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Burned Secondary...




From: 	Dan Kline[SMTP:ntesla-at-ntesla.csd.sc.edu]
Reply To: 	ntesla-at-ntesla.csd.sc.edu
Sent: 	Monday, September 08, 1997 10:58 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Burned Secondary...

Hi all,

I made a couple of changes to my system the other day and promptly had
several turns weld together on the bottom 1/3 of the secondary. I cut that
part off, retuned, and had the rest of the secondary burn the same way. I
don't mind this though...Last time I jumped up a level in coiling, it was
because I was burning secondaries (arcing through the inside of the form),
but it's not that way this time. Here's the system before the changes:

Power Supply:  14,400V, 1.5kVA Distribution xformer
Current-limit: approx 750W space-heater 
Primary cap:   .025 uF  20kV Plastic Cap brand
Gap:           3 series gaps
Primary:       16 turns #6 rubber-covered, stranded cable in saucer-shape at 
               15 degrees, 3/8" spacing, tapped at about turn 11
Secondary:     6.25" lucite form wound 22" with #22 double-covered formovar
               magnet-wire
Discharger:    2 toroids stacked, Al dryer ducting, both 24" x 4"
Performance:   Occasional 36" strikes, double and triple forked, blue-red
in                               color

Replaced the 3 series gaps with 4 electrodes on an 8" lexan disc, 3300 rpm
motor, but worked best at about 1700 RPM

Replaced the space heater with the primary of a microwave-oven xformer.

Everything else was left the same.

Performance: White bolts all over the place, like being inside a
thundercloud. Assistant screaming in fear and awe ;)  Bolts too long for
room, but no strikes to the system itself. Assistant heading for bathroom,
soon to make ten-foot-pole for flipping main system-switch ;) After
shutting down, the system wouldn't run again, due to shorted turns on
secondary. 

I never saw any inter-turn arcing, but pin-point hot-spots shorted the
secondary turns in several places.

So I'll wind an identical secondary soon, but before I do, I'd like to know
what burned me up. :)  I can guess over-coupling, so I've purchased 1/4"
copper tubing to make a flat-pancake primary, spacing 1/4" if it's over
coupling.

Another thing is that, before we replaced the space-heater with the
microwave xformer primary, the coil ran as it had before I replaced the
static gaps with the rotary, with only a slight improvement in performance.
But I kept hearing this whummmm-whummmm-whummmm sound that I thought might
be a beat frequency or some sort of phasing response. Coil-performance
seemed unaffected by it, however.

The real destruction and performance-increase took place when the ballast
was changed to the microwave xformer primary.

Running the distribution xformer without ballast promptly blew
circuit-breakers, btw :)

So. Any ideas what caused the shorting on the secondary? Again, these were
pinpoint-hotspots and were *not* caused by arcing across the secondary from
one turn to another.

Thanks,

Dan