Re: Low Voltage Tesla Coils

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

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

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

The problem is that when the voltage gain becomes too high, the
inductance
ratio grows too, and a regular Tesla coil secondary would generate an
impossible primary coil.
Consider for example a coil with 500 kV maximum output voltage, with 50
mH 
of inductance.
With a maximum primary voltage of 500 V, the voltage gain is 1000, 
corresponding to an secondary/primary inductance ratio of 1000000. The
primary inductance would be just 50 nH. Not even a single turn of wire
at usual diameters.

A solution for this is the old induction coil, that operates with
low input voltages, stores the initial energy in a relatively small
but feasible primary inductor (or in a primary capacitor, much as in a 
Tesla coil, if operated by the dimmer+capacitor method), and obtains a 
large output voltage with a secondary inductor of very large inductance.
The system operates at lower frequency, mostly because the large 
secondary coil resonates with its own self-capacitance at a low 
frequency.

Antonio Carlos M. de Queiroz