# Re: SSTC does 10 foot sparks

Original poster: Sean Taylor <sstaylor-at-uiuc.edu>

Hi Matt,

I agree with what you say, to a point.  First, I was simply refuting the
statment that efficiency based on power doesn't make sense (loosely
paraphrased).  It is hard to determine the "efficiency" of a TC, since as
you say, it is quite a dynamic machine.  What I did/would suggest, if one
were interested in the strict efficiency (and it was possible to measure
the output easily), would be to use an energy type of approach as I said
about a single shot mode.  However, this doesn't really apply to streamer
growth which happens over successive bangs and doesn't have a predictable
pattern - ie "the streamer will be at 85% of the full length after exactly
14 consecutive bangs".  There is a lot more that comes into play, and I
think an average power approach compromises enough in order to include
enough of the fluctuations.  Of course, there isn't a really good way to
measure the output power of a TC, so we end up using streamer length
frequently, and end up with no "real" units of efficiency, but rather a
performance "guideline".

As has been stated many times implicitly, and now I'll make it explicit,
(in my opinion) and energy measurement is useful for an isolated,
controlled instance.  The power measurement will cover a more continuous
timeframe and does not consider the amount of time so much as the rate of
transfer.  This is evident in the units - energy is N-m (- meaning
multiplied), while power is N-m/s.  Power is just a rate, like m/s, and
doesn't give a specific quantity, but rather an idea of how fast you're
getting to a specific quantity.  I suppose one could frame the question of
power as "How long does it take for a TC to transform X kJ of energy (into
another form)?".  Anyway, enough of this topic :-)  I think I and others
have probable done as much to confuse the issue as we have to make any more
sense!

Sean Taylor
Urbana, IL

>Hi Sean,
>Power makes sense for the devices you cite, but only because they are
>fairly constant and continuous power-in, power-out devices with a load
>that can be held constant during testing. None of this applies to a Tesla
>coil. The input and output occur at different times, are of different
>durations, different waveforms, different frequencies. In this case, a
>good argument for energy measurement can be made.
>
>Matt D.
>