Re: 3rd light- Help!

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi again Simon!

Date: 17 January 2001 13:58
Subject: 3rd light- Help!


>Original poster: "Simon Yorkston by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <quantumx-at-ozemail-dot-com.au>
>
>Hi again all.
>I'm halfway through my 3rd light tests, and I'm having no
luck, at all.
>Here's the synopsys.
>
>The NST+Protection, safety and SSPG are working great. I
rebuilt my SSPG,
>and have got it running on 6 gaps at the moment, sounding
great.


Splendid!

>>>>>The only thing I can narrow it down to is the MMC. You
might remember
>there was one 'suspect' cap [it arc to the ground [eg,
terran, ground]. I
>can rule this out, because the bleeder hasn't fried, which
it would do if
>the cap died. the MMC is 2x15 .0047uf caps.


Hmmmmm.  You don't mean 2 strings of 15 times .047uF do you?
My calculator says 2 strings of 15 times .0047uF is only a
meagre 627pF which is a bit mingy for a 15/30. I'll assume
it's a zero too many, in which case you have 6,27nF which is
fine. That will give around 0,6J per bang on 14kV (about
what you'll have after the filter resistors have done their
bit) which should be enough for some serious arcs. A mere
627pF will leave your coil gasping with a bare 60mJ per bang
and difficulty breaking out if the toroid has a minor
diameter of four inches or more - though my 10/50 coil will
give at least a foot of spark even at that level.  Also,
627pF is going to need a _lot_ of primary.

I'm not sure I'm with you on your logic re the cap dying and
the bleeder frying.  If the cap had shorted internally there
would be no great increase of current through any parallel
bleeder resistor and no cause for the resistor to give up
the ghost.  If the cap has arced to ground, maybe you ought
to check it if only to give it a clear bill of health.  If
you have a multimeter, remove the cap from the chain and
remove its bleeder resistor, and measure the resistance of
the cap.  It ought to be over 2000Mohms for a plastic cap if
it's good.  If it only manages say 20Mohms I'd ditch it, or
at least measure another cap and do a comparison to be sure
the suspect cap is in the same ballpark with the ones you
know are good.  It may take quite a few seconds for the
meter reading to stabilise at this resistance level as the
measuring voltage charges the cap - but then I expect you
know that anyway.  I know it's a pain to do all the
desoldering/resoldering, but it's the only way I know to be
sure.

We _shall_ overcome :-)

Dunckx