Re: fullbr.SSTC air core pri turns?

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kcha1-at-juno-dot-com>

Jan (& anyone else interested--tho few, it would seem...)-

I am driving 3 (equivalent) primary turns with 1000-1200 VPP at about 140
KHz.  Of course, I use a >bunch< of power MOSFETs.  I seem to have found
that 3T is about right.

Here's a run-down of my spec's so far, on 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  3 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) delivering ~450 A through the primary. When
fully configured, 36 pairs are to deliver ~670 A. There are 6 pairs of
MOSFETs plus associated energy-storage capacitors per
horizontally-arrayed printed circuit board. With each such board is
associated an additional "daughter" circuit board holding the MOSFET
drivers and an off-line switching-current-source to both charge the
capacitors (1800 uF each) and keep line current limited to a selected
maximum.
4. Secondary design:
4.1  12.5" coil diameter on sonotube x ~40" height.
4.2 Approx. 550 turns of 20 ga. wire space-wound. Q = ~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, commercial (Landergren) 6" x 24".
5. Features:
5.1 Highest voltage to ground ever present anywhere in 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 Present spark-length to air, ~30".
5.6 Max. spark duration, ~6 ms depending on rate. Approx. 300 us
secondary-voltage rise time to commencement of spark.  Currently, I am
working on an adaptor to modulate the spark with audio using an ISD1420
analog shift-register sound-recording IC.  The breadboard works like a
champ for freq's between ~400 Hz & ~2500 Hz.  I expect my first selection
to be the "Battle Hymn of the Republic", 1st 2 stanzas--just for the hell
of it (edited, perhaps, to "the heck of it") since I am not religious.
6. Dissemination of plans:
6.1 I offer my construction plans, for a modest dollar amount and for a
design based on my current one.  See my postings on 6/23/01 & 6/24/01. 
See also
 
http://hot-streamer-dot-com/temp/KCH_tcg1.jpg
http://hot-streamer-dot-com/temp/KCH_tcg2.jpg
http://hot-streamer-dot-com/temp/KCH_tcg3.jpg
(if they're still up) for pic's of the coil.
As to the location of the primary, I believe that--at least, for a
non-resonant one--closely coupled and concentric with the secondary is
the best choice.  You want to couple the max. flux into the secondary.  I
recall having found, using a 1-turn test loop, that about 1/3 up the
secondary would yield the max. secondary voltage (from a test
oscillator).  But then, insulation, pri:sec becomes a problem. 
Ken Herrick

On Fri, 26 Oct 2001 08:01:55 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Jan Florian Wagner by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
> 
> Hi,
> 
> about determining the initial turns on the primary coil for a 
> full-bridge
> with a direct helical TC primary coil drive: is there any constraint 
> that
> gives the minimum number of turns on the primary? 
> 
> I must say I feel a bit uncomfortable about driving so few uH's at 
> 100kHz
> from 640VppAC - I mean, seems like it'd be destined to fry...?  :o)
> Especially when the secondary is not in place.
> 
> Btw, is there any reason why one shouldn't place the primary inside 
> the
> secondary coil former? 
> Just thinking that insulation wouldn't be an issue then, and as a 
> bonus
> it'd give a bit less stray inductance, AFAIK...?
> 
>  - Jan
> 
> --
> *************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla
> 
> 
> 
> 
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