Re: [TCML] Caps

[Scott Bogard <sdbogard@xxxxxxxxx>]

Hi Christian.
    My advice, don't concern yourself at all with LTR, you will get a
headache trying to figure it out.  Instead look at this...

sqrt(VA) + sqrt(eJ x BPS x 1.263) = spark length in inches

This is a fairly accurate formula for spark length as related to power
input (VA) *break rate* (BPS) and *capacitor energy* (eJ).  To answer your
question simply, you can use any size cap you please, as long as you can
keep it in tune and match an appropriate break rate.  I like much smaller
than resonate caps, with corresponding higher break rates.  Trouble is
static spark gaps do not usually handle higher break rates as well as
rotary gaps (in my opinion.)  Larger than resonate I think has a bit more
time between spark gap firings and so works well for static gap coils, but
higher breakrate machines usually perform better spark length wise due to
spark growth (as long as you don't go to far.)  Any larger cap than LTR you
will likely need a synchronous rotary to handle well, otherwise firing will
be truely uneven.  By the way, resonate rise can be a good thing, as it in
theorey moves more power faster, BUT it will usually destroy the NST
driving the coil in short order whihc is why you should avoid it.  So to
give you the answer you want, yes you can get away with a much smaller cap,
but to make her sing her best, she is going to want a gap that will give a
high breakrate, I abandoned static gaps for rotaries early so I can't tell
you how to best do that, I'm sure others will chime in!  God luck!

Scott Bogard.

On Wed, Aug 29, 2012 at 2:22 AM, Christian Hill <monolegal@xxxxxxxxx> wrote:

> Hello. I am building my first coil and have a few questions. I read that
> you should stay away from using a resonate sized capacitor as it can cause
> a "condition called resonate rise." Multiple sources say to use a "larger
> that resonate" capacitor to keep this from happening. I've read that you
> can also use a multiple of the LTR capacitance value as well. Let's say
> that the optimum LTR capacitance is 10nF. Since I can double it and use
> 20nF would I also be able to half it and use 5nF? (Assuming that my voltage
> needs were met, of course).
>
> I would assume that the closer I get to the resonate capacitance value, the
> better chances of resonate rise I have. So I should stay as close as
> possible to a multiple of the LTR capacitance, correct? Or should I just
> meet my voltage needs, tune the coil accordingly, and make use of safety
> gaps?
>
> I am asking all of these capacitor questions because I want to get the most
> out of my money. Those Cornell-Dubillier 942C20P15K-F's can really add up
> when you're on a budget. I tried searching through the archives and have
> poured over dozens of tesla coil guides but found nothing that really
> answered my questions. Thank you very much for your help.
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