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# Re: [TCML] multiple coils at same time off one NST

```On 7/25/18 1:59 PM, Matthew Sweeney wrote:
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```How is that possible? With my limited knowledge I would assume this would
be quite difficult, what with impedence matching and all that. Wouldn't the
spark gaps interfere with each other?

I would be very interested to know more.

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I would assume that basically the NST acts as a constant current source.

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In one standard configuration (the one I use for NSTs on a single coil) it's
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Transformer - spark gap across transformer - series Cpri and Lpri

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So when the gap fires, Cpri, Lpri, and SG form a resonant circuit that rings down.
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If you ganged up two coils this way, they'd fire at the same time, but the two resonant circuits would only share the spark gap. there's no particular reason why the two coils would have the same resonant frequency.
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The transformer would be charging both Cpri in parallel, so the charging rate is essentially halved (if the Cpri are the same)
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In the other configuration (more like a DC resonant charging circuit), the transformer is across the capacitor, and the spark gap connects between Cpri and Lpri.
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This one would be harder to analyze - the two coils share the same Cpri, and presumably, one gap would fire before the other, and the other would never fire, but if it happened to be "lucky", you might get alternate firing of the gaps (or you could use a triggered gap?)
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If the "ringdown" takes, say, 10 RF cycles at 100kHz, that's 0.1 milliseconds. That's much shorter than the time to charge the primary capacitor (depending on where in the line frequency cycle you are), so you could conceivably charge the primary multiple times in a half cycle, and fire the gaps more often.
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(Assuming you're "smaller than resonant" sized Cpri)

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