# Re: [TCML] calculate secondary voltage

```Hi John,

Even Tesla Coils adhere to Conservation of Energy (COE).

```
In a tuned lossless Tesla coil, Lpri*Cpri = Lsec*Csec. It can also be shown (from COE) that a "lossless" Tesla Coil will have a secondary-to-primary voltage ratio that is limited to no more than sqrt(Lsec/Lpri) or sqrt(Cpri/Csec)). The maximum output voltage versus the tank capacitor voltage when the gap fires (Vpri) for a lossless coil is:
```
Vsec ~ Vpri*sqrt(Lsec/Lpri)

```
In the case of a 12 kV RMS NST, the peak primary voltage may be approximated as 1.414*12 or about 17 kV. Under some conditions, it can be significantly higher due to mains frequency series resonance effects between the NST's current-limiting leakage inductance and the tank capacitor.
```
```
In order to reach maximum output voltage, the secondary toroid must also be large enough to prevent corona and streamers from breaking out and introducing secondary losses. In practice, heavy losses from the primary spark gap combine with winding and tank cap resistive losses to reduce the "no-breakout" output voltage to perhaps 75-85% of the theoretical maximum for typical spark gap Tesla Coils. You can plug in the measurements for your coil into JavaTC to gain a fairly accurate estimate of Lpri and Lsec, and then use 17 kV for Vpri to get a fair estimate of the theoretical maximum output voltage for your system. However, once streamers form, the output voltage will drop significantly below the calculated maximum output voltage.
```
Bert
--
Bert Hickman
Stoneridge Engineering, LLC
http://www.capturedlightning.com
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John Cooper wrote:
```
```My 4” secondary is wound with 26awg wire for apox 20”.  I figure this is aprox 1100 turns.

My primary is tapped at the 11th turn.

1100/11=100

NST is 12kv.

12kv X 100 = 1.2mv on the secondary?

john cooper
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```
```

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