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Re: rotary gap electrodes

Tesla List wrote:
> 
> >From chip-at-poodle.pupman-dot-comSun Aug 18 22:10:04 1996
> Date: Sun, 18 Aug 1996 21:43:19 -0600 (MDT)
> From: Chip Atkinson <chip-at-poodle.pupman-dot-com>
> To: Tesla List <tesla-at-poodle.pupman-dot-com>
> Subject: rotary gap electrodes
> 
> Greetings,
> 
> I'm asymptotically approaching the state of rotary gap construction known
> as completion.  I thought I would ask for others input before proceeding.
> 
> The design of my rotary has two 1" thick 14"x14" pieces of plexiglass to
> hold the bearings and act as side shields.  The stationary electrodes are
> going to be mounted to the plexiglass and poke into the box where the
> disc is rotating.  I am using 1/8" tungsten TIG welding rods for
> stationary electrodes.  The input power will be less than 10KVA.
> 
> My questions are: How much cooling of the stationary electrodes do I
> need to do?  Will putting the W (tungsten) rod into a piece of 5/8" brass
> rod 2" long be enough to prevent the rod assembly from getting so hot
> that it melts the plexiglass?  I have also considered some sort of
> non-thermoplastic insulator to surround the brass.  Another option is a
> 1" rod of Al with the W rod in it.  The Al could have cooling fins turned
> on it too if necessary.  I don't figure ohmic heating will be much of a
> factor, but the arc will be hot and so heat the electrodes.
> 
> Any input would be appreciated.
> 
> Chip


Chip,

Mount no electrodes in plastic ever!  You will never cool them fast 
enough!!!  The electrodes must be in metal rods mounted in metal holders 
on fiber glass.  If one of the electrodes started melting the plexiglass, 
it could melt into the churning rotor and LOOK OUT!

I use .180  dia. W electrodes monted in aluminum rods 5/8" in diameter on 
maggy 11's series rotary gap.  They are captured by aluminum mounts which 
are themselves mounted on heat resistant fiber glass.  They get so hot 
(~700 deg F)  that they dis-color the fiberglass two inches away from the 
rod!  I use about 5-8KW normally.  I have used 10KW on this gap once or 
twice and the Tungsten got almost white hot on the tips and a white ring 
of flame was seen as the gap spun.  (It had reached its limit)  I would 
limit your gap and system to about 5-7KW with 1/8 W rod electrodes.  The 
fan action of the rotor will cool about as good as an auxiliary fan.

Richard Hull, TCBOR