RE: Counterpoise and MMC demise

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

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

I can't imagine any effect on what happens to a capacitor by changing the 
nature of the RF ground.  I'm sure it was something else.

A 6kV NST is a fairly low voltage.  How many static gaps in series, and how 
wide each, were you using?  Could the gap just have been set too wide?

I'm not familiar with the Arcotronics caps, but Wima FKP-1's are certainly 
MMC-worthy.

Gary Lau
MA, USA

  -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com]
Sent:	Wednesday, June 18, 2003 10:04 AM
To:	tesla-at-pupman-dot-com
Subject:	Counterpoise and MMC demise

Original poster: "Mudford, Chris by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <chris.mudford-at-agresearch.co.nz>

Hi all

Is using a counterpoise hard on MMC capacitors?  My coil is only small
6kV/30 mA NST, multiple static gap, MMC, copper tube flat primary
(tapped at 3.5 turns), 3.5" secondary with small spun toroid.  When
running it at home using a quarter inch rod about 1 foot into the ground
for the rf ground I have had no problems.  Without changing tune or
anything other than using a 2.5 x 3 foot piece of steel triangle mesh
(like used on gang ways to walk on) as a counterpoise I blew a capacitor
in my MMC.  Was it simply time for it to go?  Last time I used a
counterpoise I blew a capacitor aswell.  The safety gaps weren't firing
nothing was warm and it hadn't been running for long and was giving
multiple 6" arcs (not great performance I know, but I'm working on that
one).

The MMC is 4 strings of 6 capacitors with 33 Mohm resistors across each
capacitor.  The capacitors are from RS (114-468) and are Arcotronics
Film-foil polypropylene 1500V- 0.022 uF 1800 V/us.  Total of ~15 nF for
resonant.

  >From what I know now I never built this with much safety margin for over
voltage.  Is it coincidence or could the use of the counterpoise be to
blame?  Is it worth persisting with this MMC (its run for probably 40
minutes in total since replacing the last individual capacitor)?

What MMC design specs would anyone suggest for this coil if I was to use
WIMA FKP1-0.068 uF 1600 V- 650 V~ capacitors?  This coil is only to play
with while building a bigger coil, but its good to set up in 5 minutes
to show people.

Look forward to your response.

Cheers, Chris (NZ)