Re: ALF prototype work, RTC tests

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Greg,

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.

Gerry R.


 > 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:
 > http://www.pupman-dot-com/listarchives/1998/january/msg00059.html
 > For this test, the energy spent two full amplitude cycles in the
secondary,
 > 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
or
 > 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
primary
 > 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
 > available.
 >
 > 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
units]
 > 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.
 >
 >
 > -GL
 >
 >