Re: Electrical Properties of Brass

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

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 ?