Re: Energy storage in primary?

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

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

HI Terry,

On 28 Jan 2003, at 12:52, Tesla list wrote:

 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Malcolm,
 >
 > Yes!!!  A car ignition coil may be the perfect coil for this.
 >
 > One would have to use say a GM HEI coil with the core cut away to get a
 > "true" loosely coupled Tesla coil.  Then an electrode could be added and a
 > suitable cap found for the primary that would tune the system.
 >
 > Unlike the GMHEICSLR thing, current would be the main driver.  So the gap
 > would be replaced with say an IGBT and a current source (only a few amps
 > now, a plain battery...) would drive the system.
 >
 > I worry a little about the voltage kickback, but were only starting with a
 > few amps so maybe it would not be too high for say a 1200V IGBT.  I would
 > think such a system could easily get to Jolyon's 6 inch
 > requirement.  10kHz, 3 amps, ??? inductance, 1.7uF capacitance...

If the "primary cap" is placed across the switch it would limit the
risetime of the waveform and the switch should not be at all troubled
by inductive kickbacks. I've driven cored ignition coils with
bipolars and it's commonly been done in car ignition systems. I like
the idea of removing the core. It would decrease the necessary dwell
time to hit a given primary current considerably. It should be a very
workable scheme to get 6" from a well-built and insulated coil. Just
how reliable a GM coil might be under continuous repetitive
conditions is an interesting question, especially if air streamers
are allowed.

Regards,
malcolm

 > http://www.powerlabs-dot-org/gmheicslr.htm
 >
 > Cheers,
 >
 >          Terry
 >
 >
 > At 08:24 AM 1/29/2003 +1300, you wrote:
 > >Hi Jolyon,
 > >
 > >On 28 Jan 2003, at 8:01, Tesla list wrote:
 > >
 > > > Original poster: "Jolyon Vater Cox by way of Terry Fritz
 > > <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 > > >
 > > > Is it possible to build a TC where energy is stored initially as high
 > > > current in an inductor (the primary) rather than high voltage in a
 > > capacitor?
 > > > I am thinking of a setup where current ramps up slowly through the
 > > inductor
 > > > before being abruptly switched off (by semiconductor switch or similar)
 > > > after a predetermined current or period of time has been exceeded; the
 > > > current in the primary rising and falling as "saw-tooth" waveform.
 > >
 > >Exactly how a car ignition coil works.
 > >
 > > > As primary input power for this would be largely determined be current
 > > > rather than the voltage of the PSU
 > > > how high would the current have to be/ how low could the voltage be for
 > > > decent spark output say, a minimum of 6 inches or more?
 > > >
 > > > For the control logic would this likely need an exotic switch-mode power
 > > > supply IC with PWM and dead-time control or could a simple astable 
like a
 > > > 555 do the job?
 > > >
 > > > For the high-current, high-speed switch would bipolar transistors
 > > (e.g.. TV
 > > > line-output power devices) or MOSFETS be suitable or would IGBTs be
 > > necessary?
 > > >
 > > > Would it not be necessary to connect a capacitor across the switch to
 > > > absorb/slow down the high-voltage transient produced when the switch
 > > opens/
 > > > would necessary voltage rating of switch and capacitor be comparable to
 > > > that of the primary capacitor in a conventional spark-gap TC?
 > >
 > >Again, exactly what is done in a "conventional" car ignition system.
 > >
 > >Regards,
 > >Malcolm
 >
 >
 >