Re: BEGINNER PLANS FOR SCIENCE PROJECT PLEASE HELP

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

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

Here we go with all the opinion stuff... I'd really, really recommend
against the carriage bolt needle gap (ends of the bolts are the gap) or
hemisphere gap (heads of the bolt) approach, and advocate the "3 copper
tube" gap.  The cost is about the same.

a) The point on the needle gap gets very hot very quickly, radically
changing the spark gap characteristics.  This makes tuning a problem,
because as the coil goes into and out of tune, the current through the gap
changes, changing the heating, changing the timing relative to the AC
charging cycle, etc.

b) Thermally, it's hard to cool the needle gap, because the entire heat flow
path is through the bolt, and steel just isn't all that wonderful a
conductor, either electrical or thermal. It also doesn't have much surface
area.

c) You've got to figure out some sort of wire lugs to attach the wires to
the gap terminals either way.

d) Adjusting the needle gap is a pain.  You have to have two nuts on each
bolt, some sort of thing to stick the bolt through (usually an angle bracket
or a piece of plastic. If you use plastic, there's the "melting support"
problem.

e) Most hardware store bolts (unless you use brass carriage bolts, which are
hard to find in bigger (1/4" and up) sizes) are plated with either Cadmium
or Zinc, both of which are toxic and will be vaporized by the spark.  To get
a reasonable gap size with this approach, you're looking at 1/4" carriage
bolts minimum, and probably something like 3/8".

---
with a 3 copper tube gap, the spark area is spread over the entire length of
the tube, so you're less likely to get little redhot spots
with a 3 copper tube gap, two of the tubes (which the wires are connected
to) can be permanently attached and don't ever need to move. All the
adjustment is done with the third tube
It's very easy to make a cooled/blown 3 tube gap, which greatly improves
performance, even on a small NST powered coil

On my 15/30 powered coil, changing from a bolt head gap to copper pipe
dramatically improved performance, and adding a small muffin fan to blow
over the pipes also greatly improved performance.

Arrange the tubes in a triangle (axes of tube parallel)
A      B
O      O
      O
      C

A and B are bolted down, and have the two HV wires attached.  C is the
adjustable one.  There are lots of ways to attach them, but a bolt through
the length, with a suitable washer over the end, works very nicely.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, November 19, 2003 7:36 PM
Subject: Re: BEGINNER PLANS FOR SCIENCE PROJECT PLEASE HELP


 > Original poster: "Laurence Davis" <meknar-at-hotmail-dot-com>
 >
 > Ravi,
 >    the multi-gap spark gap designs are helpful for performance for medium
 > to larger coils,
 > but you can also build a simple single point gap.  It won't perform as
 > well, but still provides the
 > function of a spark gap.  A single point gap can be as simple as two
 > carriage bolts mounted on L brackets.
 >
 > I'm sure you've read the tesla safety faq's, but do so if you haven't.  It
 > hasn't been mentioned,
 > but remember the spark gap is comparable to a welders spark, which means
 > DON'T look directly
 > at it.  Use a welding shield from a mask and you can get these separately.
 > Even if you know
 > the safety issue here, kids and teachers in your class may
 > not.  Electricity can be fun, but blindness
 > is not.
 >
 > be safe.
 >
 > just my 2 cents.
 > larry.
 >
 > _
 >
 >