RE: HV cap flashover, :-0 repost

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <biomed-at-miseri.winnipeg.mb.ca>

Comments added to last reply
Shaun Epp

>To: tesla-at-pupman-dot-com
>Subject: RE: HV cap flashover, :-0   repost
>Message-Id: <4.1.20011029065020.00a32008-at-pop.dnvr.qwest-dot-net>
>Content-Type: text/plain; charset="us-ascii"

>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?

My spark gap was set for low voltage,.. 3/16" across 2 gaps, for a total
gap of 3/8", as you must have guessed is a static gap, but tungsten.  I
wanted to test is at lower power settings before running it at the full
120volts in.  This is what I was going to do just before it died.

>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.

I don't think fixing my existing cap would be worth while, Do you?,  is it
possible that by running it at lower power, that I set up additional
resonances?, I'd have to look at the Mains resonance info again,... I guess
it shouldn't make a difference.  Could these caps that I'm using be doing
it?  They look like fat disk capacitors  1/2" thick and 1-1/8" diameter,
I've paralleled 14 of them, and they servived the external flashovers :-).
>The good news is that your NST is still working.

YUP!!


>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