Re: [TCML] Caps

[Futuret <futuret@xxxxxxx>]

Power input (Watts) is the key to TC performance.

I use the formula:

  spark length (inches) = 1.7*sqrt input power (watts)

The formula is for efficient coils.  It's kind of a rule of
thumb, not exact of course because of the many variations
among various coil designs.  

I use a robust 12/30 NST on my TT-42 coil and obtain
42" sparks, using a 4" x 13" spun toroid.  With a typical
12/30 NST it gives about 39" sparks.  I'm using a 1.5nF LTR cap, 
and a 120 bps sync rotary gap.  Using a static gap I obtain
about 38" sparks.  

By the way, an NST can deliver more than it's rated current
in a TC despite being current limited.  This is especially
true if it's fed with 140 volts using a step up type variac,
rather than with just 120 volts.  

If you want to get multiple sparks coming off the toroid, then
you'll need more power for a given toroid size than for
a single streamer.  Sparks can generally push out to
3 or 4 times the toroid diameter, assuming you have
sufficient power for the toroid size.  

John

 

 

 

-----Original Message-----
From: Christian Hill <monolegal@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wed, Aug 29, 2012 8:29 pm
Subject: Re: [TCML] Caps


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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