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Re: Spark Gap Firing?

Original poster: Mddeming@xxxxxxx In a message dated 5/16/06 1:11:51 P.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes:
Original poster: "Tom Heiber" <tom.heiber@xxxxxxxxx>

When gapping the distance between electrodes. Should the spark gap
fire without the Tank Cap conected? How do you determine the optimum
gap distance?

From what I understand, the gap fires when the capacitor is charged
with enough energy to ignite the spark.
That would indicate that the gap should be set so that without the
cap, there would not be sufficient energy to fire up the spark, but it
should fire with the cap connected?



Hi Tom,

Almost all Tesla coils have a main gap and one or more safety gaps. The main gap can be static or rotary and safety gaps are always static. A safety gap is placed across the HV terminals of the transformer to prevent over-volting from missed firings or resonant rise from killing the transformer. A few folks also put a safety gap across the tank cap for the same reason. The transformer safety gap is set without the tank circuit connected. It is adjusted to be slightly wider than the setting that will cause an arc between its terminals and usually locked there. The main gap is never to be set wider than this distance. For a 15kV transformer this maximum value is a about 0.4" (~1 cm). It is voltage at the transformer, not power that determines the initial breakdown of a gap. Stored power will affect how long the gap stays conductive once breakdown occurs. There is no way to pre-determine the optimal setting for a given coil because the following all affect it to some degree:

1) Energy stored
2) Voltage across Cap at time of discharge
3) Temperature and Humidity
4) Surface condition of electrodes (smoothness, oxidation, temperature)
5) Electrode materials

Items 3 & 4 can change hour by hour or in some cases minute to minute.

Hope this helps

Matt D.