[TCML] Spark gaps (again)
deano at deanostoybox.com
Wed Mar 4 21:42:59 MST 2009
On Wednesday 04 March 2009 07:52:58 pm otmaskin5 at aol.com wrote:
> I've been following earlier discussions about higher losses associated with
> multi-segmented spark gaps (i.e., Richard Quick type) compared to a single
> gap. It's clear that the experience of this group has been power losses
> are significantly less with a single gap style with adequate airflow. But
> I'm not sure I caught why that is. What is the reason that a 0.27" single
> gap loses less power than an 9-gap / 10 pipe RQ gap that has total gap size
> of 0.27"? If total gap spacing is the same for both, why would one be more
> lossy than the other?
I'll take a stab at this. Let us say for the sake of argument that we have two
gaps. Gap one is composed of two 1" copper pipes 0.27" apart. The other is
composed of ten 1" copper pipes 0.03" apart. That is nine gaps of 0.03" for a
total spacing of 0.27", same as the first gap.
Now let us assume for the moment that an air gap of 0.27" will behave exactly
the same way whether it is a single gap, as in the first case, or nine shorter
gaps added together, as in the second.
Note that the copper pipe heats up where the arc/spark touches it. Just a little
spot gets hot, but it heats up nevertheless. The heating of the spot is the
same on both sides of the arc/spark. The heating of the spot, that is how much
energy is consumed by the heating of the spot, depends on the current flowing
in the arc/spark. It is a loss (I^2R) representing resistance.
In the first case with the single gap we have two spots. In the case with the
nine gaps we have 18 spots. So 9 times the resistance in the interface between
metal and spark. Nine times the energy wasted heating metal. More total
resistance in the gap.
Of course in the real world air gap of 0.27" will NOT behave exactly the same
way whether it is a single gap, as in the first case, or nine shorter gaps
added together, as in the second. The arc/spark heats the air too. It is easier
to blow away nine little spots of hot air than one big one.
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