Low Voltage Tesla Coils

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

I find myself pondering Low Voltage Tesla Coils - LVTCs (...sorry :o))))

We normally want high voltage to jump spark gaps and force RF currents
through big inductors that couple well to the primary.  However, IGBTs like
lower voltage but higher current...  You see where I am going...  With
IGBTs, everything is going to change...

There must be some optimal limits.  If we have a given secondary that is
probably just like the ones we use now, there must be a minimum primary
inductor (lowest firing voltage needed) that could couple at say 0.18 (or
just go for a low K auto quencher, but harder at high primary current...
But with IGBTs, maybe...)  Lower Fo's seem to be better for IGBTs which may
imply a higher number of secondary turns (thinner wire)...

If one thinks of using IGBTs for the primary "gap", everything changes from
what we are used to.  Imagine this...

A normal top terminal on a secondary coil.  The secondary has maybe 3000
turns to get the Fo frequency down to 75kHz.  A primary with a minimal
inductance couples to it at only k=0.12 (perhaps the secondary (for a low
inductance primary but still giving high coupling) should be an inverted
cone!! ;-)).  Being a DC driven IGBT coil, BPS is somewhat arbitrary (555
timer) at say 90BPS.  A very large value high current primary cap (just an
MMC with many short rows now), a small inductance primary coil, and an IGBT
gap.  High current but low voltage...

The voltage is easily in the range of MOTs (perhaps in parallel now) and
single or parallel IGBTs (since the voltage is low, series IGBTs and MOTs
are not needed now).  One may even be able to go down to ~300 or ~150 VDC
(line voltage just rectified) and eliminate that transformer!!  An Off Line
Tesla Coil (OFTC - sorry again :-)))

Many of the problems of an IGBT spark gap are due to the high voltage, not
high current.  Making a 25kV IGBT spark gap may be the wrong way to go.  It
may be much better to make a 3kV, or lower, IGBT spark gap and change the
coil to be optimal for that case.  The very expensive looking IGBT spark
gap suddenly gets 80% cheaper and in our range!!  If one could possibly get
the voltage down so low as to run directly off AC...  It boggles the
mind...  A 100 amp 208VAC three phase OFTC could push 36000 watts.
Considering that gap losses would be low, maybe twice the streamer power of
a conventional machine.

1.7 x SQRT(36000 x 2) = 38 foot arcs!!!!  From 100 amp three phase 208...
Without the need for a tranny, it might weigh 100 pounds!!  Maybe you could
send it UPS... :-))   Not even a spark gap motor anymore...

Sorry to ramble a bit, but I think something "big" is coming :-)))

Cheers,

	Terry

BTW - We need to somehow convince neon sign shops to buy big IGBT bricks
and throw them, still working, into big piles out back :o))))  Of course,
when the big bricks fail, you may still be able to use them since not all
of the silicon is blown...