Re: Electrical Properties of Brass

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi,

"I" would never use aluminum.  Aluminum forms thick (skin depth thick) 
resistive oxide layers.  These are terrible for RF currents.

The resistivity for pure Al is 2.7e-8 so at first it looks like a good 
choice.  But a 10 mil layer of fluffy white AlO2 and it goes bad 
fast...  Since pure aluminum oxidizes in minutes and can reach 5 mil in a 
day easily, the RF resistivity can be just about anything but is generally 
bad.  Other metals form oxide layers too but they are far thinner than 
those of aluminum.

Many people do use aluminum, but I would avoid it.

Cheers,

         Terry

At 05:03 AM 4/19/2003 -0700, you wrote:
>Terry,
>
>That's really interesting! Can you do a similar
>analysis of aluminum roof flashing? I've often thought
>about cutting it into 1" ribbon and using it for
>primary coil stock.
>
>Regards,
>
>--- 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 ?
> >
> >
>
>
>=====
>Gregory R. Hunter
>
>http://hot-streamer-dot-com/greg
>
>__________________________________________________
>Do you Yahoo!?
>The New Yahoo! Search - Faster. Easier. Bingo
>http://search.yahoo-dot-com