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Re: [TCML] Pig SISG - Day 3
To help prevent those nasty pri strikes on high power coils try this:
Make up some stands that are approx 3 inches higher than your primary and
space them at 120 degrees around the coil. I usually place mine approx 2
ft out away from the pri. I make mine out of wood dowels and use a 14 AWG
wire running up the dowel to the top where I terminate it with a sewing
machine needle. The 3 stands hook together at the bases with cheap
bananna plugs and receptacles.
This gives the stray sparks a definite strike point so they won't go near
your caps, etc. It's cheap, easy, and works great. Eliminates the
necessity for strike rails attached to the oscillator base.
Dr. Resonance
> 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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Dr. Resonance
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