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Re: Burned Secondary...




From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Saturday, September 13, 1997 7:27 PM
To: 	Tesla List
Subject: 	Re: Burned Secondary...

At 03:52 AM 9/9/97 +0000, you wrote:
>
>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
>
--------------------------------------------------  snip

>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

-------------------------------------------------------------------

  Dan -

   I ran the parameters of your coil on the JHCTES program with the
following results. There are actually 34 program outputs.

  Primary inductance            60.74 uh  (11 turns)
  Primary capacitor               .025 uf 
  Secondary inductance     27.48 mh  (800 turns)
  Sec self capacitance         10.35 pf  (6.25 x 22)
  Toroid total capacitance  45 pf
  K factor                                    .20

  The above program outputs are in tune at 129 KHZ according to the equations 
     LpCp = LsCs   and    F = 1/(6.283 sq rt (LC))
     Cs equals the self capacitance of the coil plus the capacitance of the
toroids.

  I doubt, however, that your two toroids equal 45 pf so it appears your
coil is not in tune. Note that when your transformer is short circuited
(Tesla coil operation) by the spark gap it can produce as much as 15 KVA (10
times rating). The type of ballasting will determine how much KVA input is
going into the Tesla coil system.  Being out of tune and overpowered could
cause your burnouts. Your coil could be put in tune by changing any of the
Lp,Cp,Ls,Cs parameters and a simple computer program can help you to make
the changes.

   John Couture