RE: Run Failure, need help

To: tesla-at-pupman-dot-com
Subject: RE: Run Failure, need help
From: Gary Lau 05-May-1999 0937 <lau-at-hdecad.ENET.dec-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 05 May 1999 16:36:59 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

>Original Poster: "Andy Cleary" <gemware2-at-dreamscape-dot-com> 
>
>   I had an idea that it may be the coupling, but I being lazy just put on 2
>coats of polyurethane ( I would have to disassemble everything to raise the
>coil).  I tried the coil again on 5/4, and I got a few large bursts from a
>few places in the secondary coil.  I tested it, an it still has continuity
>so I figure it is still OK?

The damage to a secondary that arcs due to overcoupling is not that it
looses continuity.  The damage is that insulating things like wire
insulation, polyurethane, and PVC carbonize (burn) due to the arcing and
become conductive, which promotes further arcing, even if the coupling
problem is fixed.  Complete removal of the burnt stuff is required,
probably difficult to impossible.

>Unfortunately I thing I blew the transformer
>somehow.  After increasing the main gap distance the safety gap fired a few
>times, then the whole thing stopped.  Suspecting the transformer I 'tested'
>it by creating an arc from each HV output to the case, and they both worked.
>I suspect I will try a few different transformers.  I should have mentioned
>before that the transformer is a 15000 v 30ma NST.

A damaged NST may or may not arc to the case, though that usually is a
good test.  It could be that it only fails at voltages generated by the
resonant rise that occurs when the caps are hooked up.  You definately
need to throttle down your gaps, though your NST may not be long for this
world regardless.

>One small flaw that I
>found was that my beer bottle capacitor was rated for .009 uf rather than
>.005!  I based it on an idea I saw in a book, which rated each bottle at
>.0005 uf, so I used ten.  Today I tested it with a capacitance meter, and I
>found the error.  Could that also have contributed to the failure?

The cap value being off wouldn't cause an NST to fail and should be
correctable simply by selecting the proper primart tap.

>One more
>question- for the ground I am using a 14 awg cable attached to a steel or
>iron rod, about 4ft in the earth.  Is that sufficient?  Thank You,
>
>-Andy

It depends upon how long the cable is.  If it's short (<10 ft) it will
work, but this is not a black and white thing.  It won't work as well as
a 10 ft 2AWG cable, and this won't work as well as an 8 ft rod with 2AWG
cable.  But any ground scheme will work somewhat, and this is unrelated
to the overcoupling and too-wide gap problems.

Regards, Gary Lau
Waltham, MA USA