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Re: More RSG/cap queries


Bart, and sync-gap tesla coilers,

I while back,  when discussing sync rotary behaviour,  and
particularly the result of a missed firing,  I suggested
that the voltage rose to 41% higher than normal at the
next firing.

This figure was chosen to illustrate what happens for
two reasons:-

1) It was very close to what I saw when doing a simulation
   of a missed firing on a particular rotary gap,  with a
   particular capacitor,  and supply etc..  I really forget
   what the actual components were,  but the 41% "extra"
   voltage was fairly typical for that 100 BPS design.

2) I was trying to make the point that the energy pumped
   into the capacitor leading up to the missed presentation
   is preserved,  and is released at the next firing.

   If each bang occurs when the cap voltage is V volts, then
   the bang energy will be 0.5 x C x V x V.  At the bang
   immediately following a missed presentation I said the
   voltage was 1.41 x V.  Since 1.41 is the square root of
   2 this bang contains 0.5 x C x V x V x 2 energy,  which
   is twice the normal energy.  ie. It contains the sum of
   the energy supplied leading up to the missed firing and
   the energy supplied for one normal bang.

The actual process is slightly more complex than what I have
explained above,  since a missed firing does lead to some
variations in bang energies over the following 5 or 6 bangs.
A missed firing essentially "upsets" the system,  but it
quickly recovers due to regular electrode presentations, if
the gap is set correctly.

In a sync gap, the TIMING of the rotary dictates the TIMING
of the bang.  Because the charging circuit is resonant,
each bang energy is a complex function of many, many
parameters including supply volts, supply amps, capacitor
size,  and THE TIME SINCE THE LAST BANG.

If all is running smoothly then all of these parameters are
"constant" and the peak capacitor voltage will be even over
time.  If a firing is missed the capacitor has twice as long
to charge.

The 41% rise was offered because it has been observed in
simulations and makes the explanation a bit easier (Not much!)
(I have seen less than 41% and also much more, depending
on capacitor size, supply current and break rate.)

Also I would like to point out that all this assumes that
a safety gap doesn't "cut in" before the voltage rises too
high.  And we all use safety gaps in case the phase
is set incorrectly,  or in case there are several adjacent
missed presentations !

I hope this is a bit clearer,  since my previous reply was
somewhat rushed, (typed while at work !)

				- Richie

				- In sunny Newcastle