Re: Capacitance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 1/24/02 8:10:08 PM Pacific Standard Time, tesla-at-pupman-dot-com
writes: 


>
> Hey, 
>
>        How will it affect tesla coil performance if you have significantly 
> more capacitance than is necessary? Will it even work? THanks. 



To whoever wrote this, a name would be nice: 

Many folks seem to be missing the boat about how a Tesla coil actually works. 
I see people starting to build coils that apparently have no idea of the
completed project in mind.  I have said this about a million times now - you
have to do the math first.  There are many spreadsheets out there, including
mine, to make this a relatively easy job.  The size of the capacitor definitely
matters.  The primary and secondary must resonate at the same frequency.  The
exact capacitor value can be selected from a given range for a particular
design by adjusting the primary coil design and tap location accordingly. 
Let's say you have done the math and have decided on a primary of 14 turns and
the spreadsheet says you need a .01 mfd capacitor for the coil to be in tune
when tapped at turn 12.  Now you decide that you want to use a Larger Than
Resonant (LTR) cap and want to use a .02 or .025 mfd cap.  The first thing you
need to do! is recalculate with the new cap value and see where the primary tap
now needs to be.  If it comes out somewhere in the range of less than about 8
or 10 turns, then I would think about what else could be changed to lower the
secondary frequency (larger toroid maybe) so more turns can be used in the
primary.  I like to use 10 or 12 turns minimum.  You get more primary
inductance, lower spark gap losses (lower primary current) and better
performance. 

The whole thing must be looked at as a system where once designed, changing any
one component will require changes in other areas to maintain performance (say
proper tuning).  If you calculate that you need a .01 mfd cap, you can probably
make minor changes to allow you to use maybe a .005 mfd cap or maybe up to a
.025 mfd cap -- buy you cannot use say a cap that is 10 times larger, for
example a .10 mfd cap. 

Ed Sonderman