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# RE: How (does) voltage rise(s?).

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• Subject: RE: How (does) voltage rise(s?).
• From: "Tesla list" <tesla@xxxxxxxxxx>
• Date: Mon, 17 Jan 2005 08:43:44 -0700
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• Resent-date: Mon, 17 Jan 2005 08:44:10 -0700 (MST)
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`Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>`

`Hi Chip,`

```Your explanation sounds fine to me. But I would like to add just one little
point. You said-```

```>Why not just have a solenoidal primary enclosing the
>entire secondary rather than a pancake or conical primary?```

```Well a TC with this configuration might not necessarily be a bad thing. It
seems in practice that with solid-state coils, the tighter you couple the
primary and secondary, the better it works. In fact a coil with a coupling
of unity might even give a higher output voltage than one with lower
coupling. To take an example, I have one coil that has a single primary turn
driven by a 1kV source, and 1500 secondary turns. If k=1 you might expect
(1000v in * turns ratio of 1500)= 1.5 million volts output*. But in practice
I designed for a coupling of 0.15 and I only get about 600kV.```

```BUT (and this is the big BUT) if you have the primary too close to the top
of the secondary, then the high voltage just arcs over to the primary
instead of making proper streamers.```

```This (IMO) is what limits the coupling we can use in practice. That, and the
finding that with classic spark-gap coils, too tight coupling can cause
racing sparks. The relation between coupling and racing sparks doesn't seem
to hold for any kind of SSTCs I have seen, so we use tighter couplings on
these.```

```* assuming the secondary had no capacitance (which is not very realistic) If
it has capacitance such that L1C1 = L2C2 then I believe the peak output
voltage is half what you would expect, so 750kV in this case.```

`Steve C.`