Re: Primary Resonant Frequency question . . .

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

Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>



Dan:

You really need to do the 20 turn "scrap wire" approach I mentioned earlier.
The most horrible thing you can do is have too little inductance in the
primary.  You usually end up with "racing sparks" as a result which could
damage your coil.

The "scrap wire" approach will keep you out of trouble.  It's very simple:
some old 12 AWG house wiring and 8 cardboard wedges with slots cut in them.
Scrape the wire bare for 1/2 in every turn and stagger the bare spots as you
move around the coil.

With NST powered coils we usually use something like 35 turns in our initial
test and usually around 20 turns with large coils.

Math is great but the potential for damage is far to great if you make an
error somewhere.

Best regards,

Dr. Resonance



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 17, 2002 11:39 PM
Subject: Re: Primary Resonant Frequency question . . .


> 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
>
>