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Re: [TCML] RF Ground and Brass

Hi Gary,

I've measured (although along time ago), but Terry has also measured several amps (about 10A on one known test coil). I'm not sure why your thinking 350mA (maybe just a misinterpretation).

Here's a document Terry put together. Go down to the area titled "Top Terminal Voltage and Secondary Base Current". You'll see the waveforms.

As of recent, I've been looking to predict secondary base current as it is directly related to output potential (something I'm looking to add in Javatc). I am currently equating base current (without losses) as: Ibase(rms) = (Transformer rms output voltage x sqrt(Sec_Les/Pri_Ldc))/Sec_Reactance I've also checked the above equation against Ibase(rms) = 0.707 * (sqrt( 2 * E_bang / Lee)) and it seems to follow well. I'm just playing with these numbers as this point.

My reason is to pull in the current and voltage profiles along the length of the coil and have the program perform the length conversion for the user. Fantc does this now, but uses a 1A default. The user if desired could take that data and convert to the actual length segments, measure base current, and scale both current and voltage accordingly (that was the idea behind the profile graphs). I'm trying to get Javatc to do all this automatically (for a prediction). I have it running fine on a test program, but I need to make many base current measurements to verify prediction to measurement before I even think about including it. But, my output voltages are much closer to reality which is a "feel good" for me. Even if most are not interested in this type of data about their coil, the base current itself could come in handy simply in wire size requirements.

Take care,

Lau, Gary wrote:
Hi Bart,

I'm curious how you came to noting several Amps of secondary base current.  On what size/power coil?  Are you talking about peak or RMS Amps?  On my 15/60-powered coil, I once placed a small flashlight bulb in line with the secondary base, and I think it only registered a modest glow (though my recollection is also dim).   I recall that Terry Fritz (in a post dated 7-21-2000) had measured his base current, also with a 15/60 NST, as 350mA RMS.

Regards, Gary Lau

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of bartb
Sent: Tuesday, March 04, 2008 10:03 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] RF Ground and Brass

Hi Gary,

There can be several amps on the secondary base current to ground (much
higher than the currents in the secondary which diminish over length)
and in some coils too high for 18 awg if it was a continuous current.
However, this current is time dependent, so I agree that smaller wire
size can be used.

I run 18 awg hv wire from the base to a terminal point (about 12"
length). From the terminal point to RF ground I use 6 awg high strand,
about 1 meter length. I haven't noticed the 18 awg getting warm, so I'm
sure the small length from base to terminal is fine. Like everything
else, if after running, a coiler finds the base current wire warm, then
it's time to go bigger (thermal losses are never good). But if it's at
ambient temp then "all is good".

BTW Gary, I received my fiber optic cable and voltage converters today.
So hopefully I can get this bps measurement going soon. Just need to
proto up a simple circuit and I should be off and running (hoping for
this weekend).

Take care,

Lau, Gary wrote:
Hi Scott,

I think folks often go overboard with unnecessarily large RF ground cables and
connections.  It's important to remember that the actual RMS current in these
conductors is very small.  It may be useful to use a fat conductor for portions that
are very long, as a means of minimizing conductor inductance, but I'm not even
sure that this is critically important.  Minimizing the total conductor length to the
ground rod(s) is probably the most useful point.  But for a couple feet or less from
the secondary base to a central tie-point, it's pointless to use anything heavier than
simple stranded #14 or #18AWG - it only needs to be heavy enough to not be
fragile.  Same with the connection to the NST, Terry filter, and strike rail.  I don't
think copper vs. brass makes any difference for the ground connection, but since
wire is typically copper, I would use that.
The secondary base connection method advocated in the COILBUILD documents
is silly.  These are very old documents and in need of revision.  Trying to secure a
copper strap ground conductor to a copper plate, both subject to surface oxidation,
with a rubber band, sounds like a very poor and unreliable connection.   I use a 1/4-
20 screw connection to each end of the secondary, as both a mechanical and
electrical connection.  See http://www.laushaus.com/tesla/secondary.htm  If you
don't have access to press-fit threaded inserts, there are other ways using common
Your EMI filter hookup sounds correct.  My thoughts on the topic are at
As for surge protectors in a power strip, I've always wondered whether they are
attempting to protect against differential (hot to neutral) spikes, or common mode
(ground to hot & neutral) spikes.  IMO, common-mode spikes are more likely, so
I've added a couple of MOV's inside of my Variac case from hot & neutral to
Regards, Gary Lau

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Scott
Sent: Sunday, March 02, 2008 7:49 PM
To: tesla@xxxxxxxxxx
Subject: [TCML] RF Ground and Brass

Hi all,

I hate to touch on two topics that are so widely discussed here, but I have
a question that kind of falls into a gray area.

First off, I'm on the last stage of my coils construction, the
grounding. This topic has been fought over many times on the list (I just
spent 2.5 hours reading over all the entries about RF ground) and have
decided on the following scheme:

Connections to RF ground:
--Secondary Coil, follwing these insuctions :
--NST case
--Strike Rail
--"RF Power Ground" line coming out of Terry Filter.  (The "NST Ground" line
coming out of the Terry Filter will go into the NST case I guess...refer to
the Terry Filter diagram to see the lines I'm refering too ;) )

Now the Mains supply will go like this:
1.) A power strip with a surge protector will plug into a wall outlet
2.) From the surge protector, a cable will go into a EMI Filter, from Tesla

The side with the 3 terminals will be hooked up to the output from the surge
protector, with the center terminal being the ground.
3.) The side of the EMI filter with 2 terminals will run into the NST's hot
and neutral inputs.

Simple Enough right?

Now the RF ground itself will be right next to the coil: outside, 4 steel
spikes hammered 3 feet into the Earth.

Now here's my question:
I have this ribbon coming off the secondary coil and 10 AWG wire coming from
the NST case and strike rail, how do I actually connect them all together to
the physical RF spikes?  I was just gonna solder the ribbon to the spikes,
and then thread the other wires through a hole in them.

And a second question:
For the metal grounding ribbon coming off the secondary, does it need to
copper for sure?  I wanted to use brass instead.  At my hardware store,
brass is 1/4 the cost of copper and available in more thickness's.  And does
the ribbon need to go all the way from the secondary base to ground
spike?  It would be 3 feet of ribbon that way even is the coil is right next
to the RF ground!

Also, the grounding on the Terry Filter seemed a little weird too, maybe
someone could confirm could I'm doing it right as described.

Sorry for the massive post again, but I have been piecing together this
problem for the better part of the day, and would like some loose ends tided

Thanks for all responses!

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