Re: My findings on 555 Ign. Coil spark maker thingys

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> Or use a better power transistor with more gain than the 3055 (which has a
> beta of 10-15... not too wonderful, because you probably need 3-4 A to the
> coil, which means it needs 300-400 mA of base drive.)  Given that this is a
> switching kind of circuit, one of the TIPxxx  darlingtons might work better.
> The power dissipated in the transistor is fairly low.  You'll also avoid
> killing the 3055, which is only rated for 60V Vce

	I've had very good luck using an 800 V IXYS IGBT.  Dual 555 drive. 
First one sets the repetition rate and triggers a second which sets the
pulse width.  Drive the IGBT gate through a grounded-emitter buffer
stage and have had no trouble losing any of the components.  The IGBT
runs cool with a coil input current of 10 amps peak at 12 V.  Built the
setup into a neat box, with battery and coil leads on the back.

	I've had much better luck getting long sparks using a QUADRAC driver,
using inductive charging of the energy storage capacitor.  Basic supply
voltage is about 300 from a voltage doubler working off the AC line, and
the inductive charging gives almost 600 volts across the capacitor at
the time the QUADRAC fires.  The coil I have been using is two GMHEI
transformers from the junk yard, primaries in parallel opposing and
secondaries in series, with the low ends connect to the line through
200V MOV's to prevent problems when drawing sparks to ground from either
HV terminal.  The coils are mounted in a polyethylene refrigerator
container filled with mineral oil.  By changing the size of the
capacitor can run the input to the level where the coils will arc over
even under the oil.  5" sparks are easy and steady using a 3 ufd 600
volt capacitor.  Get better results than using the routine light dimmer
circuit, and it doesn't draw high current spikes directly from the line
the way the dimmer circuit does. 

	If anyone is interested I can pass along the schematic and a few more
details.

Ed