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Re: Rotary Gap Electrodes - A first-hand experience



Tesla List wrote:
> 
> >From rwstephens-at-ptbo.igs-dot-netThu Oct 24 22:56:32 1996
> Date: Fri, 25 Oct 1996 00:36:36 -0500
> From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: Rotary Gap Electrodes - A first-hand experience
> 

> Brent,
> 
> Congrats on your spark length vs coil length.  Not shabby at all!
> I saw the pictures you posted on your new rotary gap.  Nice work!  I
> see you mounted your rotating 1/8th inch tungsten rods the same way I
> did with an allen setscrew into the side of a bolt head.  Damned good
> idea! : )
> 
> I don't think heavy heatsinks on your stationary electrodes is going to
> solve your problem.  Tungsten does not conduct the heat away from the
> source fast enough so a heatsink at some distance from the arc won't
> do the job.  A larger 1/4 inch diameter stationary contact will
> reduce the evaporization rate at the tips and also improve the heat transfer away
> to the heatsink, but I think you should investigate blowing high
> volume, high speed air jets past the ends of your stationary
> electrodes for forced cooling using a vacuum cleaner blower.  This
> also helps in quenching.  See pictures of my rotary with blown gaps
> on the funet.fi rws picture files.  I'm running a 0.125 mfd cap at 7
> kVa with this gap at 400 PPS in my MTC system without any trouble
> whatsoever.  Since those pictures were taken the stationary electrodes have been
> replaced with tungsten carbide pads brazed onto 1/4 inch steel mounting
> shafts.  The blower effectively cools the pads below the melting
> temperature of the brazing.  There is therefore obviously no
> electrode incandescence.  The first time this happened my electrodes
> would fall off.
> 

<SNIP>

> 
> regards,
> rwstephens


Just an update here -- I successfully lit up the coil (electrically...!!) tonight.
The 3/16" rods work OK, but after about 45 seconds, tips still heat to red-orange
temperature, and the ablation is still quite high.

The good news is that the coil is *really* humming! I do get a very nice spark
tone out of it now, and the wild, frantic discharges are a sight to see! Even
better, tonight's tests resulted in repeated strikes to a grounded object of 72",
which is 6" better than previous runs. (winding is only 22" tall!)

I am going to take you up on your suggestion about using a blower on the gap
electrodes. Tomorrow will find me on the road to C&H in Pasadena in an attempt
to find a good, high static-pressure blower. Nozzles will be fitted to the rotary
gap, and the air supply will commence via vinyl hose from the blower to the coil.

As a side note, I tried an idea which works quite well, and looks spectacular:
make a ring out of 1/4 to 3/8" copper tubing such that it sits about 1/4 the way
over the toroid. The sparks will break out all around the tubing and congeal into
only a few heavy streamers that move all around the toroid. The lower breakout
potential lowers the spark length a bit, but it sure looks fantastic.

- brent