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

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 4/1/03 7:31:47 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>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


Bruce,

I think you are saying that the bottom turn of the secondary is about .25" 
above the top surface plane of the primary.  That should be fine for 
initial testing.  You may want to lower it a bit after you get it running 
well.  Increasing the coupling will produce longer sparks but that can 
wait.  I usually set mine so the bottom secondary turn is just even with 
the top of the primary.

Your primary sounds just fine.  Your secondary is using much larger wire 
than I would use for this sized form.  With 18" of winding length, you only 
have about 560 turns on the secondary.  You would like around 1000 to 1500 
turns.  # 26 or #28 wire would have been better.

I think your toroid is way too large for the power supply that you are 
using.  I would suggest something like 2" x 10" to start with.  My rough 
calculations indicate the best tune should be around primary turn 7 to 
8.  You should be able to get some sparks out of this coil by laying a wire 
on the toroid so it hangs over the edge then suspending a ground wire a few 
inches away.

You already know about using the house wire ground.  I would suggest using 
a ground plane on the floor like a piece of metal screen or chicken wire 
about 5 feet square and connect the bottom of the secondary to that.

Ed Sonderman