Re: New coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John Richardson" <jprich-at-up-dot-net> 

Hi Bart,

Thanks for the tips.  I was using the Geek chart, and I assumed that it was
on the money as far as NST safety goes.  Is this not so?  Regardless, I'm
going to start doing the calculations manually, or try your MMC program.  I
appreciate all of your thoughts, and am going to splice on another two turns
and retap a little further out.  Still, with one shorted cap and being a
little out of tune, 40-44 inch consistent streamers are flying around, but I
think I can do a lot better with a little redesigning.  Might see how much I
can get out of a 12/60 before dedicating a 15k trans to this coil.  Anyhow,
thanks again, but I've got to head to the basement.  Got an 8" form that
needs winding!

Take care,
John

 > >Upon first fire up, I tapped at turn 14 1/4, as I usually start from the
 > >outside in when first firing.  This happens to be the number of turns I
 > >wound up with before running out of a full roll of tubing.
 >
 > Yep, that's how most of us do it. With the small toroid, should tune in
 > at  15.9 turns (which you don't have). On this number I guessed at the
 > secondary turns at 1480 and used a primary cap size of .0188uF. So if
 > that's the case, you would need more turns than you currently have to get
 > this coil properly tuned.
 >
 > >   Instant multiple
 > >streamers, maybe four or five at a time, with the longest consistently
 > >hitting the 36" mark.  Within a minute or so, a capacitor lead arced to
the
 > >muffin fan, killing it.  I set up another fan, and proceeded.  Within
 > >another minute, I heard a sound like a rifle shot every 15 seconds or so.
 > >Turns out the last capacitor in the bank was arcing to a bolt which joins
 > >this same cap to a lead to the primary.  The arc had to jump over an
inch,
 > >and I figured that since both the last capacitor and the wire going to
the
 > >primary SHOULD be at the same potential, I wouldn't have a problem.
 > >Why did
 > >this happen?  Even though there is a hole in this cap, there was no loss
in
 > >performance.
 >
 > Sounds like you killed the cap. I've killed one MMC cap (a long time ago
in
 > a galaxy far far away). It blasted a whole in side of the cap. Sounds like
 > what our describing. It's possible that you overvolted the cap? The cap
 > bank rating is 16kV, the transformers peak potential is 16.97kV. Your bank
 > is kind of "on the edge", but this can become aggrivated by the spark gap
 > distance. Did you set the gap by checking the NST's ability to arc across
 > the gap (before hooking up to coil)?
 >
 > In any event, the cap is dead, and now your down to 7 caps
 > (.0214uF=assuming 0.15uF is value of single cap). Cap bank rating drops
 > down to 14kV (you'll need to decrease the gap for the lower voltage). Or
 > get more MMC's. I personally would try to get 2 strings of 12 caps for a
 > voltage rating of double the NST (and this is modest, not greatly
 > overrated). Also, that bank would yield .025uF and tune about 14 turns.
 > I know this sounds overboard for MMC's, but I'm part of the croud that
 > would rather over-rate the cap rather than hope all goes well.
 >
 > One thing in your favor here, the larger cap value of .0214uF (7 cap
 > string) would put you in at about 15 turns (still need another turn of
 > primary to make this). For what it's worth, my latest MMC of .025uF has 3
 > strings of 18 caps (54 caps), which has a bank rating of 36kV (and I still
 > worry, but no cap deaths).
 > >