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Re: spark gap



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Adam,

Actually, they do both. For large high temp devices, they incorporate both mass and surface area. I have a Al heatsink here that is a good example (20" x 9" x 2") and used simply for high current transistor arrays. The fins mass gets larger with the need, but of course the fins are important for surface area. Aluminum is excellent for light weight, machinability, low cost, etc. There are better metals, but cost is an all-important determining factor.

Take care,
Bart

Tesla list wrote:

Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

For steady state operation, just look at how aluminum
heat sinks are constructed. They don't go for thermal
mass; instead they go for lots of surface area.

Adam

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Gerry  Reynolds"
> <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Bart,
>
> I think what you say is good.  Advantage of solid is
> high thermal
> mass. Advantage of tube is high surface area and low
> cost.  If
> cooling was such that air could flow axially down
> the tube as well as
> across the gap maybe thermal mass would not be an
> issue.  Seems like
> thermal mass only delays arrival of steady state
> temp and if cooling
> was enough to dissapate the generated heat at a
> reasonable temp then
> time to steady state may not be an issue.  Of course
> I havent tried
> this at 120ma  but at 60ma my hollow static gap
> never got warm.  A
> lot depends on how many segments one distributes the
> total gap over as well.
>
> Gerry R
>
> >Original poster: "Barton B. Anderson"
> <bartb@xxxxxxxxxxxxxxxx>
> >
> >Hi Tim,
> >
> >You'll probably get various opinions based on our
> experiences. For a
> >120mA NST, an SRSG would be of benefit. However,
> for a static gap, I
> >prefer solid vs hollow myself. I've found hollow
> gaps heat very
> >quickly and require quite a lot of air to keep
> cool. One down side
> >of hollow gaps is tap connection (it's hollow). A
> solid rod stock
> >gives the added ability to tap a hole in the end of
> each electrode
> >for connections. I'm currently running a solid
> brass gap and can run
> >it indefinitely with air flow. With the same air
> flow on a copper
> >hollow gap, I couldn't. It took a little time, but
> eventually the
> >sparks get shorter and shorter over time as the gap
> heats up and
> >lowers the voltage required to arc the gap. Static
> gaps are very
> >heat dependent for arc voltage stability. Probably
> the #1 issue. The
> >radius of curvature does play a role but good gaps
> can be built with
> >all the sizes you've mentioned with a 120mA supply.
> >
> >With that said, realize that hollow gaps have been
> the main focus
> >for years and is the majority of the lists
> experience with static
> >gaps. I guess mainly because of cost and easy
> access to copper
> >tubing. Mass is certainly helpful for heat
> dissipation and is even
> >typical for stationary electrodes on rotary gaps.
> The principal
> >applies, however, air is still required in either
> case and
> >definitely required for higher current gaps.
> >
> >Take care,
> >Bart
> >
> >Tesla list wrote:
> >
> >>Original poster: Timjroche@xxxxxxx
> >>I'm running:
> >>12kV 120mA NST
> >>.03 uF 45kV maxwell tank cap
> >>12 T .25" tube .25" spacing primary
> >>4.343" OD 28awg 17" lng secondary
> >>maj. dia 17" min dia 4" toriod
> >>
> >>What is the best place to start a static gap?  I
> have . 5" solid Cu
> >>(12 pcs. 4" long), .5" tube, 7/8" tube, and 1.125"
> tube...is hollow
> >>better? bigger dia?
> >>What about length? my 7/8" (6 pcs. 6" long) better
> than .5" 3"long?
> >>can you have to many gaps? i.e. total gap=.5",  2
> tubes?, 6 tubes?, 12 tubes?
> >>
> >>thanxs
> >>Tim
> >>
> >>
> >>
> >>