Re: Electrode holder material for a high-power RSG

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

Original poster: "bob golding by way of Terry Fritz <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>

Hi Mark,
    Just guessing here but I don't think it sounds like a good idea to have
beryllium alloys
anywhere near a spark gap. Beryllium oxides are very toxic. The rotary will
spread it around
liberally I would think.

cheers
bob golding.

Tesla list wrote:

> Original poster: "Mark Broker by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <broker-at-uwplatt.edu>
>
> Hello, all
>
> I am making an RSG that I hope to one day (years away) use with a big TC
> (25kVA) at 3600RPM (thinking 5kRPM *MAX*), though I'll be starting with a
> 1200RPM motor (min speed).  Since I have the resources literally at my
> fingertips until this May, I thought I'd build this puppy now.
>
> An AutoCAD drawing of the whole rotor can be seen at:
> <http://mbroker.tripod-dot-com/TeslaCoil/SRSG.jpg>http://mbroker.tripod-dot-com/Tes
> laCoil/SRSG.jpg
>
> That's a 12" Dx1/2"thick G-10 rotor with 12 electrodes on a 10"D circle.  the
> idea is that the electrode assemblies will be precisely the same lenght (from
> electrode tip to electrode tip) and as symmetric as possible.  They can be
> removed from the rotor by removing the single set screw, and replaced just as
> easily.
>
> A picture of my prototype electrode assembly can be seen at:
> <http://mbroker.tripod-dot-com/TeslaCoil/Electrode_holder_Prototype.jpg>http://
> mbroker.tripod-dot-com/TeslaCoil/Electrode_holder_Prototype.jpg
>
> (turns out the elctrode is 8mm, not 5/16", so they won't fit into the
brass w/o
> using a hammer, which I don't want to do just yet.)
>
> The holder is 1"Dx 2.10"long brass (don't know what kind - but it wasn't an
> "easy machining" type - lots of tool chatter).  The  "spacer" between the two
> "fins" is .50"D.  FTR, I'm going to remove the 45deg taper on the first "fin"
> of the holder.  I also have to tighten up the lathe a bit - too much play
which
> led to much imprecision.
>
> So, anyways, I was concerned about the .5"D brass being a weak point in the
> system (copper is about 5 times more conductive than brass).  I fear that if
> I'm operating a high power TC with a high bang size that the resistivity
of the
> brass will cause undue heating and I^2R losses.  I did some searching
> throughsome catalogs, and found at McMaster Carr a copper alloy that
appears to
> be the ticket item:  Copper Alloy 182.  It's virtually lead free, and
contains
> .6-1.2%by wgt chromium, which adds a lot of strength and high temperature
> stability.  The down side is that it's a LOT of money.  Alloy 172 also
seems to
> be a good bet as it's supposed to be spark-resistant, and even harder than
> 182.  I uploaded the PDF file explaining the alloys here:
> <http://mbroker.tripod-dot-com/TeslaCoil/3238.pdf>http://mbroker.tripod-dot-com/Tes
> laCoil/3238.pdf
>
> What are you thoughts on my design?  What are your thoughts on using this
> material for this purpose?
>
> Thanks, guys!
>
> Mark B