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Re: Inductive Kick Effects
Hi Terry, John, Malcolm, Richie, all,
> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> Hi John, Malcolm, Richie, All,
> Well, I finally get it too! Richie sent me an excellent model that
>made the effect simple enough for me to understand too :-))
>Basically, the gap switching is changing the system from a
>resonant charging circuit to more of an inductive kick charging
>circuit. It is storing energy in the inductor and then the switching
>action allows a sudden high voltage kick right after the gap
>opens that charges the cap up to a higher voltage than
> the circuit would normally produce. This works much like those power
> supply ICs that switch current across an inductor to get -15 volts
>from +5 volts input.
And now....., I DONīT ;o)) get it anymore. How can the energy stored
in the xfomer be of help? Let me draw two schematics (use courier to
view):
1.Charging mode:
X--->------||-->----P
X P
X P
X P
X P
X P
X P
X----<-----------<--P
Current flows from the xformer (X) through the cap, primary
and then back to the xformer. I ommited the gap here,
because it is of no importance, as it isnīt firing, yet. So, we
now have a lot of energy stored in the cap, some energy
in the secondary of the xformer and very little (low ĩH)
energy stored in the primary.
2. Discharge:
X---> >------||-->----P
X | | P
X | | P
X o o P
X o o P
X | | P
X | | P
X-<-- <------------<--P
You will note that I have "installed" two gaps in the above
schematic and disconnected the xformer from the tank
circuit. As soon as the gap fires, (hopefully) all the energy
is fed into the priamary as our switch (= the gap) is now
closed. At the same time, the "second gap" (which is in
reality the same gap) also shorts the xformer. Any energy,
that was stored in the xformerīs secondary is now drained.
However, how can this energy enter the tank circuit? I think
(point out the error to me, please), the only thing this extra
shot of energy can/will do, is increase the time in which the
gap conducts. The inductor (xformerīs secondary) will try to
resist the cut-off. I.e: it feeds itīs energy into the still conducting
spark gap. This will increase quench time, which in turn will
not allow for a first notch quench (of which we do not know
if it is really necessary for nice long sparks). The voltage at
which the gap fires and accounts for the number of Joules
being "injected" into the primary is (mainly) a question of gap
spacing. I.e.: if the gap is set to fire at 15kV, the equation
0.5*V^2*C will give you the Joules. I can see no way in which
the voltage (and the Joules) will rise above this level. Of
course, I am ignoring the fact that a static gap will not always
fire at voltage "x", (due to preionization, etc) so there WILL
be variations, but not due to the energy stored in the inductor.
If the voltage "kick" that the inductor (xformer) produces, after
the gap opens, charges the capacitor up to firing voltage "x",
the bps rate (in a static gap) will increase. This might account
for the fact (i.e: the real mechanism behind it?) that one
actually can get a BPS that is many times Fmains in a coil
using a static gap. The statements above are made for a
coil using a STATIC gap.
If we now use a RSG, instead of a static gap, the picture changes
somewhat. The RSG can NOT "fire at will", so there indeed may
be a considerable voltage rise during the non conduction time. Up
to a certain point, this would mean the lower the breakrate, the
higher the voltage can rise, simply because there is more time in
between the breaks. If I am thinking straight, the voltage rise is
dependant on three things:
1.) The inductance of the xformer:
a.) The more inductance, the higher the possible voltage.
b.) The higher the inductance, the more time is needed.
2.) The quiescent time:
a.) The longer the time (up to a limit given by 1), the higher
the voltage can rise.
3.) The setting of the safety gap.
However, all this would also suggest to me, that each coil setup
would only be "happy" with "itīs" specific break rate, because
the xformer inductance (and primary cap) is different in every
setup. I remember John tried "ultra low" bps rates (60 bps)
and the results werenīt very encouraging. John, did you (or
could you) retry those experiments using once a xformer
with a low secondary inductance and once using one with a
high inductance. The setup with the high inductance *might*
benefit from the low bps.
Comments welcome.
Coiler greets from germany,
Reinhard