Re: Electrical Properties of Brass

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

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 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 ?
> >
> >