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Re: Optimum couping? - was: Baffles

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi David,

I think I get what D.C. is doing here, he's implementing a recommendation that will give the biggest bang without the troublesome racing sparks or flashovers.

There is certainly a primary to secondary clearance of 1.5" assumed (or at least near that). That is something coilers should keep in mind when designing their primary's for these coils. The proximity of coils is key to coupling, and with a given sec ht recommendation, the primary proximity should also be identified because it is the reference point for the running conditions of the system recommended.

I run a moderate k. I've adjusted the primary to suit a sec bottom turn at the same plane as the primary on my small 4.5" coil which also uses a 1.5" clearance. It runs smooth driven by a 12/60 NST for the first minute, but if I let it continue on, it does get a racing spark now and then (not often, but periodically on long runs). So, I guess I keep my coils on that edge.

Take care,

Tesla list wrote:

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi Bart, D.C., all,

I too have  been reading the Dr.'s "rule of thumb" statements
about the primary/secondary coupling. I realize that D.C. has
probably forgotten more about coil building than most of us
will ever learn, (that's a complement, DR :^) but from my limited
personal experience, it seems that the verticle height of the secondary
above the plane of the primary spiral that the good doctor prescribes
leaves for very loose coupling and poor power transfer. Case in point:
With my Green Monster coil: http://dawntreader.net/hvgroup/david/gm.html
I originally placed the lowest turn of the secondary about 6" to 7"
above the horizontal plane of the flat, spiraled copper
tubing primary coil. Since my secondary is 12.5" in diameter,
according to Dr. Resonance, the lowest winding of the secon-
dary coil should be about 7" to 9"? above the horizontal plane
of the primary coil. When I fired it originally with the 6" to 7"
clearance, it would only produce 6 to 7 ft arcs, maybe an occa-
sional 8 footer from a 15 kVA pig. Once I "tightened" the coupling
and brought "down" the secondary to where the lowest turn was
only about 1.5" to 2" above the plane of the primary coil, the output
dramatically increase to 10 to 12 ft sparks (with an occasional 14 ft
strike) and the sparks were also considerably brighter. The 15 kVA
power source as well as all other aspects of the system remained
unchanged. And I did NOT incur racing sparks by "adjusting" the
coupling. What did cause me to start getting racing sparks was
firing it off outdoors under very windy conditions where the stream-
ers were "blown" back into the side of the secondary coil. This
also burned out my 18 kV rated distribution arrestor and caused
worrisome flashovers along the primary coil that were not previously
a problem. I had to recoat the secondary with multiple coats of spar
urethane varnish to repair the spark damage to the surface of the
secondary but did get it to running right, for the most part, again.

Anyway, I think Bart does raise a good point about how large the
diameter of the innermost turn of the primary is in relation to the
diameter of the secondary. That would definitely make a difference
in the coupling. Maybe others can offer their input into this matter
as to why I seem to get a discrepency in the optimal coupling of
my coils vs. Dr. Resonance's suggested coupling coefficients? I
have seen pics of D.C.'s large coils from the Teslathon photos and
it's obvious that he does subscribe to the very loosely coupled
primary/secondary coil configurations and yet he does get some
very impressive output spark lengths vs power levels.? What am I
missing here?

David Rieben

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, April 26, 2006 7:57 PM
Subject: Re: Baffles

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi D.C.,

I've noticed you have mentioned in recent
postings specific sec winding locations above the
primary plane as based on the coil diameter. In
this particular post, you suggested 2.25" above.
I understand you have made many coils and have
experimentally determined this information. But,
you must also assume a specific primary
dimension. For example, if a coiler through zero
experience made the inner primary diameter 8" to
be used with a 4" coil, well then you would
greatly affect L1 to L2 proximity (k). So, in the
case of coil Rich is building, what dimension would you recommend?

Take care,

Tesla list wrote:

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>

If you plan to produce a spark length equal to or greater than the coil length then use baffles to preclude any chance of interior flashover. No vents in these baffles as they need to be 1/4 inch thick insulation.

There is no need to make your sec height adjustable. I've fully explored this years ago. Just start the sec winding at a location that will be 2.25 inches above the even plane of the primary and you will have the best spark with no racing spark problems. Wind your coil with #26 AWG wire and use a height/OD ratio of 5:1 for a nice coil.

Dr. Resonance
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, April 25, 2006 4:27 PM
Subject: Baffles

Original poster: "Rich" <rdjmgmt@xxxxxxxxxx>

I am getting ready to build my next coil.
Secondary form is 6 id drain pipe. I just
completed a winder setup (and yes it will be left
to right). It has two brush coats of polyurethane
on the out side it and now is setting on end with
a 100w bulb in it to make sure it is dry before I
spray the inside. A note a few days ago Dr. R
said to be sure and install a baffle about 5"
inside the tube and seal with RTV.  I have a 6mm
Lexan plug at the top for torrid mount with a ¼
hole in it and a Lexan plug backed up by a Lexan
plate at the bottom, both vented, so I can mount
the secondary with nylon threaded stock to adjust
height if needed.  This assembly will slide down
through the plywood that the primary is mounted
on. The primary is above the plywood by 1.5"
 Do I still need the baffles about 5 "inside the
tube and should they be vented in the center?

Rich, from the middle of Missouri