[Prev][Next][Index][Thread]

Re: Gap Dwell Times (formerly: Beating Solved)



<SNNIIPPP and a half>
> 
> Richard and all
> 
> OK, I hear you but..... I think they are called Oudin coils where the
> primary is the first few lower turns of the secondary. Suppose we use
> your super fast quenching gap and a secondary where the lower 5 to 20
> turns are the primary. Let us now dump into the "primary" some great big
> pulses and immediately quench the gap. we now have a bunch of energy in
> a two coil system with no place to go but "UP". I think we now have a
> 100% coupled system and a lot of energy in it. Why do we need resonance
> to get a transformation of this energy into the secondary...it's already
> there!
> 
> Thanks for your insight.
> 
> Skip

Skip,

Boy, you ask some very insightful questions! 

Even though the primary and secondary are electrically connected similar
to an autotransformer, they are still separate, loosely-coupled resonant
circuits from an energy-coupling standpoint. The coupling coefficient is
not 100% - it is still a small fraction (k). Because of the magnetic
coupling between the primary and secondary, this cannot be viewed as a
2-coil version of a base-driven resonator...

For terminology sake, the primary is the portion carrying the heavy cap
discharge current, and the secondary the remaining portion of the coil
plus the few primary turns. For simplicity, lets also assume that the
top discharge terminal's capacitance is significantly larger than the
secondary's self-capacitance. This lets us treat the secondary as a
coupled inductor instead of a transmission line (and greatly reduces the
"hairiness" of the explanation).

Initially, all the system energy resides in the charged primary
capacitor. When the gap fires, the primary's magnetic field builds, and
as the flux lines expand, some (but not all) cut through the secondary
winding. These induce a current in the secondary portion of the coil,
charging the coil's self-capacitance and top terminal capacitance. By
1/4 cycle later, all the energy in the system now resides in the sum of
the magnetic field around the primary plus the electrostatic energy now
stored in the secondary/terminal capacitance. However, the total system
energy is now less than we originally had due to gap and other losses. 

The secondary's energy at this point is only a fraction of that residing
in the primary. We would NOT want to try to quench the gap at this point
of maximum primary current - it would be an excersize in futility! The
more rapidly we tried to quench, the greater the voltage induced by the
collapsing field into the primary - most of the field's energy would be
expended in the gap with very little being transferred to the secondary,
although some horrendous voltage spikes might be created in the primary
circuit. Lets assume that we don't try to quench at this point.

The primary field now begins to collapse, inducing a current into the
secondary in the opposite direction as before. However, most of the
collapsing field lines intersect only the primary, recharging the
primary cap in the to the opposite polarity. The small fraction that
intersects the secondary pumps an additional increment of energy into
the secondary circuit. At the 1/2 cycle point, the primary cap is now
charged to a lower, opposite-polarity  voltage. At this point, the
primary current is now 0 - the first "zero crossing". We COULD choose to
do a "precision" quench at this point. However, look at where most of
the system energy resides: back in the primary capacitor! Not a good
situation for maximum energy transfer to the secondary!
 
Coupled resonant systems work best using properly-timed pushes, not step
functions, impulse functions, or sledge-hammer blows. By coupling some
of the primary's energy to the secondary during each 1/4 cycle, energy
transfers from the primary to the secondary in a delicate "dance" until
the primary's energy is expended. Quenching then "turns off the music",
and the dancers part company. 

Sheesh! One could almost wax poetic about this stuff... :^)

Safe coilin' to ya!

-- Bert --