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Re: Arc length vs pwr

Tesla List wrote:
> 
> >From wb8jkr-at-juno-dot-comWed Oct 23 22:15:08 1996
> Date: Wed, 23 Oct 1996 16:28:00 EDT
> From: Mark S Graalman <wb8jkr-at-juno-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Arc length vs pwr
> 
> >I'm going to have to disagree but I will measure it to see whether I
> >am wrong or not. I appreciate what you're saying, but you are not
> >feeding your series circuit with an external voltage source. The
> >capacitor _is_ the energy source and can only lose it from there, at
> >least that is what the scope says. Have you actually _measured_ the
> >voltage as climbing above what you initially charged the cap to? Once
> >again, E=0.5CV^2. Where does the energy come from that allows the cap
> >to go higher than it was initially?
> >     This consideration does not apply to the safety gap unless the
> >safety gap is bridging the capacitor itself since the safety gap
> >normally bridges rather low value stray capacitances.
> >
> >Regards,
> >Malcolm
> >
> 
>  The discussion had began in reference to a ringing
> primary with a very light or no load (under coupled or non coupled) like
> a secondary coil. Under conditions of
> load (coupling) the secondary coil looks like a series
> resistance to the primary oscillator loop. If resonant
> rise didn't occur a tesla coil couldn't operate, the
> principles of resonance apply if its a tesla coil or just
> a L-C circuit driven by a generator. The source of voltage in the primary
> circuit under condition of
> oscillation is the capacitor AND the inductor, the inductors back EMF is
> what charges the capacitor, the only reason we need the drive transformer
> is to get things started and to keep them going due to the limited
> Q of the circuit which is why the output rings down in
> level. Actually, I make take a big flame for this, but
> there is really no such thing as "parallel resonance"
> all resonant circuits are series in nature and operation
> series and parallel only really pertain on how the drive
> signal is applied to it. In order to be able to measure
> this resonant rise with any degree of accuracy you'd have
> to be very sure the measuring device offered VERY LITTLE
> capacitive or resistive loading.
> 
>                         Mark Graalman

Mark and Malcom,

Semantics often obscure discussion - this stuff is NOT simple, and
sometimes words aren't always up to the task...

1. Conservation of energy always applies to Tesla Coils:
In a capacitive discharge system, where the secondary fully rings-down
betweeen "bangs", once the gap fires the maximum amount of energy per
bang will never exceed 1/2CVgap^2. This applies no matter how we choose
to look at coupling, reactances, arc resistance, or series vs parallel
tank circuits. If the cap voltage EVER rose above this level, we would
end up with more energy in the system than we started out with - over
unity. 

This doesn't happen on Chip's list, NOR does it occur anywhere else in
the real world. :^)  Malcolm, you're correct.

2. You CAN see resonant rise on the primary cap if you power from an AC
source:
It' quite probable that tank cap voltages are _much_ higher than the
expected output from the supply. The tank capacitor forms a series
resonant LC circuit with the inductance of the HV power source. If this
is close to being "tuned" to the mains' frequency (50/60 Hz), the
steady-state voltage across the capacitor, and across the HV power
source, will rise to as much as Q*Vsource. This happens with ballasted
pigs, and it happens with neons. However, neons usually expire, where
pigs keep on tickin'.

The 50/60 Hz resonant rise blows caps and neons if not constrained by a
reasonable gap breakdown voltage that's _always less_ than the withstand
capability of either the transformer or the tank cap. A rotary's
variable breakdown voltage violates this condition, and the weakest link
lets out its smoke. A resonating 15 KV neon can generate 60-75 KV if not
"clamped" by the gap. Resonant rise in the primary circuit is NOT
essential for efficient TC operation. Since experienced coilers tend to
match the size of their caps to the power source, this effect is _very_
common (both the resonance and the smoke!). From a practical standpoint,
this drives us to conservatively rate the cap for at least 3-5X the HV
source voltage.

3. Resonant rise in the secondary-toriod IS essential to TC operation:
Mark, your point about resonant rise is absolutely correct for the
secondary circuit. The secondary inductance, toroid capacitance, and
secondary base ground-line form a series LC tank circuit that's
externally excited by the current flowing in the primary tank circuit.
Since energy is externally sourced from the primary circuit, resonant
rise occurs as energy is pumped into the secondary "tank". This occurs
for ALL primary half cycles of the first beat. (Malcolm's point about
having an external energy source applies here...)

As usual, flames and smoldering gap electrodes are welcomed!

Safe coilin' to ya!

-- Bert --