Re: School demo

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Hi All.

(snip from Shaun Epp)
> Neet idea, I wanted to do the same soon when I get my almost ready 
> coil finished.  What do we coilers do about the secondary RF ground? 
> an we use a 4 x 4 piece of chicken wire under the coil and connected 
> to RF ground, should we also connect it to building ground via the 
> green wire?
>
> I know the thing I'd do is to stress safty and how dangerous it can be if
> touched or approached and stress to everyone watching that you, to
> operator( and maybe a trusted assistant)  is the only one to operate 
> the switch and approach to coil while operating and after.
>
> All the Best,
> 
> Shaun Epp

For a school demo, I would use nothing other than a "dedicated" RF ground, 
one that is totally separate from everything else.

Using nothing more than a 4' x 4' square of chicken wire for a ground 
(sometimes called a "counterpoise") is going to be dangerous sir. 

How it works, is that it capacitively couples the bottom of the secondary 
coil to ground. (the square of chicken wire is one "plate" of the capacitor, 
the insulator in between is the air, the other "plate" is the earth)

This is not the best at all, but does work. Unfortunately, there is a 
significant voltage at the bottom of the coil. A very significant voltage. 
Set up a coil using a large counterpoise (the bigger the better), and you can 
draw bright hot sparks off of this "ground" with a real grounded wire.

If you were to get close to this (VERY easy to do.......its four foot 
square!) you'd get a very hard zap. You would discharge the capacitance of 
the counterpoise through your body. Use nothing more than a solid 
earth-ground while you're operating for the public. In your workshop (with a 
friend, not by yourself) using a counterpoise is perfectly acceptable.

Of course, if you already have an earth ground, there is absolutely no reason 
to use a counterpoise. 

(btw I have run small coils grounded to the AC ground (building ground) at 
hamfest's before. This has never hurt anything, but it is definately not a 
good idea)

Later,

Justin Hays
KC5PNP
G-3 #1150
Email: pyrotrons-at-aol-dot-com
Website: www.hvguy-dot-com