Re: Impedance

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: d a <btoc3000@xxxxxxxxxxxx>

Thanks for the explaination!

Just one last doubt...
"Am I right to say that RF current and voltage is different
from the HV current and voltage that we are getting at the secondary topload?"

What I meant is that is "RF current and voltage" the same type/class 
as "High voltage and current"? We always hope to have a large output 
at the topload, so why are we trying to drain off this source of RF 
current and voltage?

My hypothesis is that this class of RF current and voltage is 
different from the HV we are getting at the topload and this RF is 
actually harmful and dangerous thats why we wish to ground it off?

Regards
Sam
Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: "Antonio Carlos M. de Queiroz"

Tesla list wrote:

>Original poster: d a
>
>I read this from:
>http://users.tkk.fi/~jwagner/tesla/tc-plans.htm
>and I have some queries...
>The Tesla coil secondary RF ground must be an own ground separate
>from mains ground. Reasons:
>1) this separate ground will sink RF current and voltage, which - if
>you used mains ground - would fry all equipment in your house, even
>the surge protectors.

Very probably.

>2) also, the mains ground wire is way too thin, and would have a
>considerable impedance at the high frequencies present. High
>impedance is not nice, as the TC base wouldn't be properly grounded
>then, and the wire would ha ve a voltage drop from some 10s of kV on
>the base to 0V somewhere along the wire - i.e. the thin wire could
>still have a few kV some meters away from the coil base (corona,
>electrocution, damaged equipment etc).

True, but not because the wire is thin. The currents are quite low. The
problem is the inductance of the wire, that results in significant
reactance at TC frequencies.

>3) the other thing that is bad about a high impedance ground is that
>the zero voltage node will shift down along the wire to the place
>where the solid ground is. This will cause a phase shift also in the
>TC secondary, meaning you could get breakouts from any part along
>the coil, not just the top.

Wrong. This can't happen.

>for 1) Am I right to say that RF current and voltage is different
>from the HV current and voltage that we are getting at the secondary topload?

At the ground connection? Signifi cantly higher current and much lower
voltage (but that can still be in the kV range).

>for 2) Why would thin wire have a considerable impedance at the high
>frequencies? Is there a formula for this?

Wire inductance. About 1 or 2 uH per meter, depending on length, thickness,
and surrounding magnetic materials.

>for 3) In layman terms, does it mean that having a poor ground will
>cause the zero voltage node to "shift" to the solid ground. What is
>the "solid ground" here?

Doesn't happen. Extra wire in series with the bottom of the secondary coil
is just some extra inductance and a bit of resistance (insignificant in
relation to the resistance of the secondary coil).

Antonio Carlos M. de Queiroz