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Em 03/02/2014 07:46, Udo Lenz escreveu:
Yes, measurements indicate that capacitive and resistive arc loads are
roughly of equal magnitude, i.e. a phase lead of about 45 degrees of
arc current to arc voltage. For fast growing arcs it is more like 60
degrees.
I have two primary circuits that I can use with my secondary and driver.
One has high impedance, 5 nF and 58 uH, and another has lower impedance,
22 nF and 14 uH. With the first system I don't have breakout at the
secondary. Tuning the system between the resonances, without feedback,
the measured output current shows a series of complete beats, with
slowly decreasing amplitude. With the nominal design for 10 cycles for a
full current beat, I see two beats with 10 cycles with the driver set to
produce between 10 and 20 cycles (energy going out and back in). With 30
to 40 cycles I see four beats. With 50 to 60 cycles I get six beats, and
so on. The amplitudes of the beats decay slowly due to losses. This
agrees with a linear model. If I tune the driver at the resonances, I
get ramps of increasing current until breakout occurs. A breakout point
results in essentially the same behavior, with small streamers with the
tuning between the resonances and longer streamers with tuning at both
resonances. Too long bursts don't increase the streamers beyond a limit,
due to detuning.
With the low-impedance primary there is an important change. Tuning
between the resonances I get breakout easily. If I just extend the burst
length I see that the primary current increases as a kind of ramp after
a first beat, and streamers grow with burst length up to a limit caused
by detuning. If I tune at the resonances, I get less impressive results
and much larger primary current.
So far I am confirming my idea that tuning between the resonances leads
to a more efficient drsstc, even with breakout and longer bursts than
the minimum. But the voltage peak at the end of the first current beat
must be enough to start significant streamers.
Maximum output voltage is not necessarily decreased. More energy in the
primary tank leads to a higher magnetic field if the geometry isn't
changed.
That would imply more secondary voltage.
Surely. But the energy stored in the primary circuit without current
beats is mostly wasted. I am still insisting on at least a first beat,
extracting the energy in the primary circuit to start streamer
formation, as happens in a conventional Tesla coil.
The question of arc length versus voltage is indeed difficult. Arcs of
shorter
duration need more voltage for a given length. Also I believe, that
higher
TC frequencies require less voltage but more power.
The question of the effect of frequency is also obscure.
About the problems of my coil, I made a better GDT, but the performance
was practically the same. My complicated idea of a GDT with a
center-tapped primary is complicating my driver (The idea is similar to
what is used in PC power supplies to drive a half-bridge of bipolar
transistors). The strange 1 MHz oscillation persists, but appears only
when sparks are drawn. The oscillations occur between a pair of bursts,
and not always. Something as
|-------|ooooo|-------|-------|ooooo|-------... (|=burst, o=oscillation,
-=wait time). A ferrite core in the bridge output suppresses the
oscillations, but the driver output voltage becomes quite strange.
Probably the oscillation occurs just when I connect the oscilloscope.
I am seing also high-frequency oscillations in the bridge output voltage
when energy returns (free-wheeling diodes conducting).