Re: Electronic Ignition drivers for TCs/ which type is best?

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

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

Tesla list wrote:
 >
 > Original poster: "Jolyon Vater Cox by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 > When an ignition coil used to provide HV for a tesla coil it is good idea
 > to use electronic switch to turn the primary current on and off.
 >
 > One way use a 555 astable to gate the input of an electronic ignition 
driver.

A known very efficient method to destroy 555s, power transistors, etc...
Works, but if you look at the waveforms, there is a great possibility
that the 555 is being retriggered by the radiated pulses of the ignition
coil, and that its timing RC circuit is not doing anything...
(Ok, I know that with proper construction the thing works.)

 > Electronic ignition drivers come in two main types (i) inductive ignition
 > and (ii) capacitive-discharge ignition or CDI.
 >
 > Which of the two is best for driving a coil that is powering a TC?

Difficult to tell, since a diode in the circuit turns everything
into a nonlinear circuit. Probably indifferent.

 > My guess is that inductive ignition is better as it gives a longer duration
 > output spike which might be better for charging capacitors

No difference. The output, even without any load, is not a spike, but
a smooth almost sinusoidal pulse containing two widely separated
frequencies. Much as in a Tesla coil with (very) high coupling
coefficient. With a diode and a capacitor to charge, this waveform
will appears, approximately, only when the output capacitor is
fully charged, after several cycles.

 > maybe "inductive" nature of charging circuit better balances the
 > capacitance of the tank cap but I am not sure here. I do know that CDI
 > gives very short output spikes
 > -possibly not so good for charging capacitors- am I correct or incorrect on
 > this matter as I am currently using 555-gated Velleman K2543 inductive 
driver.

Look at the output, without sparking, using an antenna and an
oscilloscope, and you will see a smooth pulse with a high-frequency
ringing added to it. The frequencies are in the kHz range, usually.

Antonio Carlos M. de Queiroz