[Prev][Next][Index][Thread]

Re: Just a brush



-- BEGIN included message





Tesla List wrote:
> 
> Taylor, Chris CC wrote:
> >
> > I have just recently completed building my first coil and fired it up
> > last night. To my utter disappointment all I got was a big racket from
> > the spark gap and little else.
> >
> > I have a 15/30 neon with a six element spark gap and a plate poly
> > capacitor, (20 plates 10x8" with an 80 mil poly dielectric, theoretical
> > C=0.0085 uF). I haven't got around to placing the cap in an oil bath yet
> > and it doesn't arc unless the gap separation is very large, the cap then
> > arcs around the edges and I shut down and reduce the gap separation.
> > Would the cap be providing 0.0085 uF without the oil bath, I can't see
> > why not, it is my understanding that the oil is only used to provide a
> > better insulator than air around the cap.
> >
> > The coil also has a 1/4" copper tubing primary with 15 turns spaced at
> > 1/4" in a saucer configuration, (30 degree). The secondary is 22 ga
> > transformer wire on a 2.8" PVC pipe with 840 turns, (22.5" long).
> >
> > All I seem to be able to get from this baby is a small brush discharge
> > from the tip of the secondary wire, (primary optimally tapped at turn
> > 5). I have also built an 11 x 3.5" toroid which when attached does not
> > produce any discharge.
> >
> > My questions to the lads are;
> >
> > What sort of diagnostics can I perform to point me in the right
> > direction for larger discharges.
> >
> > Have I missed anything, I have used a number of the circulating formulas
> > to roughly size various components.
> >
> > The coil is working but just doesn't seem the be very efficient. The
> > lowest turn on the secondary is in line with the inner turn of the
> > primary, do I need to lower the primary to get better coupling.
> >
> > Is my secondary too long for efficient coupling, (H/W ~ 8.5) I have read
> > this may be a bit large.
> >
> > The addition of the torus increases the resonant frequency, do I
> > increase or decrease my tank capacitance as the secondary frequency
> > increases and how do I adjust the primary tap as the secondary resonant
> > frequency increases.
> >
> > Any help would be greatly appreciated and will speed me on my way to
> > coilers nirvana.
> >
> > Chris Taylor
> > Perth, AUSTRALIA

Chris,

Your secondary coil is a little long versus its diameter, but you should
be able to get more than just a little 1/2" brush discharge. You didn't
say where your primary tap was located. The symptoms you describe are
usually an indication that the coil is out of tune - instead of the
primary energy going into streamers, its being dissipated in the gap.
Also, the tank cap is a little on the large side for the current rating
of your neon even at 50 Hz, but if the gaps are firing nicely you should
be OK. Also, you're running significant risk of damage to your LDPE cap
by running it in open air. The corona is surprisingly hot, and WILL
surface track and melt paths and holes in your dielectric. 80 Mils of
dielectric thickness is already somewhat low for operation off 15 KV -
you need to put that puppy in oil so before you need to rebuild it.

The secondary/toroid combination should resonate at around 550 kHz. With
the size tank cap and assuming an inner primary diameter of around 4",
you'll have to tap the primary somewhere around turn 7 or 8 in order to
be better in tune. If you're using ALL 15 turns of the primary, it's
oscillating at about half this frequency. I'd suggest leaving the toroid
on, and putting a small screw or tack on the top of the torus to cause
breakout. The size of your torus is about right for this size coil.
Close down your gaps a bit, and begin trying various tap positions until
you get the coil at the point of best tune. I assume you have the base
of the secondary tied to a good RF ground? Also, you didn't say what
kind of gap you're using - a poorly quenching one will limit
performance, but you should still be getting better than 1/2" discharge.
Also, is the wiring between your cap, gaps, and primary short and heavy
gauge (#6 AWG or larger)?

Longer term, I'd suggest winding a new secondary out of at least 4"
diameter PVC, and taking some of the innermost turrns out of the primary
to provide the clearance if necessary. This will allow you to use more
of your primary winding, and should also increase the coupling
coefficient a bit.  A larger diameter coil will run better. Hope this
helps!

Safe coilin' to you!

-- Bert H. --






-- END included message