[Prev][Next][Index][Thread]

Re: grounding - this doesn't make sense - wire size

Subject:  Re: grounding - this doesn't make sense - wire size
  Date:  Mon, 5 May 1997 16:28:24 -0400
  From:  "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:  "Tesla List" <tesla-at-pupman-dot-com>
    CC:  <William_B_Noble-at-msn-dot-com>



----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: grounding - this doesn't make sense - wire size
> Date: Sunday, May 04, 1997 12:14 AM
> 
> Subject:  grounding - this doesn't make sense - wire size
>   Date:  Fri, 2 May 97 06:35:58 UT
>   From:  "William Noble" <William_B_Noble-at-msn-dot-com>
>     To:  "Tesla List" <tesla-at-poodle.pupman-dot-com>
> 
> 
> I read about the importance of a high current ground, and the use
of
> heavy 
> wire to connect to it.  Yet the secondary wire isn't all that big. 
I'm
> using 
> 24 gague on a 4 inch secondary - if I remember right the largest
wire
> size on 
> a secondary I've read about on the list is 18 gague???   What I
don't 
> understand is why the wire from the secondary to the ground rod (or
> whatever) 
> needs to be more than one wire size (or 2) larger than the wire
that the 
> secondary is wound with.  IT would seem to me that current is
limited by 
> melting the secondary wire.  Can someone explain.

William,
Your confusion is understandable. 

Think of the thing this way: The secondary of the Tesla coil needs to
be connected to a really really good RF ground for maximum
performance. The reason for this RF ground is so that the secondary
circuit has a good solid SOMETHING to push against real hard and that
(hopefully) won't move. Don't confuse what is going on WITHIN the
coil with what goes on BELOW the coil. In the coil we WANT
inductance. It is the stuff of which resonance is made (not
completely, but indispensible nonetheless). 

The bottom of the coil should ideally be a voltage node (zero value
voltage point), and a current anti-node (maximum value current
point). ANY inductance between the base and the ground is (generally)
going to degrade performance of the coil. It is like trying to jump
up and down. This is easy to accomplish if you jump up and down on
something solid like the ground, but not so successful if you try
jumping up and down on quicksand.

You are right when you look at the dinky size of the wire and say to
yourself "Well, if THAT little wire is able to carry the current in
the coil, then it should be able to carry that same current to
ground."

A really short piece of that wire going in an absolutely straight
line and connected to a good RF ground would indeed be OK. But in the
real world our coils are not always located 2 inches away from our
ground rods!

So, we try to preserve the *effects* of our superb ground rod
assembly as best we can as we actually go through the motions of
connecting it up to the base of the secondary coil. Ideally we would
be using flat, wide copper or aluminum ribbon as short and STRAIGHT
as possible. Flat and wide because that gives us the lowest RF
resistance loss due to the skin effect. Copper or aluminum because
silver is too expensive. (We want the best conductor we can get
without excessively deflating our wallet). SHORT and STRAIGHT because
any twists and turns and the inductance will cause a voltage drop
along the conductor. 

In Tesla coils we always want to keep the
secondary base current as obscenely high as we can. That is why we
focus such keen attention on the RF Ground and the connection to this
RF Ground. Not only must the RF ground be excellent, but the
excellent RF ground does us NO GOOD WHATSOEVER if we do not have an
equally EXCELLENT CONNECTION to this ground. Make that an equally
good RF connection. (We don't want to generate any unneccesary flame
mail here!!)

So you see, it is not a matter of conducting any old current, but a
pretty hefty current that also happens to be operating at Radio
Frequencies. 

Hope the explanation helps.

Fr. Tom McGahee