RE: [TCML] primary tubing

["Lau, Gary" <Gary.Lau@xxxxxx>]

If we agree that things would be a wash if the aluminum conductor diameter was increased to normalize the DC-resistance, then I don't see any suggestion that aluminum is inferior at RF frequencies any more-so than at DC.  It's your statement suggesting that the resistance if frequency dependant that I take issue with.

Perhaps we're in violent agreement that it's simply better to just use copper for the primary conductor, which is fine.  I've just seen too many who beleive that ANY use of aluminum in a Tesla coil is unsuitable because skin effect will render it a lossy and terrible conductor, which just isn't true.  I've seen folks suggest that one should not have solid aluminum electrode holders and supports in an RSG, which is just silly.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of DC Cox
> Sent: Saturday, November 07, 2009 3:43 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] primary tubing
> 
> Make some peak current measurements, ie, cap discharges, and you will note a
> difference of several hundred amps in larger coils, something I consider
> significant.
> I made these measurements back in 1973, at the suggestion of one of my
> college Profs, and noted the peak current differences.  As you correctly
> point out, if the size is increased significantly this will wash out, but
> usually with tight primary packing this is not a viable option.
> 
> D.C. Cox
> 
> 
> 
> 
> On Fri, Nov 6, 2009 at 8:36 PM, Lau, Gary <Gary.Lau@xxxxxx> wrote:
> 
> > DC,
> >
> > I have refuted this oft-repeated but mistaken belief of yours that aluminum
> > exhibits some frequency-dependant resistance, several times in the past and
> > I will continue to do so.  It does not, to any significant degree.  I have
> > made frequency-sweep measurements of the AC resistance for many different
> > conductor geometries, including Al vs. Cu.  Of course the aluminum has a
> > higher resistance than copper, but this is due to the intrinsic resistively
> > difference between them and is NOT frequency dependant for the frequencies
> > that we are interested in.  If the aluminum conductor diameter is scaled up
> > to compensate for the higher resistively, it's a wash.
> >
> > There are many good reasons to choose copper conductors over aluminum and I
> > wouldn't use anything but copper myself, but frequency-dependant resistance
> > is not one of them.  Please either supply quantitative evidence of your
> > claim, or stop propagating this myth.
> >
> > To Neal's question - Primary resistance is a very bad thing for Tesla
> > coils.  Every (reasonable) effort should be made to minimize tank circuit
> > resistance, if you're going for maximum performance (and not everyone is).
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > > -----Original Message-----
> > > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > > Behalf Of DC Cox
> > > Sent: Friday, November 06, 2009 5:54 PM
> > > To: Tesla Coil Mailing List
> > > Subject: Re: [TCML] primary tubing
> > >
> > > At RF frequencies aluminum is a poor conductor as compared to copper.
> >  Use
> > > copper for HF applications.  Alum will limit your peak RF current,
> > something
> > > you don't want to do.  Peak RF current determines peak magnetic field
> > which
> > > of course links all your power into the sec inductor.
> > >
> > > Dr. Resonance
> > >
> > >
> > >
> > >
> > > On Fri, Nov 6, 2009 at 5:25 AM, Neal Namowicz <neal@xxxxxxxxxxxxxxxx>
> > > wrote:
> > >
> > > > Hi guys,
> > > >
> > > > A quick question re: materials for primaries. I realize that copper
> > tubing
> > > > is kind of the standard for winding primaries. However, while checking
> > out
> > > > the boilers at work it occured to me that a lot of aluminum tubing is
> > used
> > > > for gas valve vent lines, etc., and I was wondering if anyone has ever
> > tried
> > > > it on a primary. From a cost standpoint it's much cheaper, so is there
> > any
> > > > reason to not use it for a primary?
> > > >
> > > > On another note, I liked that sign, too! I should've had that up on my
> > > > front porch on Halloween. I sat out there with my coil, trying to scare
> > the
> > > > little buggers as they came up for candy. Gotta say, for most of them,
> > their
> > > > desire for sugar overcame any qualms about getting closer (still well
> > out of
> > > > reach, though) to the coil. Come spring, I hope my wife doesn't mind
> > the
> > > > grounding rod sticking up from the middle of her flower bed. Ah, she'll
> > get
> > > > over it!
> > > >
> > > > Thanks for your thoughts on the tubing,
> > > >
> > > > Neal.

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