Re: Help! Suicidal Secondary

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 1/6/02 2:48:13 PM Eastern Standard Time, tesla-at-pupman-dot-com
writes:

Winston,

I think you are seeing the effect of a large bang size, in conjunction
with a high hold-off voltage (large toroid).  You may need to make the
secondary about 35" tall to get rid of the racing sparks.  This is why
I like tall coils for low BPS.  Low BPS is very efficient, but makes
the coil behave like a "larger coil" in a sense.   Using my 24" tall
secondary at 120 bps,  I used to start to see some racing sparks 
when my streamers reached about 60" or so.  So the racing sparks 
on your coil with the larger toroid is understandable.  Those xfmrs
make a nice system.  As a simple cure, you can make a separate
extension coil of the same diameter about 8" tall or so, and just
connect it on top of your existing secondary, and splice the wire.
Then retune the primary outward as needed to tune.  It should work
fine.

cheers,
John


>
> >    Hi everyone.  I'm very new to this, so I have a problem.  I built a
> >6 inch coil using two of the infamous GE copier xfmrs as a power
> >supply.  The coil works well (5 ft streamers), BUT....  I have long, hot
> >sparks running the length of the secondary.  My first secondary for this
> >coil was 6" by 22" with about 1400 turns.  This burned up, since it was
> >badly built.  I just wound a new one which is 6.5" by 28" with 1200-1400
> >turns, and it does the same full secondary arcing.  Coupling doesn't
> >seem to make a difference.  The coil is tuned to the best of my
> >ability.  I just put in a better RF ground, and this seems to agravate
> >the problem.  The only time this arcing does not occur is when the coil
> >is run in moist air, when there is condensation on the secondary.
> >Putting a breakout point on the toroid helps, but won't eliminate the
> >problem.  My toroid is 8" by 22", by the way.  The coil is coated with
> >large amounts of polyurathane varnish, and holds a static charge after
> >each run, if that helps.  Also, these sparks run directly on the
> >secondary's surface.  They punch holes in the varnish with ease.
> >