Re: Coil just won't fire...

Subject:  Re: Coil just won't fire...
  Date:   Wed, 16 Apr 1997 17:18:20 -0500
  From:   "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>

> >       Mike...my partner and I have met with a problem. We have built a coil
> >(description to follow) that just won't fire.We can tease a few 6 inch
> >arcs from it using a grounded rod, but it will not fire in free
> >air. Before I go on, I'll decribe this tiresome albatross to you.
> >       
> >       Secondary
> >       The total winding lenth of this 3 1/2" coil using #26 copper wire is 17
> >1/4 ".The length of the PVC pipe is about 22 3/4" long,leaving about 2
> >1/2" at the top as a header and 3 1/8" at the bottom (the top and bottom
> >numbers represent pipe with no windings).
> >The ends of the pipe are sealed with plexiglass and the top has a 1/4-20
> >X 1/2" bolt sticking out the top as a means to secure a torid.The copper
> >wire from the winding is terminated at this bolt.
> >       
> >       Capacitors
> >The capacitors we are using are 6 long necked beer bottles filled with
> >sea salt and motor oil.The total capacitance of these bottles is about
> >.0043 uF.We did have one of these capacitors fail while trying  our
> >first coil (too large a spark gap) but these seem to be alright now.
> >       
> >       Primary
> >Our primary coil is made from .375" copper tube wound in conical form
> >with.375" spacing.The form and spacing is maintained with a wooden and
> >plexiglass form.In total there are just over 15 turns on this coil
> >       
> >       Transformer
> >Our transformer is a 9KV 120 mA neon .
> >       
> >       Spark Gap.
> >The spark gap is made from 2 pieces of 3 1/2" X 3" X 1/16" copper plate
> >set up over a quenching fan and set at between .020" - .030".
> >
> >       Torid
> >We have 2 torids that we tried.One was  20"X4" made from Aluminum dryer
> >duct held together with pizza pie plates and Aluminum tape.The other was
> >about 8"X 2 1/2" styrofoam covered in aluminum tape.
> >
> >We have built a control pack that engages/disengages the capacitors and
> >bleeding resistors. This control also houses the autotransformer that we
> >use to control the primary voltage to our neon transformer.
> >When we attempt to fire this coil there appears to be nothing
> >wrong. There are no stray arcs,there is no overheating anywhere in the
> >ciruit. When we turn up the autotransformer to produce 180 Volts at the
> >neon primary we are drawing around 20 + amps (we did trip a breaker
> >while setting our spark gap ). We have plenty of arcing at the spark gaps
> >(the safety gap does not fire) We allowed this coil to try for about 10
> >minutes in total without any physical failure (ie we could still draw 6
> >inch sparks from the torid when we finally gave up). We even tried to use
> >an old secondary that we have laying around...It did not do any 
> >better. We were able to get the 6" arcs by tuning the primary out to it's
> >maximum setting of 15 + turns. We were drawing 20 + amps and the power
> >was not  being consumed by over heating and/or sparks, so we were
> >wondering, could this be a coupling problem? If anyone has a suggestion
> >or idea we would very much appreciate the help. 
> >
> >                                       Two VERY distraught coilers
> >
The thing that most comes to mind on first read is that your spark 
gap is lacking, shud be a multi-gap design (6+ separate gaps) and 
your neon being a 120 mA job is capable of quite a lot of current and 
is not loaded in the least by your very small capacitor size.  I 
think the gap is probably power arcing, killing the RF oscillations.  
For this system build a decent gap system and try that first.  If 
that doesn't do the trick the effort wont be wasted.  Then get a 30 
mA neon transformer and try that.

Good luck,