# Re: [TCML] How close is close enough? (Primary capacitance)

``` Brandon,

Not critical at all.  In many tests I've used for example double
or half the normal capacitance, and it didn't make much difference
provided I had enough turns on the primary to tune again properly.
Of course with NST's you want to avoid running near resonance of
the NST.  With pig power there's a lot of leeway for capacitor size.
Of course with much smaller capacitors, you'll need to use a higher
break rate.  So if you're using a rotary gap, that has be to
considered.  A static gap will self-adjust the break rate to some
degree based on capacitor value.  To really get the optimal
performance from an NST the cap has to be somewhat close
to the optimal LTR value, but we're talking much more at 10%
than 1%.  Of course tuning must always be optimized in all
cases.   I've generally found best results when I optimized my
cap size for 120 bps operation and the desired input power level.

John

-----Original Message-----
From: Brandon Garretson <garretsontech@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, Mar 23, 2010 10:33 am
Subject: [TCML] How close is close enough? (Primary capacitance)

Greetings TCML,
My question today is regarding primary capacitance and how much
headroom we have to play with while still achieving close to maximum
performance.
Between being a bit of a noob and more than mildly math-tarded, I tend
to rely on programs to do the math for me as well as searching this
incredible forum for posts from people who have encountered similar
problems. But what I have not been able to deduce thus far is this;
How close is “close enough”?
I feel that Telsamap and JavaTC are very helpful applications
(although they don’t always seem to agree which makes things even more
confusing). They give you very specific data as to what the primary
capacitance should be in any given tank circuit, not a narrow range,
but a seamingly dead-on set in stone number.
In an ideal world, we could nail that number every time. But since we
(I) live in a much less than ideal world (the real one), some of us
(myself) are required to work with what we have.
The core of my question is this, how many nf away from the ideal
capacitance can one go before he can no longer compensate through
tuning and still achieve good, if not excellent, performance?
Im sure the amount of leeway would be different depending on the size
and design of the apparatus so let us say we are talking about fairly
conventional, medium sized, NST powered RSG devices.
To give a specific example, lets say the design on paper demands 17nf
but your cap is 20, same design with a different transformer, it wants
35nf and the cap you have is only 33.
Are a few nf in either direction going to noticeably impede performance?
If one had to choose a less than perfect capacitance is it better to
go bigger or smaller?
Is there a certain percentage, in general, of the ideal capacitance
from which one can deviate were any slight decrease in performance
would go unnoticed? Say +/- 10%, or would it be closer to +/- 1%?

Thanks!
Brandon, NJ
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