Re: Newbie with questions...

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

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, September 09, 2003 9:00 PM
Subject: Newbie with questions...


 > Original poster: The MCP <ejkeever-at-comcast-dot-net>
 >
 > Hello, everyone. I just signed up and have some questions to ask about
some
 > aspects of coiling.
 >
 > I've built a small (tabletop-size) tesla coil for fun, and I am observing
some
 > very odd behavior from it. But first, I should provide some basic info.
 >
 > The secondary is a .75" PVC pipe (I got excited and built it before doing
 > enough research), with about 10.5 inches of 32 gauge magnet wire on it,
about
 > 1000 turns. The helical primary is 5 inches in diameter, ~3.5 inches tall,
 > with 5 turns.

Might scrounge around and wind a new secondary... something like a 2"
mailing tube with slightly larger wire might be a nice improvement.. Maybe
the cardboard tube from a roll of paper towels? Fed Ex used to have free
mailing tubes for shipping in about 2-3" diameter.

 >
 > The main tank circuit has a smallish 5000/20 NST and currently a single
 > 40KV/2nF cap from TDK that I picked up for $30.

100W input -> 17" sparks under ideal circumstances... how big a sparks are
you getting?  10 inches or so?
2nF should be ok    Ball parking it, 20 mA into 2 nF gets to 7 kV many times
per half cycle (8.3 ms)
1 Amp->1uF -> 1kV in 1 msec
20 mA->1 uF -> 20 V in 1 msec
20 mA-> 1nF -> 20 kV in 1 msec
20 mA-> 2 nF -> 7kV in 0.7  msec

In reality, you can't get the full 20 mA out of your NST, so you're probably
reasonably close... Going to 6-8 nF might improve things, but might also
kill the NST from resonant rise if you get a misfire (put in a safety gap!).
You could test by building some beer bottle caps (quick easy, and you might
have some friends to help you empty the beer bottles) to change the C for
testing... If it works much better with bigger C, then fork out the next $30
chunk, etc..

 >
 > The spark gap is a simple static gap, currently separated by about .125
 > inches, using the tips of a pair of screws. When these wear out, I can
just
 > replace them with fresh ones. The gap can be set for up to 1/2 or so inch
 > separation.

you might try turning the screws around and using the heads as the gap
electrodes... Or a pair of carriage bolts.. or, a couple pieces of copper
pipe (3/4" sweat on couplings are nice)... Tiny electrode ends lead to hot
electrode ends leads to firing "too soon"...

 >
 > Currently, the whole thing is in a highly experimental state. By that I
mean
 > that very little is set in stone; Almost all the major connections are
either
 > twisted together or clipped. So you've got a lot of latitude to change
 > things.
 >
 > Anyway, on to my questions. First of all, I'm wondering if I've got any of
the
 > components grossly off-key. Comment away.
 >
 > Second, I've found something odd( to me at least). One day, just for the
heck
 > of it, I took off the topload and stretched the wire straight out. Nothing
 > much happened. But when I took the 6 inches or so of wire and wound them
into
 > a small spiral (about 7 turns, 3/8 inch diameter, 1 inch long), the coil
 > worked almost as well as with the big copper topload so I abandoned it.
Can
 > someone tell me why?

With such a small coil, the coil of wire acted as your top load.  The
contribution to the system C of the top load was quite small either way, so
the tuning will be approximately the same. The effective radius of curvature
(which determines the voltage before breakout) was probably about the same
either way.


 >
 > Thanks for taking the time to slog through all this and answer my probably
 > silly questions!

Experiment, Experiment, Experiment....

 >
 >