[TCML] First ever Pig SISG.... inadvertently
Peter Terren
pterren at iinet.net.au
Sun Feb 3 17:48:52 MST 2008
It makes sense that the tuning is much tighter with an SISG. There is much
less resistance in the circuit to reduce the Q since the IGBT's have a much
lower on resistance than a spark gap.
Peter
----- Original Message -----
From: <FIFTYGUY at aol.com>
To: <tesla at pupman.com>
Sent: Monday, February 04, 2008 1:25 AM
Subject: [TCML] First ever Pig SISG.... inadvertently
> Folks-
>
> FWIW, last night I became the first person to run a SISG coil from a
> pole pig.
>
> Before anybody gets *too* excited, it was just my medium 6" coil, and
> I
> really hadn't started the evening with plans to use the Pig at all.
>
> Yesterday I finished mounting the SISG4 PCB's I got from Mark Dunn.
> All
> six boards, since I was planning on running at high voltage. I was
> originally
> planning on running the SISG with my 12" pig coil, but I figured I could
> give it a try on my 6" coil first. After all, I've never run anything but
> spark-gap coils before, and if I was gonna fry all that silicon, I wanted
> to at
> least see it work!
>
> I had been using a SRSG with this 6" coil, so I had a 15/60 NST and a
> Maxwell 37667 cap (.030 uF). I hastily made up a bridge rectifier, with
> 40
> diodes in series in each leg (UF4007, 1A 1000V, 75nS fast-recovery).
> Added a 200
> Ohm 100W power resistor in each DC leg to limit the peak current through
> the
> diodes if something went wrong.
>
> Well, I was mighty disappointed when I couldn't get anything to
> happen.
> Only thing that happened as I cranked up the variac was noticeable arcing
> on
> the brushes near the top end. No noise or sparks from anywhere on the
> coil.
> But at least no smoke or tripped breakers.
>
> A quick test showed that the rectifier was in fact working, as a nice
> DC
> arc set fire to an alligator clip gapped on the rectifier output. Hooked
> everything back up and still nothing. This is where having test equipment
> ready
> to go would have been very helpful... and one of several times during the
> evening that I almost threw in the towel.
>
> I thought about it for a coupla minutes, and then figured I might as
> well use the "bigger hammer" method of troubleshooting. After all, it was
> a
> clear, cold night outside on the driveway, and if something's gonna fail,
> I want
> some flames to show me where the problem is! So I disconnected the NST
> and
> rolled out the Pig.
>
> As I was hooking up the pig, I realized I may have inadvertently
> solved
> the problem. I suddenly recalled the importance of having the cap tuned
> to
> the power supply with a SISG coil. But my .03uF LTR cap was only workable
> with
> the 15/60 because I had been running a SRSG. I paused to contemplate
> decreasing the cap size to work with the NST and SISG, but then I would
> have had to
> take the time to increase the primary turns, and would've lost bang size.
> I
> figured hooking up the pig was easier, so that's what I did.
>
> Well, as soon as I lit off the pig I at least got *some* kind of
> response. The neighboring kids showed up, and were very helpful in
> pointing out
> where the sparks/flames were coming from. For some reason everything
> wanted to
> fail on the side of the coil facing *away* from me, and they were on the
> "dark"
> side of the coil not illuminated by the garage lights so they could see
> better.
>
> First off, the primary arced hot to the ground terminals a couple
> inches
> below it. For a few minutes I thought it was inter-turn arcing on the
> primary (which *really* confused me!) until the kids managed to catch it
> and point
> it out. I re-spaced the primary away from this area and that took care of
> that problem.
>
> The *next* problem was interesting. The inner turn of the primary
> arced
> *hot* to the bottom (ground) wire of the secondary. I spaced the
> secondary
> up a coupla inches, and tried intervening insulators, to no avail. I
> thought
> the primary was arcing to the secondary, but on a little more reflection
> I
> realized that it was the secondary arcing to the primary! In my haste I
> had
> intentionally neglected to hook up a grounding wire from an RF ground to
> the
> ground terminal on the coil. I had never run this coil that way before. I
> poked a
> 10" piece of rebar into the wet ground, ran a #10 wire to it four feet
> away,
> and problem solved! I never realized how important having *any* ground
> reference was, but it was a night and day difference with this setup.
>
> I finally got some streamers off the thing - all of 24", and somewhat
> brush-like. That's when I had a sigh of relief that at least the SISG was
> actually working. But it was pretty anemic. The control panel for the pig
> has
> ancient, low-tech meters - a moving vane AC ammeter and a voltmeter. It
> was
> interesting to see the voltmeter climb as I cranked up the ganged variac,
> until
> suddenly it hit the breakdown point of the SISG and the current went to
> the
> ballast limit (60 Amps).
>
> The Pig, by the way, is a 10kVA 14/4kV unit I got from Resonance
> Research. So putting 15,000 watts into a coil and only getting a 24"
> brush discharge
> was pretty pathetic. This wasn't the first time I had run the pig into
> this
> coil, though. A while back I had done almost the same thing, trying to
> figure
> out why I couldn't get the calculated output from this coil with the
> SRSG.
> It seemed to me that it wanted more power. So I gave it "more cowbell"
> with
> the pig. The Pig had also hit the current limit on this occasion, but
> with only
> 50" sparks. The power resistors in the Terry filter glowed bright orange,
> and cracked their ceramic cores when they cooled down. So I knew I was
> putting
> a lot of power *into* the system, I just couldn't figure out where it was
> going!
>
> Last night I got a hunch and changed the Maxwell cap with another one
> I
> had gotten from the same source. But got the same results. Both caps
> still
> read the correct capacitance value, and the coil tuned with the primary
> taps
> where the calculations and the Terry Tuner said it should be. So I added
> a .010
> uF MMC string in parallel to the Maxwell.
>
> After some retuning, *that* made a big difference! The tuning point is
> surprisingly sharp with the SISG. At least, much sharper than it was with
> the
> SRSG. I think that's because the SISG just will not fire until the
> voltage is
> high enough, whereas the SRSG would allow lower-bang discharges to get
> the
> streamer going, which then would add enough topload to bring it into
> tune.
>
> So I managed 60" strikes to ground off the thing before the night was
> over. I have no idea where the BPS was, but it seemed perfectly happy
> running
> almost eh same intensity from two breakout points simultaneously. My
> 8x36"
> home-made toroid is so smooth, if I had no breakout point it wouldn't do
> anything at all! Just faint corona off the strike rail! One piece of
> aluminum foil
> tape, taped *flat* to the edge of the toroid, suddenly allowed
> full-length
> sparks!
>
> No primary strikes, but many hot ground strikes. I did run it for
> about
> half an hour total. Still pulled 60 Amps through the Pig primary. I did
> have
> another little flame when one of the diode strings in the rectifier arced
> over, but after some physical re-location and no repairs the thing worked
> exactly the same.
>
> After all that, the IGBT heatsinks (all 24 of them!) were universally
> "barely warm". At least they were all doing their part. All the caps were
> cold.
> But if I run it again tonight, I'm going to make the entire primary cap
> an
> MMC.
>
> My first solid-state coil! I was very eager to see streamers without
> the
> distraction of a spark gap. I was amazed at how loud the arcs off the
> topload were!
>
>
> ****Many thanks to Mark Dunn and Terry Fritz, for their advice and
> patience!****
>
>
> Here's my SISG tips:
>
> 1. "Maxclips" for mounting the IGBTs work fine. I mounted the heatsinks to
> the board, then put compound on the IGBTs and heatsinks, then dropped the
> IGBTs
> into place on the board, then screwed on the clip, then went back and
> soldered the IGBTs in. I figured this way, everything was in a happy
> clamped
> position before it got soldered solid.
>
> 2. The heatsinks are electrically hot on the SISG4 boards, so I took the
> time to round off the corners to reduce any corona. Probably
> unnecessary...
>
> 3. I used a 47 Ohm (DigiKey P47W-2BK 2W 2% metal film) "charging"
> resistor.
> I used a trim pot for the "turn-off" resistor (DigiKey 3296Y-502LF, 5k,
> one-turn, top-adjust). I measured all of them before I installed them, and
> from
> the factory, they are all set to the "middle", at 2.222 k +/- 1 Ohm!
> Turned
> down to "20%" is about 400 Ohms. I ran them all at the factory setting of
> 2.222
> k.
>
> 4. I put everything together with a 140W soldering gun. I never understood
> the "use a low-wattage iron with heat-sensitive components" theory. I have
> more
> luck blasting it quickly, before the heat has time to spread up the
> lead...
>
> 5. "Balancing" resistors are 1% Metal Film (DigiKey 1.00MXBK 1/4W). I
> figured these should be as precise as possible, after all I'm running 24
> sections
> in series...
>
> 6. When I first went to order, DigiKey was out of the .001 uF caps.And the
> .0012 caps! But the next night, they suddenly had a big stock of the *new*
> .001's (DigiKey PF2104, the -JB RoHS style). So it looks like that little
> supply-chain hiccup has been resolved.
>
> I'll let everybody know what happens when I run the "standard" SISG
> with
> the "real" 12" pig coil. By my reckoning, the SISG shouldn't last long!
>
> -Phil LaBudde
> Center for the Advanced Study of Ballistic Improbabilities
>
>
>
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