RE: HV cap flashover, :-0 repost

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

The fact that your gap fires when your variac is only at 50% proves that
there is some mains resonant-rise occurring.  If there were none, the
gap would only fire when your variac was at 100%.  Even though .02uF is
LTR, there is still some resonant rise, though I'm also surprised it was
this bad.  So this leads to the next question.  Just how far apart is
your gap?  It should be set such that it will only begin to fire when
hooked up to just the NST.  That there was arcing over 7/8" means that
there is some seriously high voltages preset.  Judging by the resistance
across your caps, it sounds like one or more of them may be toast,
although a bad over-volted cap may not necessarily show anything with an
Ohm meter.  

The good news is that your NST is still working.

Regards, Gary Lau
MA, USA

===================================================================
Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<scepp-at-mts-dot-net>

Help,

my 0.02uF, 30Kv  parallel mmc capacitor is flashing over on my 12Kv -at-
60mA
NST
tesla coil.  It's located under the primary coil, if that matters?,  and
it's made up of 2 rows of 7 capacitors all in parallel, 0.0015uf per
cap.
I tried to make smooth solder connections using extra solder.  This was
going to be my first light, sigh.

I powered it up with a variac,and at 55 - 60 vac input, my 2 gap spark
gap
started to fire, then the capacitor flashed across a solder joint and
opposite conductor.  I fixed the cct board and insulated with glpt all
and
tried again, ---- it flashed across at several other points, all solder
joints to connecting wires that wire up the mmc.  The flash over
distance
was 7/8 inch, holy smokes.

The third try was after I immersed the cap bank under some HV silicone
oil
that I salvaged from an xray machine power supply, same stuff the caps
came
from.   It ran for a bit, voltage even flashed over 3 time across the
mid
windings of the primary conductor.  It's made up of 3/16 inch copper
tubing
spaced 1/2 " c-c, 11 turns in all.  Then it died totally, just
nothing.........  After testing components I found that the mmc has 5
Mohms
acoss it and I had put 2 200Mohms resistors across it, somethings
wrong!!!!!!, I think the cap is dead, tranys good. So I pulled it out of
the
oil and it is drip drying now, quick check in case it was the oil.....,
no
still  ~5 Mohms.     Oh, by the way, at 70volts input , my TC was
spraying
electricity 1.5 feet in all directions, must have been the elbow joints
I
used for the top load!!    :-)

If I'm running LTR, why is the voltage going so high to flash onver 7/8"
across the uninsulated caps and flash across the primary and most likely
kill 30Kv caps??
I'm going to buy different cap, me thinks  ;-)  any insite as to what
may
have happened.

Thanks in advance for any comments, and this group has been really
helpfull in the past,  Thanks you all!!


specs are
  4.25"  24 inch length
26 gauge magnet wire
top load is 4" * 11.5  -- 4 inch elbows
F res= 200Khz
primary is 11 turns 3/16" copper tubing
6.5 " inside ,  18" outside, 1/2 c-c spacing
capacitor is 0.022 -at- 30 Kv   from a xray machine
14 caps in parallel, 0.0015 -at- 30Kv
tranny is an Alason 12Kv -at- 60mA
standard protection cct, alah Terry
dual gap tungsten rod spark gap
very heavy duty wiring!!  :-)

Shaun Epp