# Re: Resonant cap?

```Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>

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I am just thinking of rectifying the output to DC now. It will make things much simpler. One problem arises though; how the heck does one determine the appropriate cap size, with a HV DC source?
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```From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Resonant cap?
Date: Sun, 28 Jan 2007 14:32:26 -0700

Original poster: Mike <megavolts61@xxxxxxxxx>

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That's where the 26.5pF came from, Gerry. JT, does it show on the ferrite any numbers? There are a few vendors of ferrite cores that you can look up the properties of ferrite materials. Perhaps it's possible to build a driver circuit that is a bit lower frequency...say 5 - 10 kHz which would allow you a larger resonant cap size. The only other suggestion is to rectify the output and use a voltage multiplying circuit to raise the output voltage. Then, you could fire your coil at whatever frequency you wish.
```Mike

Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>

Hi JT,

For your 30KHz transformer, the formulas that you want are these:

Zout = Vs_oc_rms/Is_sc_rms

Cres (nf) = 10^9 / (2*pi*freq*Zout)

use 30KHz for your frequency.  The assumption here is that the
winding resistance is insignificant compared to the current limiting
leakage reactance.  If you can measure the primary and secondary
winding resistance, we can verify the assumption.

Gerry R.

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For the...thrid time now, online calculators only work for
50/60Hz.......

My Transformer runs at 30kHz, 2KV AC, 10ma.

Again, you cannot use an online calculator in this case. Go back to
deep fried neon. Look above where you put in the voltage and current.
It has a selection for"50 Hz" and "60Hz". NO 30KHZ.

So far, I have only received one real response; 26.5pF. I calculated
by hand and received a similar answer. I need some more opinions
though.

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