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Re: How many gaps is too much?
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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: How many gaps is too much?
> Date: Wednesday, February 12, 1997 1:25 AM
>
> Subscriber: tesla-at-america-dot-com Tue Feb 11 22:56:01 1997
> Date: Tue, 11 Feb 1997 07:14:41 -0500 (EST)
> From: Bob Schumann <tesla-at-america-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: How many gaps is too much?
>
> Howdy all,
> Maybe I am mistaken but did Tesla say something like
> that you could never have too many gaps?
>
> I was thinking of making a stationary spark gap but to have
> many of them which will bring the distance between any given
> 2 gaps closer as the number of gaps increase. I think that by
> having many more gaps, you would have a better 'resolution'
> so to speak when adding in or taking out gaps.
>
> Thanks is advance
> Bob Schumann
Bob,
Yes, increasing the number of gaps is generally useful.
In many cases it is much better to have many small gaps rather than one or
two large gaps. Part of the reason has to do with the temperature of the
gaps. When you use only a single gap, it tends to overheat, you get metal
vapor adding to the ionization, and it tends to fire irregularly. Many
small gaps (especially if the striking surface is large and rounded, as in
the Richard Quick Gaps) are easier to keep cool, and the eventual breakdown
is more regular.
It is often useful to have more than one series type spark gap. Part of the
reason is that cooling arrangements are more efficient that way. The air
used to cool a set of gaps comes in cool and leaves much warmer. The more
gaps you have to cool, the warmer the air is. If the air at the end gets
too warm, then at least some portion of the gap set will be too hot and may
cause unwanted ionization. If the cooling air can be drawn through the gap
itself, this also helps, as the quenching action is thus increased. Many
people have found that sucking the air through a gap is more efficient than
trying to blow the air through it. A vacuum cleaner is the usual source of
negative air pressure.
The spark gap is a key element of the Tesla coil. Its design should not be
an afterthought. The spark gap should be designed for maximum power. That
means keeping the materials that form the gap large in striking surface
area. Multiple gaps do this quite well. The heat must be removed rapidly so
the gap material is kept cool. Use of finned and large surface area
electrodes facilitates the heat removal allowing us to use air at lower
pressures. The Gap conducts tremendous peak currents. It is useful to keep
these paths as straight as possible. This is one defect that I see in the
Quick Gap that is built into the plastic pipe material. Although this
design facilitates cooling, you *have* introduced about a 3/4 turn, and
though many might not think of that spark gap as being a 3/4 turn coil, it
*IS*, and that will limit a bit the current that will ultimately be
delivered to the primary.
Mark Hammer has a variation on the Quick Gap that has all the elements
lined up in a straight line (as far as the arc and current path go). It
makes the Spark Gap larger, but cuts down on its inductance. If properly
enclosed in a container with open sides and fitted with a couple of fans,
this design is slightly better than the original.
With all of these multiple gap types, it is useful to have a means whereby
one can strap out a gap or gaps so that the effective gap legth can be
somewhat adjusted.
Fr. Tom McGahee