# Re: Safety gap issues

```Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Jason,

At 03:55 PM 11/27/2005, you wrote:
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```YOU SAID:
"A very good equation that works well to find a coils peak output voltage is:

Vt = Vf x SQRT (Cp / (2 x Cs))

Where:

Vt it the peak top voltage
Vf is the spark gap firing voltage
Cp is the primary capacitance
Cs is the effective secondary capacitance
SQRT square root function "

```
* if i know the distance, can you tell me the sparkgap firing voltage? it is 7.5 to 8 mm, at 30MA. 8000v?
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Hmmm... I think you are using copper pipes in your spark gap so we will just assume they are about 2.5cm in diameter and use that data from this chart:
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Hmmm... That gives 25 kV peak which sound way to high for your 12000V NST... It would normally be about 12000 x SQRT(2) = 17kV. But your primary cap is near resonant so maybe you are getting a bit more... Hard to say without a high voltage probe and all... Lets just average the two ;-)
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(25 + 17) / 2 = 21kV That is probably as close of guess as we can make from here. So your coil is firing at about 21kV as far as we can guess...
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```* primary capacitance? you mean just the capacitor? 7.8nF (.0078 uF)
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Yes.

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```* secondary capacitance, with toroid, is 18.6 pF (.0000186 uF)

wtf? that means my coil only makes 117.3KV!!!!?   Cant be true. I wont buy it
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Vt = Vf x SQRT(Cp/2Cs) = 21000 x SQRT(7.8e-9 / (2 x 18.6e-12)) = 304kVpeak. that is probably pretty close. If everything we exactly perfect, that would give about 32 inch streamers. I think you said that yours are about 16 inches so maybe something is not perfect.
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You mentioned 8000 volts for Vf.  That would give:

```
8000 x SQRT(7.8e-9 / (2 x 18.6e-12)) = 116kVpeak and about 20 inches in a perfect system. It is possible the firing voltage is rather low but I would be super careful about trying to raise it. If something else is wrong, raising the firing voltage might blow the NST up...
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Most Tesla coils run in the 250 to 500kV peak range. There are a few coils that get past 1 million voltage but they are vary rare. Here is one a little under 2,000,000 volts ;-)
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http://www.lod.org/Projects/electrum/testing/pages/Levine23pwr.html

http://www.lod.org/Projects/electrum/index.htm

It is 38 feet tall!!!

Cheers,

Terry

```
```From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Safety gap issues
Date: Sun, 27 Nov 2005 10:02:21 -0700

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

A very good equation that works well to find a coils peak output voltage is:

Vt = Vf x SQRT (Cp / (2 x Cs))

Where:

Vt it the peak top voltage
Vf is the spark gap firing voltage
Cp is the primary capacitance
Cs is the effective secondary capacitance
SQRT square root function

This assumes the coil is well tuned and running well without any problems.
```
As far as I could ever tell, the size of the toroid really does not affect voltage that much. But larger toroids do have larger streamers. I think that is do more to electrostatic field effects rather than higher voltages.
```
Cheers,

Terry

```
```

```