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Re: Its working <VBG>



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In a message dated 97-03-12 00:18:38 EST, you write:

<< 
 Hi folks,
            well after all the trials and tribulations I have eventually got
 the coil working.  The answer was, of course, the capacitor.  I eventually
 tracked down the materials and got a half decent (two actually) cap built
 and soaked.
 
 This evening I have had the beastie working well and have 18 inches of spark
 from same.  OK, sit down, take a deep breath or two, maybe have a cup of
 coffee or stronger.  No big deal for this list maybe - but a very big deal
 for me.  However, now that the beastie is going reasonably (well) it
 actually poses many more questions than when it was just a mess of copper
 and wire on some crappy plastic framing and wood stock.
 
 Specifically :
 
 Let me first start with what is running:
 
 15000/60ma Neon
 
 Quick gap using 1 inch copper pipe and 13 divisions -at- .028 inch gap each
 
 Primary - Vertical 8 inch diameter 1.25 gap 9 turns tapped at 9
 
 Secondary - 26 inch wound 2.25 inch poly pipe on varnish wound at 51 turns /
 inch (I think I am using 24 gauge ? - but I don't know exactly as it was
 brought as scrap)
 Earth is  8 ft of 5/8 copper rod driven into wet clay.
 
 8 x 3 inch torroid made of scrap plastic (with wire winding) exhaust ducting
 from the tumble dryer covered in foil and thick aluminium sticky tape (bodge
 tape).  None to smooth but the correct shape at least.
 
 Caps -  I calculate my caps at 0.0105 uf using the Tesla software by Walt
 Noon - circa 1993.  They are 450mm by 1800mm AL foil and 1.5 cm (sorry we
 are metric here now) by 500 x 2000mm  low density polyethelyne sheet.  All
 rolled tight and placed in 6 inch (150mm) plastic drainage pipe.  The fluid
 is pure mineral oil.
 This evening I had the caps in series and the all the gaps firing (I have a
 jumper system on my gaps that allows me to select 2-13 gaps as required).
 
 I started at 2 gaps and nothing happened, but you could see some small
 corona around the top.  However this was to break in the caps (they have
 been soaking for a week - 10 days) so no problem. After a few minutes
 without cap stress I opened up the gaps.  As the gaps increased so did the
 spark.  Initially I did not have the toroid on, just a 3 inch copper nail
 that forms the top of the secondary.  By gap 9 there was a healthy corona
 and sparks were starting to jump from the primary to the secondary.  I then
 used some remaining 6 inch pipe to cover the secondary to within 2 inches of
 the top.  This stopped the sparkover. By gap 13 (wide open) I was getting
 some sparking through the 6 inch cover pipe and some small burning on the
 outer edge, but no damage to the secondary.  Putting the torroid on stopped
 most of this, but to get rid of all the primary / secondary arcing I had to
 put extra metal on top of the torroid.  Actually it was rather interesting.
 Tire irons, wheel braces, aluminium spirit level, wood saw, pieces of copper
 pipe.  All provided a different set of spectacular (relatively speaking)
 spark patterns (great photos - I hope).  I hung a grounding wire down from
 the roof frame of the garage to provide a better earth. That was better for
 a single spark, but played merry hell with the radio.
 
 I then, (the caps being well exercised by now) tried one cap.  Very poor by
 comparison.  What is happening?  In theory I need 0.0127 uf for my power
 supply and here I am getting good performance (or am I?) off of 0.005 or so.
 Or have I done the sums wrong again (fool that I am).
 
 Sorry to put all this your way, but I am really pleased with myself today.
 I have made a quantum leap (in my terms) and I would like to know what is
 happening here.  One thing that is apparent is the popularity of the flat
 coil.  The voltage buildup on the secondary is a major pain and covering all
 that beautiful coil with plastic pipe is not the way to go <g>.  Next step
 is a *flatty* I would guess...  But I will wait on any replies and insights.
 
 Thanks in advance
 
 Ken
  >>
Ken,

If I understand your primary correctly: Helical, 9 turns, 1.25" between turns
(assuming .10" dia wire) - this would be 8.9 microheneries.

On the caps, I have found that using a K = 2 (instead of 2.3 as the book
says) yields a more accurate number, probably because this compensates for
the fact that the plate separation is always something more than the
thickness of the dielectric due to the fact that it is hard to roll it
perfectly tight and the plates are not perfectly flat.  Anyway, using K = 2,
 I calculate .009 mfd if the dielectric is .125" thick and .012 mfd if the
dielectric is .093" thick.  You did not say exactly how thick it is.

Your secondary should be about 7.8 mh with dia. = 2.25", winding length = 26"
and 51 turns per inch.  The self resonant frequency of this coil should be
876 khz unloaded and about 594 khz with the toroid installed.  This allows 5
pf effective capacitance for the toroid.

Taped at 9 turns, with the toroid, I calculate a .008 mfd capacitor is
needed.  I get .0037 mfd needed with no toroid installed.

"""So question time please :"""
 
 1.      Why does the torroid reduce primary / secondary arcing

The toroid should reduce the corona around the top of the coil.  It should
prevent sparks from breaking out from the top few turns of the coil.  If it
reduces pri/sec arcing, I am guessing it is because it is changes the tune -
it certainly lowers the secondary frequency.
 
 2.      Why does more metal on top of the torroid get rid of it altogether

Again, adding more metal adds more capacitance and lowers the secondary
frequency. 
 
 3.      Why are my cap calculations all to hell (biggie )

I am not too sure they are.  Mine come out close to yours.
 
 4.      Why do more spark gaps inprove performance (I really feel I should
 be able to answer this myself - but for the life of me I cannot.  I know it
 happens, but not the why)

More gaps = wider total gap = higher voltage.  The wide the gap, the higher
the voltage the cap charges up to before the gaps fire.  Be careful, if you
go to far, it may destroy your neon sign transformers.  13 gaps of .028 is a
total of .36".  In my opinion, this is a lot for this system.  I would be
careful.  I use a total gap of about .150" on my small coil.
 
 5.      Is my coil in tune - it certainly feels like it is - but then I am
 easily pleased. (after a year of failure and balls ups and salt water /
 glass caps I would have been pleased with the spark from an ignition coil
<g>)""""

I think you have done quite well and should be proud at this point.  It takes
a while to get all this working to it's optimum.  I think the biggest problem
that you have right now is because of the helical primary.  It is too close
to the secondary and besides causing direct discharges between the two, the
coupling is probably way too tight.  This will screw up everything, making it
difficult to tune and causing splitting (sparks racing up and down the
secondary).  If you are up for it, I would suggest building a flat primary
using #10 solid copper wire or better yet 1/4" soft copper tubing.  Allow
about 1.0" clearance from the secondary (I.D. = 4.25" or a little larger) and
wind 12 to 14 turns.  15 wouldn't hurt.  A large diameter primary performs
better and provides lots of room for tuning (changing caps and toroids).

Keep at it.

Ed Sonderman






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