Re: [TCML] Caps

[Scott Bogard <sdbogard@xxxxxxxxx>]

Watts is everything for spark length, you can get the same spark length out
of any voltage current combo as long as it has an efficient gap to
compensate (lower voltage makes gap construction more tricky in my opinion,
up to a point...)  The trick is to balance the cap around the voltage and
current, more current means you need more capacitance to keep breakratesin
check, more voltage means you need less.  Again you can pick any cap value
you like, but as others have said high breakrates are difficult to do for
static gaps, so bigger caps (LTR) is usually recommended.  As a point of
curiosity, what have you actually purchased at this point?  I ask because
you are designing a bit backwards (a mistake I always made) you should pick
first of all, your spark length, or short of that get the most economical
power supply you can and go from there.  I like to do things this way now,
as a smaller coil with big sparks is seriously impressive compared to a big
coil with small sparks.  If Tesla map says you can get 22 inch sparks out
of your transformer, in theory you can get away with 2 inch by 9 inch
secondary wound with 36 awg wire.  Now obviously that would be obnoxious,
but this relationship scales very nicely for larger coils, I was working on
a chart that would give sparks 2.5* the winding length for optimum sized
coils for given wire gages, but I didn't finish it yet...  At any rate,
once you have a power supply, THEN nail down what cap you are using, and
THEN build an appropriate spark gap.  The coils come last, as they are
actually less critical (coil size has little to do with spark length,
provided it is big enough there are not excessive losses, and it does not
arc over.)  For reference, Richard hull reportedly made 10 feet sparks out
of a 13 inch long coil (granted it was a magnifier, but still, that is kind
of ridiculous!)  So yeah, just some food for thought, might want to focus
on sourcing a suitable transformer before doing anything else.  Than again,
everyone has their own method, that is just what I sort of frell into of
late, and it seems to work well.

Scott Bogard.
On Wed, Aug 29, 2012 at 8:13 PM, Christian Hill <monolegal@xxxxxxxxx>wrote:

> I am building a 4.5" (4" inner diameter schedule 40 pvc coil form) by 22.5"
> static spark gap tesla coil. I have 50' of .25"
> copper refrigeration tubing wound into 13.5 turns spaced .25" apart for my
> primary coil. The topload is a 4" ring 16" total diameter toroid. I have
> not decided on the NST yet. I am thinking 12kv 60ma would be sufficient,
> but with a LTR of 21.5nF that's 28 caps I would have to buy. If I buy a
> 15kv 30ma NST that's only 8.6nF of capacitance and about 17 caps I would
> have to buy. I also read in a few of the replies that I can use 1.5x
> LTR capacitance. Meaning I can use 12.9nF (about 11-12 caps) for a 15kv
> 30ma NST, correct?
>
> Quick question: what is most important for arc length? Tesla map uses watts
> to calculate approximate length at 100% efficiency, but in the real world
> do volts or amps have more of an influence on arc length?
>
> Calculations and headaches are not an issue. They were in the beginning,
> when I was doing the math myself, but I have since purchased Tesla map. It
> will just be a basic tesla coil plus a line filter, NST safety gap, and a
> strike rail for now. I plan to do various upgrades such as changing to a
> rotary gap or adding a terry filter in the near future. I am trying to be
> as careful but cheap as possible when building this. I would hate for
> something to blow up and cost me even more money.
>
> As for my expertise, I'm only 17. I have a solid grasp on low voltage
> electronics. While I am new to Tesla coils (and high voltage for that
> matter) I have been doing lots of research and am neither ignorant nor
> impatient. Please do not dumb things down for me, I am good at figuring
> things out and have been just fine with the info given thus far.
>
> Thank you very much for your replies.
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