Hi Doug,
It's CRITICAL to understand the consequences of setting the spark gap too
wide.
It isn't obvious but the voltage that develops across the NST secondary can
FAR exceed the rated NST secondary voltage when there is a capacitor in the
circuit, and when this voltage exceeds the rated voltage, the cheaply-made
NST secondary insulation breaks down and shorts out, and short of messy and
heroic de-potting procedures, the NST is toast.
The width of spark gap sets a limit to how high that voltage can climb, and
discharges the cap when that threshold is reached. So the wider you set
the spark gap, the higher the capacitor will charge, and the NST sees
whatever voltage that is on the cap. Yes, performance of the coil will
always improve the wider you set the gap, up until the NST fails - a
terrible choice to make!
The spark gap width must be set so that with only the NST secondary (no
capacitor) across the gap, the gap *just* begins to fire. This sets the
breakdown voltage of the gap to the nominal rated secondary voltage. Any
wider than that and you're pushing the NST insulation beyond it's rating.
Regards, Gary Lau
MA, USA
On Thu, May 14, 2015 at 8:11 AM, Doug <doug11642@xxxxxxxxxxx> wrote:
> At what point is the spark gap too wide and what harm will result?
> Doug J.
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