RE: Solid state gaps - what happened? (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 6 Jun 2007 22:08:25 -0500
From: Mark R Dunn <teslamark@xxxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: Solid state gaps - what happened? (fwd)

 

Gary:

 

There have been plenty of posts on SISG, but little discussion.

My SISG coil has been in operation since June 2006 and the current technical
info is available at:

 

http://www.teslaboys.com/SISG/index.html

 

I have shipped SISG boards to a number of coilers on the list.

 

My coil uses (2) MOT's and (4) SISG boards(16 circuits X 900volt).

Typically I tap at 13 or 14 circuits so I am running at 11.7 to 12.6 KV
threshold voltage).  The SISG is elegant compared to a spark gap.  From my
perspective the spark gap is history.

 

My camera hasn't produced very good pics of the streamers, but a couple of
weeks ago I did a demo for Steve Ward and Jeff Larson.  Jeff got some great
pics and when I get them I will put them up on the website.

 

My coil normally runs in the basement and I have it severely current limited
to keep the sparks off the walls, sewer pipes, equipment, etc.  Right now it
runs with 3 to 4 foot streamers, but I am only feeding the MOT's around
82-85 VAC.  Cranked up to 100 to 110 VAC, it can do 5 to 6 footers, but I
can't do extensive testing of that indoors and have not had time for
extensive outdoor testing (My kids play Travel Soccer AND Baseball).

 

The quenching has not been an issue.  The waveform decays on its own in
about 40 uS.  As a result we have been able to decrease the gate shut-off
resistor value to as low as 680 ohm.  There are waveforms on the website.

 

One of the tricky issues with SISG is that you cannot independently control
BPS.  (Note: Finn Hammer built a triggered version)  You control BPS by
balancing the tank cap size against the impedance of the transformers.  This
concept seems a bit hard to grasp for some people - I did not get it at
first myself.  When I first fired up my SISG coil, my tank cap was way to
small for my transformer impedance and my BPS was 1200!  Now that I have a
properly sized tank cap, I run around 120 BPS.

 

You mentioned cost...I think you will find that by the time you finish a
good rotary spark gap, the cost is far greater than SISG.  

 

Terry pulled his Piranha site down because of a lack of the lack of respect
that some coilers expressed regarding the safety issues regarding the tank
circuit.  These MOT based designs can push 200 mA into the tank circuit
during charging and because of the diodes SISG is a pulsed DC design.  There
is real danger that the tank cap can remain charged on shutdown.  I have
checked mine with HV probe and it takes about 60 to 90 seconds to discharge
thru the safety resistors paralleled with the caps in the MMC.

 

I have ongoing off list discussions with TCML members concerning SISG weekly
and sometimes daily.  The posts I and others have made to encourage
discussion have for the most part been ignored so we figured that most
people were not interested. 

 

Mark

 

 

 

>---------- Forwarded message ----------

>Date: Wed, 6 Jun 2007 15:29:06 -0400

>From: "Lau, Gary" <Gary.Lau@xxxxxx>

>To: Tesla list <tesla@xxxxxxxxxx

>Subject: Solid state gaps - what happened?

 

>Just about a year ago Terry Fritz came up with a very clever, modular

>IGBT-based replacement to the static spark gap.  While the price tag was

>steep and far more complex than conventional gaps, the reported

>efficiency gains seemed hard to ignore.  It wasn't clear to me if the

>SISG was truly a drop-in replacement to conventional gaps, but it seemed

>to hold great promise, considering the ever-decreasing cost of silicon.

>I recall there was ongoing work on triggered versions too.  I don't

>recall if quenching (or lack there-of) was thought to be an issue.

 

>Now a year later, not a word to be heard on the topic.  I'm just

>wondering - was the cost just too high and the practical efficiency gain

>didn't merit the cost, or if one is going the spendy/complex solid state

>route, DRSSTC's do better, or did we just forget about it without Terry

>to tout it?

 

>Regards, Gary Lau

>MA, USA