[TCML] Pig SISG - Day 3

[FIFTYGUY@xxxxxxx]

Folks-
 
    Well, I only had a little time after I got off work  before it got dark 
around here. So I only had time to check a few things before  running again 
tonight. 
    Once again, I decided "I gotta have more cowbell!"  So I added one of the 
Maxwell 37667's, for a total primary capacitance of .105  uF. To quote 
Richard Hull, "When we hear of a builder who uses more than .1 uF  of capacitance, 
we wonder about the builder." Well, it certainly ran better  with even more 
cap!  I had a friend over tonight who saw Nemesis run in its  heyday, and he said 
the little 6" coil on my driveway was more impressive - in  its own way. 
    It only ran for about a minute before it died  again. I forgot to put up 
the piece of sheet steel along the side of the primary  caps, and another 
nasty strike curved around and hit "down there" again. After  that, nothing. The 
current would peg, but there was no output. I didn't see any  obvious damage to 
any components. All the IGBT heatsinks were uniformly warm.  The rectifier 
was in one piece.
    I put the stuff aside, and ran the X-ray  transformer into a Jacob's 
ladder for the audience. Then I decided to see if I  could get the 6" coil running 
again. 
    After a few tries, with an occasional faint corona,  it stopped pegging 
the meter at low variac settings, and started acting like it  was triggering at 
high voltage again. Then it started to run, but at only  partial power. So I 
shut it down, and checked the rectifier bridge. Sure enough,  another leg was 
blown to bits - it was like the solder joints had melted in  several places. 
The string of 40 diodes was now in five pieces! 
    So again I replaced the bad leg with another "bar"  rectifier from that 
AM radio station. And no more failures for the rest of the  night! Those HVCA 
pucks are looking more attractive... might be excessive RMS  current is the 
culprit?
    Well, I didn't even bother tuning the thing with  the primary tap. And I 
still haven't played with the coupling. But the corona  was so bad from the 
strike ring to the secondary, that it started arcing from  the top third of the 
secondary to the opening in the strike ring. Mind you, I've  got a 2x10" 
toroid at the top of the secondary, and the 8x36 less than a foot  above that. The 
secondary arcs were so bad, it scorched the varnish cover, and  bubbled 
through in several points. At the worst spot, the varnish caught fire,  the wire 
glowed halfway around the coil, and soot covered everything from that  point up. 
One strike somehow lit up the entire top third of the secondary under  the 
varnish with spiderweb turn-to turn sparks! When I put out the flames, I  figured 
everything was done for the night.
    Then I remembered the recent thread here about the  futile, if not 
downright harmful, effects of running with a strike ring. So I  took mine off. Wow, 
what a tremendous help!
    No more corona from the secondary! No more  secondary strikes! No more 
glowing secondary turns! And it barely stuttered when  it hit the primary! In 
fact, it just made some staccato blasts as the primary  arced turn-to-turn. Now 
I feel the only place I need a "lightning rod" is  *under* the primary so it 
doesn't hit components on the bottom!
    I added several breakout points to the toroid. It  seemed to really like 
having the multiple breakout points, and in fact seemed to  run the same from 
three or four simultaneous breakouts as it did from one.  Probably that high 
BPS. 
    I noticed if I ran for about 5 minutes steady now,  the heatsinks 
actually got too hot to touch! It also seemed like the BPS started  to creep up, and 
the sparks started to get weaker. So I may be finally stressing  the IGBT's. 
OTOH, after it cools for five minutes, it starts back up again just  fine. A 
few fans might be all it needs. Now I just gotta find a muffin fan  that runs 
off 22,000 volts of unfiltered DC...
    Maybe when I have time to run it again (in a coupla  days) I'll try it 
with .150 uF of primary cap, and then put some filtering on  the DC side for 
Scott Bogard's amusement. Anybody want to suggest how much  filter capacitance I 
should add? 
    Sparks must be bright - two of my neighbors who  were inside their homes 
thought I was doing some more welding!
    Nobody complained about any kind of TV, radio, cell  phone, or computer 
interference. Only one digital camera out of four had a  difficult time  - and 
I'm not convinced that it was an interference  problem. But the SISG seems to 
run very "clean" compared to a normal spark  gap.
 
-Phil LaBudde    
Center for the Advanced Study of Ballistic  Improbabilities



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