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Re: [TCML] SISG First Light
Originally, I think they were in the $8 range. But 1 year later, they
were over $20 each and hard to come by and as time progressed, they were
closer to $30ea. When I bought Marks boards, I decided to pick up the
components myself. I waited for a time to see if prices would drop down
(it didn't). I think Mark picked up a batch later on for a decent bulk
price and was able to sell them at a very low cost ($10 each or
something like that) and had offered to sell me some at that price. I
declined the offer only because I couldn't afford the expense at the
time (without my wife killing me). So I waited. Then I got tired of
waiting and started looking for an alternative. That's when I came
across the Fairchild IGBT's. The specs were close enough to be a drop in
replacement and it was only the power dissipation which I worried about.
When Terry picked the IGBT for his SISG, he went with the best out there
at the time and the price back then was doable. The main difference is
the die size which dictates thermal dissipation. My IGBT's have a
smaller die size and will run warmer, but if they have ample heat
sinking and air, then it's manageable. After the run, I put my hand down
by the air exit hole in the cabinet (with the fan still blowing) and the
air was only a slight temp difference, but barely noticeable.
Of course, I'm just starting out. If I double up on the current, maybe
then I'll see an issue or at least a noticeable change in temp. I think
I'll bring home a temp probe and attach it to one of the IGBT's and
measure how hot it actually gets. This was a long continuous run, so the
IGBT's had plenty of time to heat up to the maximum allowable temp under
the conditions and stabilized (which I think was relatively cool).
That all sounds wonderful, definitely so. It is truly a marvelous
invention by Terry.
What is the main differences with this new IGBT as compared to the
type, the type that Mark Dunn was selling for a time?. I guess the
rating is a little lower, but the price is much lower? Is that about
of it? I seem to remember the other IGBT's were about $10 each?
From: bartb <bartb@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sun, 19 Oct 2008 6:19 pm
Subject: Re: [TCML] SISG First Light
I just finished installing the 6th SISG board and running the system.
I have k low at 0.112 (meas.). I'm running low Cp at a measured 65nF.
I just came in from a 10 minute duration run with the coil. It ran
flawlessly throwing out 5 foot free air streamers at 200V/11A input.
It looks like (in my case anyway), your spark length equation holds
well for my SISG coil. During the run, I ran at higher and lower
voltages and compensated with current. In both cases, it didn't make
much of a difference (I could do about the same with both extremes).
One thing I noticed is when I increase power, pps would increase and
there is a spot where your just on the edge of the coil running a nice
120 bps (as well as my ears could detect), but when I threw more power
at it, the coil began to sound odd. I could tell the sisg was not
firing smoothly. Kind of a DRSSTC sound to the sparks. So I kept it at
that edge of running smoothly and just let it run.
I did have a fan blowing inside the chamber. I'm using a Fairchild
IGBT on the boards (HGTG18N120B). Mouser has them for $5.30ea in
quantities of 1. Mouser has 283 in stock and nearly 10,000 showing up
in a few days, so these IGBT's are probably the way to go with the
SISG boards (IMHO). They probably run a little hotter, but with air
cooling, that's no big deal. Here's the data sheet.
Anyway, a great continuous 10 minute run and no problems at all. I
think I see why large Cp would be best for an SISG. Had I double the
tank C, I could have doubled the current at the pps where the IGBT was
happy. But as far as running ability with a low Cp, there are no
problems that I can detect. So an SISG can be a direct replacement for
a conventional spark gap.
I'm happy with my SISG coil. I designed it for no primary tuning
(ribbon), so I'm using the full turns. All I did was raise the toroid
2 inches. I measured within 1kHz of the calculated value, so it all
worked out as planned.
I should note I am still using a breakout point. It did breakout of
the 9" x 30" toroid with the 6th board, but it=2
0was not consistent.
Another very important point to note. After my 10 minute run, I went
and asked my wife about static on the TV. There was "NONE" she said!
What an improvement! Might make the "perfect" spark gap replacement
for those who live in apartments.
So kudo's to Terry Fritz for inventing the SISG and to Mark Dunn and
others who took the SISG to new levels.
Congratulations on your initial results. I have the SISG boards and >
but have not done anything further yet.
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