Re: Electrical Properties of Brass

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

Original poster: "Jeremy Scott by way of Terry Fritz <teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>


Thanks Terry,

I think I am going to use copper strips instead.
I'm more worried about loss of power in the tank
circuit than I am about the eventual oxidation
of the circuit. (You can always sand copper, but
you can't easilly modify the electrical properites
of brass... :) )

I'm glad Finn replied to this thread, I am
designing a primary similar to his that allows
the tap to be adjusted as the coil is running.
I was worried that after time, the copper would
oxidize and make the sliding tap less effective.
I could probably attach a small bit of sandpaper
to the side of the tap so it clears oxidation
as it moves :)

I've already designed the thing in AutoCad and
pspice, so others can build it as well.

I'm just now beginning to fabricate the parts. The
rotating primary tap support has been partially
manufactured. The whole thing is made of red oak,
which will look really nice when finished with a few
layers of PU varnish.
(Primary supports are HDPE)

Another thing, I was browsing through the archives
on hot-streamer and I came across your "ground box"
which basically provides ground points for the
secondary coil and saftey grounds for lower voltage
parts. The box is then connected to a pipe ground
via RG-8U cable, at which point the sheild and center
conductor are connected to each other.
I was wondering, what is the maximum length of the
cable, what sorts of things are acceptable to connect
to the saftey ground, and finally what level of power
is this thing effective to?
I haven't yet designed a ground connection into my
system, other than 1" dia copper pipe that extends
down from the bottom of the coil to the ground. (If I
had a
6' ground rod in the middle of the lawn I could
theoretically plop the whole mess on top of it :)












--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Jeremy,
 >
 > Resistance = Resistivity X Length / Area
 >
 > The numbers I have here are all in meters.
 >
 > Copper = 1.7 x 10E-8  Ohm-Meters
 > Brass = 6.39E-8 Ohm-Meter
 >
 >
http://www.matweb-dot-com/search/SpecificMaterial.asp?bassnum=MBRASE
 >
 > So brass is about 4X more resistive than copper at
 > DC.
 >
 > Skin Depth = 1 / SQRT(pi x f x Resistivity x
 > Permeability)
 >
 > Permeability = pi x 4e-7  H/m  X  Ur
 >
 > Ur copper = 1
 > Ur brass = 1.05
 >
 >
http://www.npl.co.uk/electromagnetic/dclf/magnetics/lowpermeabilitylc.html
 >
 > So the skin depth is about 1/2 that of copper since
 > the resistivity is 4X.
 >
 > The skin depth of copper is 2.602 / SQRT(F) inches.
 > At 154kHz that is
 > 0.00663 inches.  So brass is roughly 0.0033 inches.
 > Your 16mil brass is
 > perfect.  At 2 inches wide, it is about the
 > equivalent of 0.159 inch copper
 > tubing.
 >
 > So I will say your brass strips will be about 50%
 > more lossy than 1/4 inch
 > copper tubing.  Lots of "if, ands, ors, and buts"
 > too all this... but the
 > brass will work "ok" for a 15/120 NST system.  You
 > may loose about 2 to 4
 > inches as compared to 1/2 inch copper tubing or
 > something but probably not
 > a big deal.
 >
 > Cheers,
 >
 >          Terry
 >
 >
 >
 > At 04:28 PM 4/18/2003 -0700, you wrote:
 > >Hi!
 > >
 > >I was wondering if anyone has any experience with
 > >building primaries out of brass instead of copper?
 > >I want to use brass since I'm worried about copper
 > >oxidizing over time.
 > >
 > >I have a design in mind that is going to use
 > >brass strips for all connections in the tank
 > >circuit. (Including the primary)
 > >
 > >The brass strips I have in mind are approximately
 > >.016" thick by 2" wide.
 > >
 > > >From calculations I have done with JavaTC,
 > >the tank current at gap conduction is going
 > >to be approximately 800 Amps.
 > >
 > >(15KV/120mA NST .03 uf LTR primary cap)
 > >(154kHz resonant frequency)
 > >
 > >I am concerned that the brass strips I've got
 > >are too thin to handle this current load.
 > >Unfortunately, anything thicker is tough to work
 > >with and bend into the proper shapes I require.
 > >(Doubling up the thin strips is an option but
 > >I don't want to do it if i don't have to.)
 > >
 > >On the otherhand, since the tank current will be
 > >oscillating at RF frequencies, skin-effect tells me
 > >that the thickness isn't as much of an issue as the
 > >actual surface area.
 > >
 > >I guess the real question is, how far does a charge
 > >of 800A penetrate into brass at 154kHz ?
 >
 >


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