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RE: Geek Group Cap mod

Original poster: "Dave Larkin by way of Terry Fritz <twftesla-at-qwest-dot-net>" <teslaman15-at-hotmail-dot-com>

Me and my big mouth..... ;-)

Well, my reasoning for the 40kV rating was thus - The puncture rating of 
glass is 250V/mil by the book.  The bottles I've smashed and measured all 
had walls around 3/16th" thick, which equates to ~ 47kV.

However the creapage path seems to be the weak link. On you average longneck 
(assuming salt or brine to the level of the beginning of the neck) there is 
about 3" of creapage path.  The value I found for glass in air is 
12.5kV/inch.  So 37.5kV.  Accounting for a thin skim of oil on the surface 
of the brine I rounded up to 40kV.


>At 01:46 AM 5/6/2002 +0000, you wrote:
> >Comments interspersed.........
> >
> >
> >>Original poster: "Dave Larkin by way of Terry Fritz 
> >><teslaman15-at-hotmail-dot-com>
> >>
> >>
> >> >Hi Bert,all,
> >> >I donít expect to get 80KV, heck I only have two 9KV NST's. I was just
> >> >going by what the site said and using their building technique. They
> >> >claim this design will be perfect for a 15/60 and they rate this cap 
> >> >80kv/.0125 mfd.
> >> >Would someone take a look and see if I misunderstood the internal
> >> >wiring?
> >>
> >>No misunderstanding on your part... The geek group are not renowned for
> >>their technical competance,
> >
> >I'm sure the 200+ members, several of whom are on this list, will love 
> >one.
> >
>Nice to know you are still reading the mail :o))  I thought to myself,
>Hmmmmm... I wonder if Chris is awake :o))))  I got a kick out of it ;-))
> >
> >
> >>I suspect the 80kV rating was based on either
> >>severely flawed reasoning.
> >
> >Actually, years ago when we built them we asked what the breakdown 
> >was and were told "Don't worry about it it's something like 80kV" so 
> >what we wrote on the caps. When it came time to do the site, I went and 
> >the caps, and it went on the site. I've never given it much concern.
> >
> >>A more sensible DC rating for a longneck beer
> >>bottle (miller, corona, becks etc.) would be 40kV or so, depending on 
> >>condition of the glass and the creepage path down the neck.
> >
> >Prove it, then I'll change the site, the caps, and the manual.
> >
>I set up a little test tonight to hopefully salvage our reputation a bit 
>I was "thoughtfully" holding a Miller Draft long neck as I read your post.
>It's a tough job, but somebody has to do it!!  I "cleaned" the bottle out
>and made a quick little capacitor out of it:
>I then set up the Bertan lab X-ray power supply to put it to the test:
>There you go.  At the 50kV limit of the supply, the bottle held "just
>fine".  I suspect most of the 67uA of leakage current was from corona of
>the wiring which was "sizzling" with electricity.
>After awhile it started to get a nice blue corona band to the ground foil.
>It was about 5 inches long and 1.5 inches wide and bright blue.  It was
>really cool!!  Then POWWW!!!  The two terminals arced over.  It was
>interesting that it did not track on the bottle but choose an air path
>about 1 inch away from the bottle neck.  It seems very high voltages just
>go where they want and tend to ignor the surface tracking thing.  I did not
>use oil as your bucket cap does to prevent this.  If I had, the arc over in
>air problem would have been eliminated.  I almost wonder if the oil is
>needed for normal TC use?  But I am reminded of things like:
>So a Miller Genuine Draft long neck holds 50kV seemingly without a problem.
>  Remember that beer bottles are very high tech and the process of making
>them is very highly controlled so quality is very high.  Even though the
>glass seems thin, it's the best glass available and it is molded to very
>high standards.
>	Terry
>	G3 #1043

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