Re: Low Voltage Tesla Coils

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

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

Hi Antonio,

I ran some MicroSim models tonight trying to get a TC to run at 700VDC and
I had BIG problems as you suspected...  The basic physics is saying that it
is not going to work at 700VDC...  We probably have to use MOTs to get to a
higher voltage to be able to use practical primary coils.  that suggests a
voltage of about 3000 volts at least, so we have to do some stacking of
"ordinary" IGBTs.  Still far better than 25kV of them, but the "off-line"
idea seems doomed :-(((  Golly, that would have been so cool.....

You inductance storage idea needs much further thought!!!!

We may be able to use caps and diodes to pump the voltage higher but that
only works so far before some type of "big iron" is needed.

Cheers,

	Terry


At 10:52 PM 7/13/2002 -0300, you wrote:
>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
>
>