I managed to debug my rebuilt coil to the point I'm getting nice arcs.
15/90 NST. 41.8nf cap. Primary is 17 turns of 1/4" refrigeration tubing
spaced 1/4" apart. Using an SRSG consisting of a 1/30hp synchronous
motor running at 1800rpm, a 7" G10 wheel, and eight 1/4" tungsten carbide
electrodes.
Through painful trial and error (painful because I had to kneel on my
garage floor) I managed to tweak the timing on the SRSG so that the
safeties stopped going off. Though I wound up leaving it in 240bps mode.
I figured I only have 45 degrees of "play" instead of 90. Proved to be
easier than tweak the 120bps setup, 2 or 3 degrees at a time, then trying
to figure out if I had the turning straightened out correctly. Trying to
separate each problem and solve it in turn rather than trying to figure
out how to fix 6 bad things happening at once.
When I finally got to the point where the safety gaps weren't firing, I
still had 2 things going on.
1) arcing between turns of my primary
Never had this problem before. Or if I did it was usually due to some
piece of dirt or spider's web falling onto the primary, or worse, having
my ground connection come free and the arc went between the bottom of the
secondary and the primary.
This is none of those situations, and it does indeed seem to be happening
at the higher power levels.
Now I am at the point of considering that the reason this is happening is
the fact I'm running at higher power levels than before. I tried cleaning
off the primary, dusting/vacumming. Deburring where ever I could find
anything that seemed like a burr. When all was said and done I still had
arcing from the connection point between the MMC and the innermost turn of
the primary.
So, I had some g10 laying around, and also some polycarbonate scraps. I
positioned some of the G10 and polycarbonate between the offending region
and the secondary and other turns.
Well, it flashed over anyway. And interesting: the flashover blew the
polycarbonate scrap clean off the primary. (this is a piece about 2" by
1/2" by 1/2")
Still trying to figure out how to stop the flashover. Any ideas would be
appreciated.
Item #2, and perhaps weirder.
At about 120V on the Variac the spark production is quite nice. No
flashover on the primary - BUT
I started to notice a long-period (like 2-5 seconds) oscillation in the
sparks - diminishing and increasing. It seemed to me like some kind of
weird timing synchronization issue, and indeed, it does "go away" when I
adjust the Freau phase shifter - but then I get other problems. It seems
when I'm in the "sweet spot" for timing, I get this slow oscillation.
Now, I was thinking as well it could have something to do with the
environs. I'm running the coil in the garage and the sparks are ending up
everywhere - like the wood studs, the aluminum garage door, the tracks,
etc. And when it arcs to something grounded, the arcs are brighter, and
I can feel the current draw in the variac. But this effect seems to be
different from the long period oscillation.
Just wanted to know if anyone else has experienced the same thing.
Cheers,
Joe
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