Re: Position of Secondary WRT Primary - Stupid Question of the day

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

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Bruce,

Tesla list wrote:

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

No problem. This is a coupling adjustment (about a 0.113 coefficient which 
is fine). This can be adjustment for maximum output later.

>   Do I need to pop a
>hole in the plywood to 'lower' the secondary into?

Possibly, yes - if (later) you want to increase coupling by lowering the 
secondary.

>... If so, then how far is adequate?

Up or down and inch or so  (sometimes more, sometimes less). You may not 
need to move it too much. But this isn't your problem.

>   My aspect ratio is around 5:1... I know this is not efficient...

What makes you think a 5:1 h/d is not efficient? This h/d is fine and 
actually recommended by some of the more professional coilers who have 
emperical evidence to rely upon (comparison of what works best for 
difference sized coils).

>can this be 'made up for' by lowering the secondary with respect to the
>primary?

I doubt you could measurement a difference of h/d efficiency in most cases. 
So make up for what?

>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?

Not really. You've obviously aware of the risk and have chosen to go that 
route. Just be careful. You may want to simply put down a metal plate or 
even alluminum foil, chicken wire, etc... to act as a ground plane (it will 
work) and keep your house circuit out of harms way.

>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.

 From the numbers given, it appears your gap is rather narrow. The cap 
(.01uF) takes about 25ms to fully charge to your NST's 21.2kVp value, but 
the total gap distance and electrode size puts it at around 10kVp, thus 
charging the cap to about 46%. This may or may not be the case (appearance 
is often not reality). Did you set the gap to the transformer output 
voltage? It sounds like you may have from the following comments (just my 
curiousity).

>       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?).

None (others may have suggestions).

>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).

Yes, I went to the same school. The cap is fine and sounds well built. 
Should last a long time.

>c.  The Cap, and primary are in series.  This assembly is in parallel with 
>the gap.

Perfect.

>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).

Actually, sounds about right (8 to 9 turns if I got your topload modeled 
correctly).

>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.

Ok, as others have mentioned, slightly large for the coil diameter, but not 
a real big deal. At 517 or so turns, should be ok.

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

This is mostly likely the problem (too big for coil and nst). Why not 
replace the top with a large coffee can for now and tap at about 4.3 turns. 
If you get spark output, you'll know immediately the topload is the area to 
work on. Although, I must admit, I really do like the Washing Machine 
topload! Gotta find a way to keep that on there! Or, maybe keep around for 
a possibly larger and higher powered coil #2.

Take care,
Bart


>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
>
>
>
>