit board.  With each such board is
associated an additional circuit board holding the MOSFET-drivers and an
off-line switching-current-source to both charge the capacitors and keep line
current limited to a selected maximum.  Right now, I'm adding 1 more pair of
boards, yielding a primary containing 5 groups of MOSFETs, 5 groups of
storage-capacitors and 4 equivalent primary turns.  This ends up applying ~600V
at the secondary's Fr to the 4 untuned primary turns.  The MOSFETs are all
effectively in series-parallel; it may ultimately be that I will not need them
all in which case I can eliminate some of them that are in parallel.

4.  Secondary design:

4.1  12.5” coil diameter x ~38” height on a sonotube form.

4.2  Approx. 550 turns of 20 ga. wire space-wound.  Q = 80-100 -at- ~140 KHz
resonance.  See www.pupman-dot-com postings of 8/19/00 and 8/20/00, HERRICK’S
RECIPE FOR A SPACE-WOUND SECONDARY.

4.3  Top toroid,  a 6” x 24” commercially-produced toroid.

5.  Features:

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 40/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 to air, currently ~30”.

5.6  Present spark duration, ~6 ms.  Approx. 300 us secondary-voltage rise time
to commencement of spark.


Ken Herrick