RE: Many questions

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

Original poster: "Matt Morrissette by way of Terry Fritz <twftesla-at-qwest-dot-net>" <yinzara-at-MIT.EDU>

Ok, well I've redone my calculations.  I also have a new transformer
because the old one doesn't work. The new transformer is 12kV 60mA.  I
also am going to use the Geek Group MMC capacitors. I'm going to use 8
of them in series to make .0199uF.  I redid the calculations using the
same secondary coil and toroid. Turns out I was measuring the toroid
wrong and it's 24" from center of the tube to center of the tube and 6"
diameter tube.  I redid the calculations with the JavaTC and it says
around 17 1/3 turns are needed to hit the 187.24khz frequency that the
top coil is resonating at.  I will put the primary about 3 inches below
the secondary. I'm going to run the coil outside so that I get basically
no external capacitance.  WinTesla gave some different numbers but they
didn't make as much sense as the JavaTC. Does this coil sound
reasonable?

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent: Tuesday, October 08, 2002 9:59 AM
To: tesla-at-pupman-dot-com
Subject: Re: Many questions

Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Jeremy,

The transformer is small for trying to charge a 0.3uF cap size. That
would
be considered "huge" and would
be better sized for large coils ( >18"diam.). Also, JavaTC recommends
running E-Tesla6 to take into account
external capacitances which directly affect the system and the tuning.
In
your case, your coil frequency
(in a typical garage) should be around 207kHz with the toroid placed on
the
coil where the bottom plane is
even with the top of the secondary and the coil itself about 20" off the
groundplane. This changes the
secondary resonant frequency and the primary must be tuned accordingly.

If for some reason you tried the .3uF cap, then yes, you would need to
tune
to about 3.4 turns to hit
207kHz. However, you may never get that cap charged up. If it did, you
may
not want to be around when it
discharged (67 joules = BANG!). Would be very dangerous, loud, and
destructive.

Now, lets say you want a cap size that your transformer can charge
reliably
without difficulty, then you'll
need something around 0.005uF - 0.0075uF. Since 0.005uF is resonant, you
may want to move to .075uF. But
guess what, although the cap would be in the ball park, your helical
primary would be 3 x taller than your
secondary since you would need about 80 turns on it. The fix here is to
drastically reduce the large
spacing between turns.

Say we move to 1/4 inch spacing (ball park). We then reduce the turns to
near 25. Now your almost ready to
spark, but coupling is pretty high at 0.24. So to get it down say to
0.15ish, raise the secondary up 3"
from bottom primary turn. This will get you about 0.157.

I'd like to say "your ready to spark", but there are other tid bits. For
now, I would recommend wondering
around some Tesla Coil web sites looking for similar component values.
Try
to take a look at what some
other's in your power supply range have built (that works well). Some
things worth looking at is the h/d
ratio (my coils stay between 4 and 5), the type of primary best suited
for
the coil, and the cap size they
are charging with their transformer.

Take care,
Bart


Tesla list wrote:

> Original poster: "Jeremy Neuringer by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jneuringer-at-hotmail-dot-com>
>
> I m a new coiler and have done a great deal of research to design the
coil I m
> currently implementing.  I ll give all the specs and then ask the
questions.
> (please keep in mind the only part actually built is the primary, the
rest can
> possibly be changed by recommendation) The coil transformer is a 15kV
450VA
> 30mA 60hz output neon light transformer. The capacitor is a 25kV .3uF
box
> capacitor I bought off ebay.  The primary is 7 diameter 6 gauge copper
wire
> wound in a helix with 4.17 turns and approx 1.2 space between
windings.  The
> secondary is 21AWG enameled magnet wire 1395ft wound on a 4.25
diameter pvc
> pipe 39 tall.  It is tuned to approximately 177kHz. The top load is a
30
x6.25
> toroid.  The spark gap is a collection of 10-½ copper pipes (1.5 in
length)
> screwed to a piece of plexiglass with around .025 gap between each and
a fan
> blown over the top.  I got all these calculations by playing with the
TC java
> tesla designer. However I m not sure if this is going to work
correctly.  The
> low amount of turns on the primary seems odd to me (I know if I use
the
> recommended .066uF capacitor (by another java designer) it says to
wind 18
> turns).
>
>
>
> Questions:
>
>
>
> Do you feel this should work?
>
> What wire should I use to connect it all together and what type of
connectors?
> I bought high voltage wire but it doesn t handle much current.
>
> Is the spark gap appropriate?
>
> What type of safety gap should I use?
>
> How can I discharge the capacitor so I can work on the coil safely? I
think
> shorting it would damage it. What can I use for a resistor to
discharge
it more
> slowly?
>
> How and where should I ground it?
>
> Should I put a piece of Styrofoam in the inner part of the toroid and
cover it
> with aluminum tape?
>
> How should I connect the toroid to the top of the coil and should I
leave
some
> blank pvc before the toroid?
>
> What do you recommend I use to coat the secondary?
>
> If you could change something on this coil, what would you change?
>
>
>
> Thanks for all your help,
>
>
>
> Matthew Morrissette
>
> MIT frat boy Sophomore in Comp Sci and EE looking for fun with a tesla
coil