Dear Steve,
This explains perfectly the problems I have been having.
It also explains why using a tickler coil that is a few extra turns at the
base of the secondary leads to easier tuning (for myself). I had problems
with the tickler coil resonating with the primary and a lot of head ache
with positioning it.
One further question: at higher frequencies the tank capacitance is smaller
does this impact on the amount of 1/2 rf cycles needed to transfer energy?
I read somewhere that the longer the energy takes to transfer (ring up) the
longer the spark length.
I started out with VTTC building by reading your FAQ. It was and is a very
helpful and informative reference and I thank you for taking the time to
write it!
I will give that software a go and adapt an equivalent circuit for the
magnifier as the model. I found this circuit in an article covering triple
resonance and it covers mutual capacitance and inductance.
Cheers!
-Wil
On 14/08/2014 7:11 AM, "Steve Ward" <steve.ward@xxxxxxxxx> wrote:
> Wil,
>
> Java TC is fine and calculating the resonant frequencies of coils, however
> it does not tell you what frequency that the coupled coils will resonate at
> together. Because there is a mutual inductance between the coils, the
> operating frequency will be somewhat different than the resonant frequency
> of either the primary or secondary. The field of the 2 coils can add,
> resulting in a lower operating frequency than the resonant frequencies
> (often referred to as the "lower pole" mode), or the fields can cancel and
> the operating frequency will be higher than the Fres of either coil (upper
> pole mode). The coupling coefficient determines the mutual inductance, and
> consequently how far away the operating frequency will be from the
> "resonant frequency".
>
> I suggest using a circuit simulator like LTspice (which is freeware), and
> making a model from the Ls and Cs that javaTC reports. From here you can
> run an AC sweep analysis and spot the possible operating frequencies, which
> show up as peaks in the response (this is where the term "pole" comes from
> as the frequency response has distinct peaks that resemble something like a
> circus tent held up by a pole).
>
> Richie Burnett has a good write up about frequency splitting, which is the
> same phenomena im trying to describe:
>
> http://www.richieburnett.co.uk/operatn2.html#splitting
>
> The only real distinction to be made about a CW coil is that you are not
> exciting both pole frequencies (like a SGTC does, for example, and the
> result is a beating waveform... the sum of 2 frequencies). CW coils will
> "settle out" at one pole or the other, depending on tuning and how the
> circuit operates.
>
> As to what frequency produces the longest sparks, thats a really tough
> question. Higher frequency operation produces a hotter arc which can grow
> longer for a given voltage, however its not free lunch since efficiency
> often drops at higher frequency operation due to resistive loss, and losses
> in the tube. Id probably go for lower frequency operation if larger sparks
> were the target, mainly to get the efficiency up so that more power could
> be processed before melting down.
>
> Steve
>
>
> On Tue, Aug 5, 2014 at 11:56 PM, William Howard <snakeprior@xxxxxxxxx>
> wrote:
>
> > Dear Group,
> > I'm having a dreadful time tuning my VTTC. I have been using Java TC as a
> > guide for primary turns and using multi taps.
> >
> > My question is: is Java TC calculator accurate for CW Tesla Coils or
> would
> > the frequencies be different?
> >
> > Further more what is the best frequency for spark length? I've noticed
> the
> > spark becomes shorter and more flame like above 1mhz until 6mhz it
> becomes
> > a flame.
> >
> > If I were to design the optimum system what resonant frequency of the
> > secondary should I use to get the longest CW spark?
> >
> > Cheers!
> > -Wil
> > _______________________________________________
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> > Tesla@xxxxxxxxxx
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> >
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