Re: not conducting secondary to ground.

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Date: 19 December 2000 02:21
Subject: not conducting secondary to ground.


Hi Pholp!


>Original poster: "Pholp Smiff by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<kawanze-at-hotmail-dot-com>
>
>
>
>I want to display my tesla coil indoors

<snip>

> 1.  Electrically connecting the bottom of the secondary directly to the
>primary - so capacitance is between toroid and primary circuit rather than
>ground.


Yeeeeouwch!  No, **please** don't do this.  Potentially lethal if things go
wrong.

>
> 2.  Don't even bother connecting the bottom of the secondary to anything,


Now this sounds like it won't go anywhere, maybe, but I'll tell you a story.

I'd set up my old 500VA coil in the garage on a wooden stand, and as I hadn't
used it for a while was busily checking the connections to the gap, the
caps etc
and, having satisfied myself all was well, fired up and enjoyed the show.  Then
I switched off and went to short the caps and feel how hot the gap was getting
(barely tepid after a minute).  It was then I noticed the earth lead wasn't
connected to anything and the end of the secondary wire was just resting on top
of the wooden stand ;-)

It didn't make any difference!

So if your coil is as inefficient as my old one (unloaded Q = 35 thanks to
carbonised strikes on the polyurethane!) you may well get away with it!  The
earth resistance only seems to matter if the rf resistance of the coil is very
low (i.e. the Q is very high) as it acts in series with the resistance of the
coil.  If the coil isn't too efficient to start with, the earth resistance
doesn't make much difference and the base of the secondary probably gets
all the
earth it needs through stray capacitance.

The funny thing is, the carbonised strikes and low unloaded Q seem to have made
no difference to the sparks  8-[] (eyes bulging & gaping in incredulity)
with or
without an earth connection.  Aren't these things fascinating?

So I'd suggest just leaving the end of the secondary wire wherever it wants to
lie, not connected to anything.  The sparks from the toroid will shoot off into
free space as per usual.  But I would put a stand of some kind under the coil
rather than leave a bare wire in contact with a carpet which might ignite if
sparks from the base wire of the secondary get in it.

Dunckx