# RE: Resonant cap?

```Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>

JT:

For DC operation, the capacitor size becomes an independent variable.
You can choose your cap size and then compute your Tesla primary
inductance that gives the resonant frequency to match the Tesla
secondary circuit.  So Xc = Xp gives 2*Pi*fr*Lp=1/(2*Pi*fr*Ct)
These should be familiar equations.
Fr is res freq - Hz
Lp - Primary Inductance - Henries
Ct - Tank Capacitance - Farads

You can try different values of capacitance and change the taps on you
primary to keep the same resonant frequency.

With only 10 ma, you will have a very small Tesla Coil.  I have one
output diode - so a DC system) to power it.  The flybacks are triggered
by a MOSFET.  The capacitor is 1 nF and and the Tesla Coils(I have two
180 deg out of phase) are 5/8" dia.  The toroids are doorknobs.  I can
get about 6 inch streamers between the toroids and about 3 streamers on
the toroid periphery.  I take this unit to my kids
school once a year for a demo.

You can see some pics at:

Http://www.teslaboys.com/TeslaMini/

Note the pics are a few years old.  They only show one coil and show a
single transistor driver for the flybacks.  I was able to push much more
power with the MOSFET.  The cap is a homemade parallel plate unit under
oil.

Mark Dunn

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Monday, January 29, 2007 12:04 AM
To: tesla@xxxxxxxxxx
Subject: Re: Resonant cap?

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

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?

>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>
>
>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.
>
>
>-----------------------------------------------------------------------
>------
>
>
>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.
>
>
>We won't tell. Get more on
><http://us.rd.yahoo.com/evt=49980/*http://tv.yahoo.com/collections/265>
shows
>you hate to love
>(and love to hate):
><http://us.rd.yahoo.com/evt=49980/*http://tv.yahoo.com/collections/265>
Yahoo!
>TV's Guilty Pleasures list.
>

_________________________________________________________________
Valentine's Day -- Shop for gifts that spell L-O-V-E at MSN Shopping
http://shopping.msn.com/content/shp/?ctId=8323,ptnrid=37,ptnrdata=24095&;
tcode=wlmtagline

```