primary cap

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Thursday, April 02, 1998 10:12 AM
To:  Tesla List
Subject:  Re: primary cap

to: Mike

There was a bit of confusion regarding that paragraph in my book.  If
operated in a pulsed mode you can use a larger cap than the Z match
predicts.  In continuous service such as a neon xmfr it is best to use a
xmfr that equally matches the cap size -- or perhaps just slightly larger. 
The larger size xmfr value provides more current to recharge the cap faster
and will produce longer sparks from most coils due to the "pumping" action
of energy into the already existing large ion field from the previous
streamer.  We seem to have best luck by going 20% larger with a NST than
the Z match requires.  If you are going to a .03 MFD cap I would suggest
you consider a potential xmfr with a suitable current reactor which will
give you a wide range of adjustment over charging current.  A 30 inch spark
from your existing configuration is excellent and it appears you have a
great design.  We use a 30 x 6 inch sec with a .03 MFD cap and 20 x 5
toroid.  With a potential xmfr it produces solid 62 inch sparks running off
a 120 vac mains (it is still portable and doesn't require the 220 which
isn't available in many school classrooms).  We usually adjust the current
reactor for approx 16-18 amp primary draw.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: primary cap
> Date: Wednesday, April 01, 1998 11:23 PM
> ----------
> From:  Hollmike [SMTP:Hollmike-at-aol-dot-com]
> Sent:  Wednesday, April 01, 1998 3:00 PM
> To:  tesla-at-pupman-dot-com
> Subject:  primary cap
> Hi all,
>       I have a question for D.C. Cox, John Couture and any one else who
> to reply.  When I first started building coils(about four years ago),  I
> purchased two books from the ITS museum in Colorado Springs.  The first
> JHC's "Tesla Coil Construction Guide" and the second was DCC's "Modern
> Resonance Transformer Design Theory".  Both of these are great reference
> sources IMHO.  I am glad to find out that both of you are in this
> group.  I now have a question that should be easy for each of you to
>      I am planning to make a modification to my primary cap.  Presently,
I am
> using two 15kV, 30 ma neons to power my coil.  I believe I have
constructed my
> primary gap to be adjustable to about any voltage rating up to about
> Presently, I can get about 36 inch streamers from my setup using a 0.0115
> primary cap, which is great considering I was only expecting about 18 -
> inches when I designed it.  I recently constructed a plate cap, that if
> works as expected, will give me a great deal of latitude in modifying my
> system (I can adjust the capacitance by about 15% by adjusting the torque
> the screws holding it all together).  I can put this new cap in parallel
> the existing cap or use it in place of that cap, and will decide this
based on
> feedback from you.  
>      I have been studying the various design programs on the web and they
> seem to adhere to the impedance matching of the primary cap.  My present
> is a fairly close match due to the fact that I purchased a number of HV
> from a local surplus store and bought all of the ones they had.
>      In DCC's book, it states that due to the short duty cycle the
primary cap
> can be much larger than the impedance match dictates.  In JHC's manual,
> pick the cap size and then size the tranny to be able to power it.  I
> obtained various values for the cap size by working the equation from
> book in reverse and assuming different voltages(RMS, peak, 2X RMS, etc). 
> my first question is which of these values is the one to use?  My best
> is the result that is most conservative(or lowest cap value).  
>      My real question is what would you use for the primary cap in my
> that would provide the best output and yet be safe for the neons.  I have
> chokes and safety gaps in place, so there is no need to remind me of
> these. As is, I can run my coil for thirty minutes without problems so my
> system must be reasonably well built.  I have never seen the safety gap
> so things must be ok as far as I know.  
>      I have tentatively concluded that I could use up to 0.03uF for my
> cap, but wanted to first get advice from those more knowledgable than
> before jumping in.  My main reason for wanting to increase the primary
cap is
> that I just replaced the 4 X 16 toroid with a 6 X 20.  I found that to
> I will have to splice about 1/4 of a turn of tubing to my primary.  This
> wouldn't present a problem, but I would rather increase the capacitance
> reduce the number of turns.  I just want to get some advice before I
> this.
>     Thanks in advance for any suggestions,
> Mike Hollingsworth