Re: A double resonance solid state Tesla coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "K. C. Herrick by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>
 >
 > Several comments:
 >
 > 1.  Isn't magnetizing current associated with metallic cores?  A t.c. has
 > only an air core.

Magnetizing current in a transformer is the current that passes through
the primary winding when the secondary winding is in open circuit.
It is simply the primary voltage divided by the primary reactance,
for sinusoidal signals. It certainly exists in an air core transformer.

 > 2.  Is not primary current what we are after?  Lots of it and quickly?
 > Primary amperes x turns is what yields the magnetic flux and that flux is
 > all that the secondary "sees"--not, of course, primary voltage per se.
 > But a) impedance goes up as the square of the turns, thus exponentially
 > diminishing the current for the same voltage applied, and b) with few
 > turns and lots of current, resistive losses climb.  So what's the best
 > trade-off between amperes and turns?  I don't know...

What determines the speed of the energy transfer is the coupling
coefficient, not the impedance level of the primary circuit, that
is what you describe. For practical reasons, it is easier to have
a lot of primary energy by using a low-impedance primary circuit,
but this alone doesn't increase the speed of energy transfer.
Note that the magnetic coupling between the primary and secondary
is just one of the forms to couple the primary to the secondary.
A direct connection or a capacitive connection work equally well.

 > 3.  It seems to me that a series-resonant primary circuit would be quite
 > feasible provided that it were operated a bit off-resonance so as to
 > exhibit sufficient impedance to limit the current to what can be provided
 > by the driving source.  Or perhaps--the secondary will reflect sufficient
 > impedance back to the primary so as to accomplish that.  But there would
 > still be the problem that I see with all s.s. systems:  you can't hit the
 > primary with the relatively huge initial voltage available in a spark-gap
 > system.  That huge initial voltage delivers the relatively huge initial
 > current that, in the first few cycles, builds up the top-electrode
 > voltage above what it would be were the same total power delivered to the
 > electrode over many more cycles.  That's my conjecture, anyway...

Another problem is that a capacitor discharge system is ideally
lossless, while an active system, that is essentially a high-power
oscillator, dissipates a lot of energy in the active device.

 > 4.  All of the above may be largely conjecture since in 50 years I seem
 > to have forgotten more circuit theory than I ever learned.

This list is a good source of ideas to keep this knowledge in order.

Antonio Carlos M. de Queiroz