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Re: Impedance

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

Original poster: d a <btoc3000@xxxxxxxxxxxx>

I read this from: <http://users.tkk.fi/~jwagner/tesla/tc-plans.htm>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 have 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? Significantly 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