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William Howard wrote:
> are the primary and secondary oscillating at the same
> frequency or at a 1/4 wavelength?
Conventional Tesla coils all operate with the secondary
resonating in its '1/4 wave' mode. That's the coil's simplest
resonance, its lowest frequency resonance, and it has its high
voltage at the top.
An animation of the voltage along the secondary coil
http://abelian.org/tssp/cmod/mm3p.anim.gif
If you add another coil to make a 3-coil system, then it still
operates with a 1/4 wave resonance, but now at a lower frequency
corresponding to the 1/4 wave of the combined secondary and
tertiary.
Animation of a combined secondary and tertiary
http://abelian.org/tssp/acmq345-1.anim.gif
The junction between the two coils is marked by the vertical
line. You can see that it is basically the same voltage
distribution as a secondary resonating by itself, but now the
1/4 wave spans the length of two coils.
In either case you have to make sure the primary is tuned to
the 1/4 wave resonance of your secondary or secondary+tertiary.
> I get confused because I often see the 1/4 wave mentioned.
> JavaTC seems to supply numbers for a matched resonance.
It's really just a fancy name for a simple LC resonance, but
the name recognises that it is just one of many resonances
that the coil will do and refers to the coil's similarity to
a piece of transmission line.
JavaTC calculates the frequency of the 1/4 wave resonance of
your coil and its topload. You have to make sure you drive
it at that frequency and JavaTC helps with the primary circuit
calculations.
> I have been battling to get longer than 30cm arcs from
> my VTTCs.
30cm doesn't sound too bad. VTTCs are not known for having
really long sparks. Others on the list can advise better
than I on that subject.
Antonio wrote:
> Anything that can fit inside a sphere has less capacitance
> than the sphere ...
Indeed yes.
I borrowed an animation above, of your 3-coil '3:4:5' system.
Here are the next three resonant modes
http://abelian.org/tssp/acmq345-2.anim.gifhttp://abelian.org/tssp/acmq345-3.anim.gifhttp://abelian.org/tssp/acmq345-4.anim.gif
and the combined resonance when tuned almost correctly for
3:4:5 operation,
http://abelian.org/tssp/acmq.345.anim.gif
--
Paul Nicholson
--
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