Re: Primary Resonant Frequency question . . .

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Dan,

Tesla list wrote:

> Original poster: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>
>
> Quick question:
>
> I've measured the resonant frequency of my secondary / toroid assembly and
> it turns out to be 195 kHz which is much lower than what i calculated in my
> designs.  Using tesla coil cad program, it says with my current primary, i
> should be tapped between turn 13 and 14 using a NST of 15kv/60mA, a 0.0106uF
> capacitor at 195kHz.  Basically, this says i'm screwed, because in my
> original calculations the resonant frequency was around 225kHz and needed to
> be tapped between turn 10 and 11.  I'm screwed because i only have 12 turns
> (oops . . . ) of my primary.

Top loads will "always" lower the resonant frequency of the secondary. The
toroid should always be accounted for
regardless of what program your using (including hand calcs). Your in luck!
Terry Fritz wrote a program quite a
while back known today as E-Tesla6. Use it to find how the top load affects
the resonant frequency. Once you use
E-Tesla6 to determine the frequency, regardless of which program you use,
simply vary the toroid size until the
programs frequency matches that of E-Tesla6 (then and only then can the
primary turns be determined within a small
percentage). This works because the programs are nothing more than
calculators attemting to determine the total
capacitance of the resonator. Otherwise, always wind more turns than you
"think" you'll need. JavaTC has an input
called "Reduction Percent" which is used exactly for this purpose (prevents
have to change the toroid size for the
C adjustment).
For reference, here's E-Tesla6:
http://www.hot-streamer-dot-com/TeslaCoils/Programs/Programs.htm

One other point. All these programs are using the lumped capacitance of
secondary and topload. So the capacitance
reduction is really a percentage taken away from the lumped capacitance.
The topload reduction just makes an easy
avenue to perform this function.

> My question, is that I'm using a SRSG with a LTR capacitor of 0.0275uF
> instead of the 0.0106uF.  Does this change my resonant frequency
> calculations at all????

It changes the primary tank circuits natural frequency. Adding C reduces
the number of turns required to match the
secondary's frequency. It might work out just right for you.

> Also, other than changing my topload, re-doing my primary, is there any
> other way to increase the resonant frequency of my secondary assembly???

The "main" components (LC) for the secondary are contained in the winding
and geometry. Obviously, adding or
removing turns will change the frequency. External to the secondary is the
top load. Change it's size or position
and you change the resonant frequency to some degree. This is why the
primary is typically built with a few turns
more than needed to account for various influences.

Take care,
Bart