Re: Thoughts on Tesla coil grounds...

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I'd have to agree with Antonio... This seems really high.. A single wire,
not in a loop, just hanging out in space, is around 1uH/meter. Of course,
what we are really worried about is circuit from top load to ground.  To a
certain extent, you WANT high inductance and low DC resistance on the green
wire ground.  This means that that the RF voltage lifts only the chassis of
your TC stuff, and not everything else in the house, but that for safety
reasons, the TC chassis is grounded at 60 Hz.

To take a horrible example, say you connected the bottom of your TC
secondary to the green wire ground in the power cord, which stretched 20
feet across a garage floor, then to the outlet, then to the service panel,
then to the UFER or water pipe service ground.  The TC topload is
essentially a capacitor with reference to the ground surface under the
coil.  The entire circuit would then be the C topload, the secondary L, the
inductance and resistance of the power cord and wiring back to the panel
and then back to under the coil.  There would be significant capacitive
coupling from the green wire to the ground under the cord, too...

On the other hand, the chicken wire ground plane approach (which is what I
use) connects the bottom of the 4"x20" secondary coil to a 4x4 foot chunk
of chicken wire laying on the floor.  Not only is most of the RF voltage
developed between the chicken wire and the toroid, but the capacitance from
the chicken wire to the ground is probably fairly high (I'll have to try
measuring it), and the sheet inductance of the chicken wire is probably
fairly low.  I DO have the chicken wire connected to the safety (green
wire) ground as well, but, by a fairly small gauge wire.  I have never
noticed any RF voltage on the chassis components, etc., although I haven't
measured it to be sure.  This particular coil is a peculiarly good RF
radiator too...(The curse of being an RF engineer, things that you don't
want to radiate (i.e. TCs) do, and things that you do want to radiate (i.e.
antennas) don't)

Tesla list wrote:
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Antonio,
> 
> At 07:06 PM 7/16/2001 -0300, you wrote:
> >Tesla list wrote:
> >>
> >> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >
> >> I then measured the inductance of the AC wire (A long (25 foot heavy-duty
> >> extension cord).  I have jumpered this outlet's ground to the water pipe
> >> independent of this outlet's normal AC ground too.
> >>
> >>         AC line ground (eventually ties back to water pipe): 426uH
> >>         Resistance:  0.247 ohms
> >
> >The inductance seems quite large for straight wires. How did you measure
> >it? (I made some inductors in this range, and they take a lot of wire
> >in a pot core...).
> >
> >Antonio Carlos M. de Queiroz
> >
> >
> 
> I just used a 1000Hz hand held LCR meter.  I am not sure how much wire is
> in the whole ground loop.  There is some AC noise that made the meter jump
> a little too.  Outside of the loop, the ground and neutral wires go all
> over the house and the nearby neighborhood too.  All things considered,
> Probably not a good RF ground :-))  The direct cable to the water pipe
> seems far better by a few orders of magnitude in many ways.  I am a bit
> surprised at how bad the AC line ground is considering I did try to make it
> a little better than a typical AC outlet ground...
> 
> Cheers,
> 
>         Terry