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Re: [TCML] Single-ended NST, wiring
On 3/5/13 5:42 AM, jhowson4@xxxxxxxxxxx wrote:
alright so apparently i missed something all these years.
I thought you wanted to separate the two grounds and because the HV
was grounded you should only use the RF ground in that system, but
apparently not, you use both.
You want to connect the ground on your transformer to the house
ground, make your circuit like you have shone, and connect the
bottom/inner turn of your primary to the base of your secondary.
No.. there is no good reason to connect primary to secondary. Some
people do it for historical reasons, but for the vast majority of cases
this isn't a good idea.
If you are using a Neon Sign transformer, or anything with a grounded
centertap, connecting primary and secondary as you describe is
DANGEROUS. On a typical NST driven primary, both ends of the primary
are "hot" relative to ground.
This is what DC Cox (Dr. Resonance ) did with his permanent coil
installations (DC cox was a Tesla coil powerhouse, owning his own
company and such that built them)
" We always ground one of the HV bushings (either H1 or H2) to the
main 220 volt ground.
This is for a pole transformer (pig), and he's grounding one of the HV
terminals. That's a good idea in this case, because it limits the
maximum voltage on the other terminal.
This then goes from the power supply over to
the coil via standard 10 AWG THHN wire and when connecting to the
spark gap, it also connects to the inside of the pri Tesla
transformer copper tubing and also to the main RF ground.
Making the inside of the primary low potential (near ground), so the
voltage between bottom of secondary (also near ground) is lowest.
bear in mind, though that a wire to a "earth ground" has significant
impedance at 100kHz. (figure 1 microhenry/meter, and at 100kHz, that's
about 0.6 ohm/meter. )
The base of
Tesla coil sec also connects to the main RF ground. We then run a 2
ought fine stranded welding cable to our main bldg ref ground which
is connected to 2 parallel external copper grounds outside. In our
museum applications we always have them install a 2 ought welding
cable from dual exterior bldg ground directly to the demo stage area
where it terminates as the base of the Tesla sec coil, ie, main RF
ground. Dr. Resonance "
I would question the value of that 2/0 cable. The AC resistance and AC
impedance isn't all that much different between 2/0 and, say, AWG 10, at
least as far as a TC goes.
To a certain extent, things like this go that way because "we did it
that way in the past and it worked, why change" not on the basis of any
analysis or test. In a professional installation, the cost of the wire
is small compared to the labor to install it. And, over the years, most
TC exhibitors with big coils scrounge up a roll of big ground cable
(hoping for low copper prices!) and just use it over and over.
Thanks, John "Jay" Howson IV
"Why thank you, I will be happy to take those electrons off your
hands."
----- Original Message ----- From: "Jacob Karlström"
<94jac12@xxxxxxxxx> To: tesla@xxxxxxxxxx Sent: Saturday, March 2,
2013 3:07:51 PM Subject: [TCML] Single-ended NST, wiring
Hello,
The NST (4kV, 50mA) for my SGTC is a single end type with one of its
secondary winding ends attached to the metal casing. I have seen
schematics of other TCs with single-ended transformers, and they have
all looked like this:
http://www.physics.gla.ac.uk/~kskeldon/PubSci/images/tesla3.gif with
the capacitor in parallel with the transformer and coil. However, I
recall reading that a capacitor in parallel is not preferred in a TC
using an NST. I am wondering if connecting the capacitor in series
instead like this, http://imgur.com/JegqUiI, would work, or will
there be any problems with the capacitor + ground?
Regards,
Jacob Karlström _______________________________________________ Tesla
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