RE: electrode distance for stationary spark gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <gary.lau@xxxxxx>

Sorry, but I'm compelled to point out that this is bad advice.  Running
a coil with the gap opened up to the point where it won't fire is like
putting your car in neutral and flooring the gas.  Even if it does fire,
it may be at a voltage far higher than is safe.

A static gap acts like a voltage clamp, limiting how high a voltage the
capacitor will be charged to.  It's not immediately obvious, but this
voltage can build far higher than the rated secondary voltage of the
transformer.  If the cap is not discharged through the gap, the voltage
will build higher and higher on each mains half-cycle, through what's
called resonant rise.  The transformer secondary and the tank cap form
an L-C circuit, resonant in the neighborhood of 60 Hz.  Most folks these
days strive to use a cap value larger than what would be mains resonant
(i.e. LTR - Larger Than Resonant), but transformer core saturation and
ferro-resonance may conspire to achieve mains resonance none the less.

The only safe and reliable way to set a static gap is to apply only the
transformer across the gap (i.e. no cap in the circuit) and set the gap
width to just fire.  OK, maybe slightly wider if you like to live on the
edge.  As others have pointed out, there is no simple table that will
correlate gap width and voltage for any arbitrary geometry, especially
when using multiple gaps in series.

Regards, Gary Lau
MA, USA

> Original poster: Blake Hartley <teslaspud@xxxxxxxxx>
>
> Chistopher,
>
> I have started with two bolts that you can unscrew to make the gap
> larger. Start with a small gap and hook up the power supply,
> increasing the gap until there are no sparks, aand then pulling them
> back in a little. Even though this works, you are probably better of
> using a couple of pieces of copper pipe to form a multi-gap.
>
> Cheers,
> Blake
>
>
>  > I am trying to figure out how you determine how much of a gap
distance
>  > between two stationary electrodes should be? For a stationary spark
gap. Is
>  > there a formula ? All responses are appreciated :)
>  > Thanks
>  > Chris