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Re: ALF prototype work, RTC tests
Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net>
Could you refresh my memory a little? Is the ALF project a twin coil
project where each coil reaches about 150 foot high and the two coils are
300 foot apart and expected to produce 300+ foot arcs at 5.5MWatts?
If so, where is the full scale prototype being built and what power are you
planning on feeding the 1:12 scale prototype.
> Original poster: "Greg Leyh" <lod-at-pacbell-dot-net>
> Hi All,
> I'm resuming work once again on the 1:12 scale ALF prototypes.
> Assembled one primary/secondary/toroid set, measured Fres and set the
> coupling. Put some HV to the finished driver [only 2kV to start] and
> measured the intra-coil dynamics, and tested the gate control circuits.
> Rep-rate 4Hz max, as the test charging supply is small. Pulse waveforms
> appear normal, looks quite expectedly like two coupled resonators. No top
> breakout at 2kV drive, though there's lots of secondary electric field;
> open scope probes see ~100V.
> However, the most satisfying bit came from testing the 'secondary energy
> recovery' concept, that I mentioned briefly a while back in this post:
> For this test, the energy spent two full amplitude cycles in the
> before returning to the primary capacitor. The IGBT then commutated the
> primary current to the diode and turned off in about 1uS, trapping the
> energy in the primary. Approximately 1650V of the original 2000V was
> reclaimed, or about 68% of the original energy. This percentage will of
> course be lower once there's significant streamer action, but the general
> concept appears to work.
> Why would one wish to recover the secondary energy after only a few
> cycles? Current measurements on Electrum indicate that only the first 2
> 3 cycles of full secondary voltage contribute significantly to dart leader
> production; once the amplitude decays by a relatively small amount, the
> spiky dart-leader currents disappear, leaving only the normal reactive
> capacitive currents. In a standard TC, this remaining unusable energy
> would remain trapped in the secondary, eventually ringing down to zero --
> lost to the secondary copper and the surrounding air. But now that
> switches are available that can fully quench in less than a half cycle,
> this energy can be successfully recycled.
> Historically, traditional TC designs haven't needed to bother with this,
> for two reasons:
> A) Overall efficiency is not a major issue for most coil applications.
> B) Primary switches with suitable quench performance were not readily
> However, the heavy AC power requirements for the *full-scale* version of
> the ALF [about 5.5MW] will absolutely require some form of energy recovery
> for economically viable operation. The ALF 1:12 scale prototype will
> feature this regenerative energy control scheme as well, for further study
> and refinement. At the risk of saturating the list with yet another
> acronym, I'll propose that this recovery scheme be referred to simply as a
> Regenerative Tesla Coil, or RTC.
> Most of the key components [secondaries, toroid parts, primary drive
> for the 1:12 scale prototype are now complete, awaiting final integration
> and testing. Depending on workload, I'll try to get some waveforms and
> pics up on the lod-dot-org site around Thanksgiving.