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Re: Terry's Little SISG Research Coil
Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>
Is there a particular reason why you are using a resistor instead of an
inductor for current-limiting on the high side of the DC power supply in
your small SISG coil? The resistor is described in your "Small SISG Tesla
Coil" white paper, but not why it is used instead of an inductor. In this
specific application, what are the benefits and drawbacks of resistance vs
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Tuesday, July 18, 2006 6:11 PM
Subject: Re: Terry's Little SISG Research Coil
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
At 120 BPS it is 7 inches.
240 BPS is 10 inches.
360 BPS is 11 inches.
With the two MOT system I was getting almost exactly 6 inches per 900V
step in firing voltage. ie. 6, 12, 18, 24, 30 inches. So once the
voltage breaks away from the toroid proximity, the distance seems to be
proportional to firing voltage.
The firing voltage does not vary nor does the bang power.
BTW - I never made a schematic of this coil :o) But here is one now (I
see schematic is spelled wrong...):
At 09:35 PM 7/17/2006, you wrote:
At 139 kV what is your spark length to a grounded rod? Interested in the
kV/inch for this coil.
Long long ago, in a time I forgot,... I started working on a "little
research" Tesla coil... A very simple, reliable, repeatable, solid state
thing... Big sparks were not the issue, but rather a coil always "ready
to go" in any situation. No lost cables, damaged secondaries, blown
Well, the SISG was made to run it, which was like a four month "delay"
:o))) It's parameters are probably more accurate and better known than
any coil on Earth ;-)) It's output is deliberately "limited" so scopes,
test equipment, and computers can be near it.
A paper describing it is here:
Forgive if it is "technical"... This is a VERY "technical" coil...
It runs rock solid and is totally repeatable, even if I go back and
measure the parameters after long running. No other coil I have every
had has been totally "repeatable"...
It is an "odd" thing... It runs at 120, 240, 360 , more... BPS depending
on the variac setting (as designed ;-)) But the "gap is "silent" (Well,
you can hear the magneto constriction if you try) and the running is
"perfect". It does not sputter, hiss, or vary. It runs almost like a
DRSSTC but no electronic "brains"... I actually seems far more "stable"
than my DRSSTC... It is super cool for corona stuff!! Peak voltage is
139kV, and yes, it really IS that accurate!!! I suspect much of the
seeming stability is due to it being pretty lower voltage.
It will not breakout without a "point". Cool for many tests... But if
you were wanting a "real" coil, just add another MOT to double the
voltage >:-))) Higher bridge PIV too... But "I" kept it tame with just
one MOT so I would not blow it up like I have all my "other" research
It is pretty "cheap"!! I just used SISG boards I had as scrap. Just
very common stuff and four CD caps... I spent ~$75 on stuff for it
mostly the Lexan, odd parts, and pretty woodwork ;-)) There is not a lot
http://drsstc.com/~sisg/files/SISG-coil/P7150184.JPG (big file)
I should note three things I found of note...
1. The secondary coil was not effected at all in any measurable way buy
the massive MOT nearby.
2. The secondary has a "Q" of 213 and an AC resistance of 147.6 ohms
which is vastly "better" than all the programs predict... I don't know
why... I have measured that in several ways now and my measured numbers
hold solid and the separate types of measurements agree to 5%. Maybe I
just made it special good ;-))
3. The primary resistance is 0.155 ohms. 0.06 ohms of that is the SISG.
I used 12 gage stranded wire for the hookups in very short lengths and
big brass for the connections... But there is 0.095 ohms in the primary
coil and wiring. Not a big deal, but "significant"... The SISG stuff
places new demands on primary resistance. A conventional spark gap at 3
ohms would render the primary's "Q" at about "1" so it would not even run
Coil Power 53.1 watts
SISG 9.55 watts
Primary Loop R 15.12 watts
Secondary Rac 2.4 watts
Arc 25.9 watts
If I could quench on the first notch (11.2uS), this changes to:
Coil Power 53.1 watts
SISG 6.89 watts
Primary Loop R 10.9 watts
Secondary Rac 2.88 watts
Arc 30.8 watts
I looked into quenching by careful selection of R4 on the SISG. However,
the voltage drop at the gate and the currents required per time did not
add up. The e^-t/RC curve does not have the drive at the right times to
quench but still sustain the "good" currents. At higher currents, a low
R4 (like 60 ohms) just will not work for fast quenching :-( It will take
So that is what I have been doing this last six(!!) months...