Re: Inductive Kick Effects
> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
> Hi Terry, John, Malcolm, Richie, all,
> 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 xformer|s secondary is now drained.
> However, how can this energy enter the tank circuit?
There is none in the core at this time. However, there is an
equivalent voltage source sitting at Vpeak waiting to unload into
anything connected across the transformer terminals, in this case the
equivalent ballast inductance.
> 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.
It can do a bit of that and gap quenching can effectively knock that
on the head after the primary tank has gone quiet.
The inductor (xformer|s secondary) will try to
> resist the cut-off. I.e: it feeds it|s 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).
As Greg Leyh once pointed out, the charging current is but a
fraction of tank current.
> 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.
Agree. However, energy stored in the core is (IMHO) not huge because
dwell time is rather short.
> 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.
with (a) above depending on the primary cap value.
> 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 "it|s" 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 weren|t 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.