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Jacobs Ladder style spark gap



Original poster: "Ryan Molecke by way of Terry Fritz <teslalist-at-qwest-dot-net>" <ryan-at-molecke-dot-com>

Hi all,

     I just got my first coil arcing, woohoo! I'm sure I'll seek suggestions
sometime soon on various components, since I'm addicted now.

     I am using 9000V at 30mA across a (approx) 2.5 nF capacitor. I run
straight from the NST to the cap in parallel, which is most likely bad but
I'll put some chokes on later. Anyhow,
I was going to make a Richard Quick style spark gap, but then I just went
with two of the little copper tube peices, 1/2" diameter I think, around 1"
long, with holes drilled in them for screw fittings. I set the two peices of
tubing so that they were in a very slight V formation laike a jacobs ladder,
with the bottom spacing being variable.
     Now when the spark jumps across this gap it jumps all over the copper
tubing, going from top to bottom erratically, which seems to help keep it
more quenched. It is not really like a jacobs ladder, but then again it is!
I'm sure it generates a ton of interference, LOL!
Maybe I'll put the peices together for a Quick style gap and see if I get
more arcing...

Ryan Molecke



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, April 01, 2003 6:26 PM
To: tesla-at-pupman-dot-com
Subject: RE: Position of Secondary WRT Primary - Stupid Question of the
day


Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<Gary.Lau-at-hp-dot-com>

Hi Bruce:

Your secondary starting 1/4" above the plane of the primary is quite
typical.  This distance determines the primary to secondary coupling.  Too
little coupling will diminish performance, but it won't kill it outright.

A 5:1 aspect ratio is also quite typical.

For a 3.5" secondary, 20 gauge wire is on the thick side.  Heavy wire by
itself is not bad, but it limits the number or turns you can wind in a
given length.  I calculate that you have about 520 turns.  1000-1500 turns
of #26 or so is more typical.  But yours should still work to some degree.

The integrity of your RF ground won't affect performance too much, but it
will affect how much HV & HF garbage gets into your power mains.  I get by
using my 3rd wire ground for my mini coil; it's not clear just where to
draw the line and use a dedicated RF ground.

Your gap sounds fine, as does your cap.  You may have a problem using 1/4W
bleeder resistors, 1/2W units are typically used and will hold off a higher
voltage without arcing over.

I'm not familiar with a "'Washing Machine' Toroid".  Are you using the
steel tub (not a "toroid") from inside a washing machine?  If so, this may
be too large, and I wouldn't know how to calculate its top-load capacitance.

Are you sure that your primary & secondary are in tune?  Not understanding
your top load I couldn't complete the calculations.

Regards, Gary Lau
MA, USA



Original poster: "Bruce Boettjer by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <bruceb75-at-cox-dot-net>


Hello,

In just a couple of months of subscription to this list, I have amassed a
wealth of knowledge... Someone should publish this stuff!

I have just completed a small system, but am having no luck getting any
spark, or even glow.


There are some specific 'failure points' I think are present, but am unsure
about, due to my lack of experience.  I would appreciate any response...

1.  The secondary sits on the primary's plywood base in such a way the the
windings appear to not match up.  Stated differently, the primary is a
uniform 0.75" from the surface of the plywood.  The secondary winding does
not start until 1" from the plywood.  Is this a problem?  Do I need to pop a
hole in the plywood to 'lower' the secondary into?... If so, then how far is
adequate?  My aspect ratio is around 5:1... I know this is not efficient...
can this be 'made up for' by lowering the secondary with respect to the
primary?

2.  For initial testing, I have been wanting to work indoors (my 10' copper
pipe that is driven into the ground is in the backyard...).  This has
prompted me to live a little dangerously by connecting the bottom conductor
of the secondary winding to the green 'ground' that runs through my house
and goes to each and every AC outlet.  While I understand the potential
personal risks beforehand, and have taken adequate prophylactic (that's such
a great word!) measures, there is still no joy... Is there a problem with
this method, other than the obvious RF burn hazard?

I was hoping that those much more knowledgable than I could take a look at
this system and tell me where I went non-linear...

The system is comprised of:
1.  15KV x 30mA NST.

2.  Homebrew Richard Quick style stationalry spark gap
	a.  10 pieces of 5/8" copper pipe, 4" long.
	b.  .010" to .020" spacing(.010" feeler will pass through, .020" will not).
         c.  Sealed wooden box with a wafer fan (110V AC) sucking air.
         d.  Spark Gap is in parallel with transformer.

         i.  With no Cap, there is much noise and light from this gap.
         ii. With Cap, there is much more impressive noise and light from
this
gap.
         iii. I can see static on my neighbors TV when I run this thing (Any
easy suggestions for                          isolation?).

3.  MMC Cap comprised of 15 'Geek Group' 0.15uF -at- 2KV caps in series (1
string)
	a.  Being a graduate of the "Ouch! Electricity really hurts 'school'", I
strongly believe in safety as a design practice, not as an afterthought -
therefore, each cap has a 10M Ohm, 1/4W resistor in parallel with each cap
(so much for the soap-box).
         b.  A 30KV cap that has more capicitance (overrated) is much better
and potentially longer lasting than a cap that has just enough capicity for
the task at hand (IMHO, please correct me if I'm wrong).
         c.  The Cap, and primary are in series.  This assembly is in
parallel
with the gap.

4.  Primary Coil
	a.  ID of 6"
	b.  13 turns of 1/4" copper tubing, spaced 1/4" apart (holes in keepers are
0.50" apart).
         c.  Flat, pancake style.
         d.  I 'machined' keepers out of a plastic cutting board.  There are
five keepers, bolted down with 6/32 nylon screws in a circle, to a 3'
diameter piece of plywood.
         e.  There is no ground 'strike-rail', yet.
         f.  The center of the coil is connected to the gap.
         g.  The 'tap' is connected to the cap.

	i.  The math says that the tap should be around 9 turns (and some change).

5.  Secondary Coil
	a.  e-bay special
         b.  3.550" PVC, 20" long
	c.  18" of 20 gage wire, with a nice coating
         d.  winding starts 1" from each end.

6.  'Washing Machine' Toroid, 24" OD, covered in Aluminum tape.

Continuity checks performed with a multimeter show a good circuit through
secondary and toroid, as well as good primary circuit connections (Crimp
terminals and alligator clips, all with soldered conenctions).

For those who have made it this far into this increasingly verbose post(I
really didn't plan it this way), Thanks!  I really would appreciate any
feedback or stories that may help.

Regards,

Bruce Boettjer
Oceanside, California