Re: Puncture voltage

>>From al263636-at-sal.itesm.mx.pupman-dot-comFri Aug 23 22:42:41 1996
>Date: Fri, 23 Aug 1996 09:49:29 -0500 (CDT)
>From: Jorge <al263636-at-sal.itesm.mx.pupman-dot-com>
>To: Tesla-List <tesla-at-pupman-dot-com>
>Subject: Puncture voltage


>	Im fairly new on building Tesla Coils, i recently built a small 
>	one, it uses a 9000, 30ma neon sign transformer. My problem is 
>	with the cap, i live in a small town and theres no where i can 
>	get the poly to build the caps, so instead i used 1/8" window 
>	glass, i sumerged the cap in oil and i also spreaded some in 
>	between the plates, my question is ? Can the cap hold and for 
>	how long ?.
>	Could some one please answer, i know this must be an easy 
>	question for some of you, but im new at this some and im a 
>	little nervous turning on the coil and have the cap blow up. 

>	Thanks

>	Jorge Fuentes						

>*    "World without end,         *
>*     From beginning to the end, * 
>*     We are alive,              *
>*     Forever."                  * 
>*                  "The Celts"   *


When we coilers refer to a glass capacitor 'blowing up' it is just a 
figure of speech.  There is no explosion,... well hardly ever, and most 
of the time the house can  be rebuilt almost as good as new!

I'm just pulling you leg:)  There is no explosion danger with the 
modest energy stored in a typical tabletop system, just the annoyance 
that your cap will have to be rebuilt.  If you have it immersed in a 
transparent plastic container you will see a bit of a light show, 
bluish colour light coming from in between the plates where there may be
trapped tiny air bubbles.  Keep your run times short, 5 to 10 seconds and you
will be probably OK.  Those little blue lights are localized heating 
points working on the surface of the glass.  The failure mode is when 
you see a whitish green light come out the edge of the glass plate as 
the glass itself punctures from localized thermal runaway.  Usually 
this is accomapied by a click noise as the sheet of glass in the pack 
fractures into two or more sections.  The oil bath and sandwhich with 
the other sheets prevents this glass from going anywhere.

An alternate to a glass plate and aluminum foil cap is one made with 
beer or wine bottles.  Fill them with a saturated solutuion of water 
and table, or rock salt to about 2/3rds full.  Place all these 
bottles in a plastic tub which is itself filled with the same brine 
solution so as the level in the outer tub, bucket, etc, is the same 
as the level inside the bottles.  Loop a piece of bare copper wire, 
(#14 works) into all the bottles making good contact with the 
saltwater.  This becomes one terminal of your capacitor.  Run a 
length of the same type bare wire around inside and below the surface 
of the saltwater in the tub.  This is the other connection.  You can 
easily change the capacitance of this capacitor by adding, deleting 
bottles, or by playing with the level in the outer tub.  Once you've 
got the system tuned, you can pour cooking oil over the surface of 
the saltwater, both inside the bottles and in the outer bath, just 
enough to completely cover the surfacwe.  This will keep your water 
from evaporating, thus detuning your capacitor.  
If you use 12 ounce common beer bottles, I think I would start with 
12 bottles, but this is just a guess as I've not built one.  Anyone 
out there know the capacitance of a beer bottle?

Good luck!