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Re: Bottle Caps; First Firing
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Saturday, November 15, 1997 9:33 AM
To: Tesla List
Cc: ghunter-at-mail.enterprise-dot-net
Subject: Re: Bottle Caps; First Firing
>
> From: ghunter-at-mail.enterprise-dot-net[SMTP:ghunter-at-mail.enterprise-dot-net]
> Sent: Friday, November 14, 1997 5:00 PM
> To: Tesla List
> Subject: Bottle Caps; First Firing
>
> Just fired up the little 4.5" x 23" TC for the first time. Tuning
> up was a pain. Took me an hour to find the sweet spot on the primary.
> Sparks were only 6 to 8 inches. A bit disappointing. I can see
> part of the problem right off. My foil-covered wine bottle caps
> (5 caps for .0056uF total) glow with lavender corona. The loss must be
> horrendous. I plan to paint them with melted parafin in an attempt
> to suppress the corona.
>
To increase your capacitance and reduce corona to a minimum,
remove the aluminum foil and instead immerse the bottles in a plastic
container filled with salt water. Immerse a strip of metal in the
salt water to act as an electrode for the electrical connection.
All immersed bottles will be in parallel. (tie the tops together).
If you want to place bottles in series, there are two methods.
Method one involves making up two such containers and tying
all the caps in each container in parallel. Then connect the
the two GROUPS in series.
BTW, since such capacitors are AC rated, you can use the tops
as the main electrodes, and tie the two container bases
together by connecting a heavy wire to the metal electrodes
that are immersed in the solution.
Another method is to not have any electrode in the saltwater bath
at all. Instead, use the inside bottle connections only. Imagine
four bottles all in the same container. If you tied the tops of
two bottles together (call this group A), and then tied the tops
of the other two bottle together (call this group B), then if
you used the tops of group A as one connection and the tops
of group B as the other connection, you would have a capacitance
equal to that of ONE bottle, but at TWICE the voltage rating.
Expand the concept to include any number in parallel in each
group, but always have exactly TWO groups per container.
The water height inside the bottles should match the water
height of the water in the container. Make sure you put a
layer of oil over the water in the container. This will retard
evaporation, and reduce surface corona.
You will be pleased to find that the immersion method will
not only reduce your corona, but it will actually increase
the capacitance, since the water will be in intimate
contact with the glass. The extra water will also help
cool down the bottle caps somewhat. It has also been
my experience that immersed bottle caps do not destruct as
violently as foil covered bottle caps.
> I could see a bright corona halo coming from the top turn of the
> secondary winding. It was blowing right through the thick, sloppy
> coatings of gloss urethane. The top windings of my secondary are
> going to get the hot wax treatment as well.
>
Are you using a toroid? That will eliminate the top
corona problem much more elegantly, and will also increase
your spark size (and QUALITY!!!)
> Another problem. My 5k, 50w series power resistors (one per
> transformer leg) are getting hot as pistols. Obviously, they are
> eating some power. I'm going to replace them with 100 turn chokes
> wound on 1" x 5" cylindrical ferrite forms. This will reduce ohmic
> loss while (hopefully) preventing raw RF from reaching my neon
> secondary.
>
Yes, chokes are the way to go if you want to keep losses minimal.
> In frustration I opened the gaps up wide. The 15kv neon could just
> barely fire them. Sparks increased to about 12" and the noise was
> deafening. The safety gaps were firing like mad. Gave me the
> creeps. I know this treatment is hard on both the neon and my vino
> bottles. I put the gaps back to a sane setting. I'll pursue longer
> sparks through incremental improvements in efficiency instead of
> blowing up my neon & cracking glass. Sure was fun though. I wanna
> build a bigger one.
>
Don't open the gaps too wide or you may lose your caps and/or
your transformer.
What size transformer are you using? Your cap size may be too
small. I had a 4.25" x 24" secondary with a .007 mfd flat cap
driven by two 12KV 30 ma neons. With the proper topload and using
a vacuum gap I was able to get 30" sparks rather consistently,
with the occassional longer streamer. Flat spiral primary, 14 turns,
tapped for best tune between 6 and 7, if I remember correctly.
> Greg
>
>
Hope this helps.
Fr. Tom McGahee