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Re: Continued Problems (fwd)



---------- Forwarded message ----------
Date: Sun, 3 May 1998 13:00:40 -0400 (EDT)
From: fxphoto <fxphoto-at-centuryinter-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Continued Problems (fwd)

 Let me preface this by stating that I am a relative "newbie" and I have not
worked with a pole pig yet, so it could be my lack of understanding causing
your cap to stand out like a sore thumb to me. You state that you are using
a 0.025 uF 15kv (A.C. or D.C. rating?) cap in conjuction with a 5kva 14,400
volt pole pig. 
 My understanding states that 14,400 (eff) x 1.414 (pk) x 2 (pk to pk)
would equal 40,723 volts peak to peak and when tossed into a coil, the
returned peaks would greatly exceed even this.
 Mike Hammer has stated that above 12kv you should use three caps in series
in oorder to limit the high voltage strain across each individual cap. I am
just starting to understand why.
 I believe at 5kva, you are putting out around 0.347 A -at- 14400 volts which
would need a total capacitance of around 0.064 uf at about a 60kvdc rating.
 I am sorry that I do not understand the effect of the current control
method that you are using has on Xc but it seems that Xc would change as you
change the current output. If this is so, the capacitance would need to
change according to the current output. Perhaps someone can jump in and
explain this to me.
 Your 0.025 uf cap should work best at a current output of 0.140 amps , or a
little less than half of your full 5kva output.
 Your safety gap is firing when the voltage reaches the breakdown voltage of
the gap. I am not sure what 5/8" is voltage wise, but if someone said use
5/8" I would stick with it. By increasing the capacitance, you can increase
the current throughput without changing the voltage (i.e. causing the safety
gap to fire).
 Just my semi-informed 2 cents!!             Bill Turbett

P.S. I do not know what you are spending on commercial caps, but if it is
anywhere near the prices I have seen you would be better off building your own.
If you are interested in building your own or in having one built, I am
presently designing an easily made, modular and variable capacitor
specifically for tesla coils. email me directly ( Fxphoto-at-centuryinter-dot-net )
for details as I would rather not make an untested design public.


>>Date: Wed, 29 Apr 1998 12:52:12 EDT
>>From: Esondrmn <Esondrmn-at-aol-dot-com>
>>To: tesla-at-pupman-dot-com
>>Subject: Continued Problems
>>
>>Sorry, this is going to be a long one.
>>
>>I fired up my 6" coil last night for the first time this year.  I am still
>>having problems.
>>
>>Quick overview: Secondary 6" dia, 991 turns of #22 awg, 29.1 mh.  Primary 3/8"
>>copper tubing wound in a 30 degree saucer shape, 3/8" spacing between turns,
>>I.D. 8", O.D. 26",  5.25" tall, 14 turns total, 88 uh.  Secondary is mounted
>>so the lowest turn is  3.5" up from the first turn of the primary - right at
>>about turn 7 or 8.  Mark Rzeszotarski (sure hope I got that right Mark)
>>calculated the coupling to be about .167, so I wouldn't think it is coupled
>>too tightly.  Best tune is at turn 11.75 with a 5" x 40" toroid.
>>
>>Capacitor is a .025 uf, 15 kv Condenser Products unit with a spark gap mounted
>>directly across it made of #10 solid copper wire with 1.0" dia loops on the
>>ends.  Gap is set to 5/8".  Power is from a 5 kva 14.4 kv pole pig and is
>>supplied across the spark gap which consists of a rotary with a static gap in
>>series with it.  Current is limited to the pole pig via a Miller Thunderbolt
>>welder with an adjustable resistor stack in series with the welder.
>>
>>I built this coil about two years ago and scaled things up gradually from neon
>>sign transformer to the pole pig.  I was quite happy with the performance,
>>getting nice white hot bolts up to 80" long at about 8 kva input.  Then the
>>first C. P. cap blew up.  I replaced it and within not too long, lost the
>>second one.  Several folks on this list suggested I install a spark gap across
>>the cap unless I have lots of money - which I don't so I did.  Now, I can't
>>input much power without firing the cap safety gap.  Last fall, last time I
>>had this coil fired up, Malcolm, Dr. Cox and a few other helpful folks
>>suggested I had a bad case of 60 hz resonance.  I have to ask a question here
>>- are there systems out there that can be run at say 10 kva with 15 kv in and
>>not fire a .25" safety gap across the cap?