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Re: Electrical Properties of Brass



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


The brass i was thinking about using
was alloy 260, the kind mcmaster-carr
sells. I looked this stuff up and it's
approximately 70% copper and %30 zinc.

The zinc increases it's rigidity and
helps the copper resist corrosion, but
unfortunately it increases resistance.

I would say that if anyone wants to
make things out of brass, design for
copper and then increase it by 30%
size if you plan on using brass.

P.S. Where do you get that 2" braided
copper strap? My design calls for some.




--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Jeremy,
 >
 > At 10:27 AM 4/21/2003 -0700, you wrote:
 >
 > >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 guess you noticed that were really are unsure
 > about things like this
 > ;-))  Copper is the "safe" choice we all know will
 > work...  Unless you live
 > in a really humid place, oxidation should be a very
 > minor problem.  If a
 > contact wipes the surface, it should stay very
 > clean.  I would look at
 > copper plumbing pipe inside houses in your area to
 > judge how bad corrosion
 > will be.  There are tuner cleaners and such that
 > have oil in them that will
 > really help resist corrosion too.  Automotive
 > switches have grease on the
 > switch contacts but I am not sure what that actually
 > is.
 >
 >
 > >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.
 >
 > Cool!!
 >
 >
 > >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)
 >
 > It sounds really cool!!
 >
 >
 > >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 used it about 1000 watts.  It is about 20 feet
 > long.  I used to know the
 > inductances and all that...
 >
 > >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 :)
 >
 > I would do the ground rod.  Like the copper vs. Al
 > thing, We "know" the
 > ground rod will work were fancy cables do have some
 > questions.  Nowdays, I
 > have 2 inch copper braid going to two ground rods
 > six feet away ;-)
 >
 > Cheers,
 >
 >          Terry
 >
 >
 >
 >
 > >--- 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
=== message truncated ===


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