Paul,

Is using a DC charged cap, dumped to a coil the most efficient way to
generate your big multispark?

You _know_ that a high voltage DC power supply has a fair amount of
circuitry in it to make the output smooth and ripple free.  This
circuitry serves no purpose in your system.  And may likely cause you
operating problems.

What could work really well is a 12V DC driven buck-boost converter,
switched by an oscillator that's running at the frequency of your
spark strike rate.  The oscillator would be gated off when you don't
want any spark.  The output of this circuit would directly drive the
coils.

I haven't run the numbers to see if the AC output from a boost
converter could be made fast enough properly drive the coils.  Might
have to play with a SPICE model to see how it would work with real,
available components.



Matt-

Sounds good. Right now I am using an off the shelf,
300 volt, 30 watt power supply that cost $130. I has a lot
of built in safety stuff. For example if it senses a short
it shuts down. It is also regulated to 9 volts which is
required for starting. My current over all design will work down
to 9 volts or lower using two 14 pin dip isolated switching supplies
that put out 15 volts with only 5 volts in. These are used for
driving the FET's. They too have some built in safety features
that prevent low voltage damage to the FET's.

---------------------------------------------------------
Silicon Chip magazine from Australia is one of the greatest
do it yourself electronics magazine in the world IMHO.

That is where the idea came from for the multi-strike
CD ignition in the first place.

Everybody doing this kind of stuff needs a subscription.
They have an archive of articles going back at least ten years.

http://www.siliconchip.com.au

JayCar, which looks like a UK company, but appears
to be Australian sells kits based on Silicon Chip
construction articles.

http://www.jaycarelectronics.co.uk/

For example here is a low cost switching 300 volt regulated
40 watt supply that could be used for a multi strike CD ignition.
It was intended to drive florescent lamps from 12 volts
but could be used for a CD ignition. It was designed
by the same guy that did the MSD CD ignition. Namely John Clarke
who possess priceless creativity. I don't have the text
for the article but the jpgs are pretty much self explanatory.
If you build one I can help by answering questions. The FETS
and control chip used are outmoded but better ones can be substituted.
It uses one of my favorite old chips (the CMOS CD4050) to drive the FETs.
New control chips have these drivers built in.
The key and priceless info here is how to build the transformer.

Unless you want to learn how to program in ASM Cap Discharge is the
only way to go for stand alone ignition systems. It has to do
with the required dwell time for inductive ignitions.

However I just had a bright idea about that which I will discuss soon
after I test the multi-strike which should be any day now after
I get the final parts.

Paul Lamar


Hi all;
I have a recommendation:  run the  ??Vdc to 300V inverter
flat out until the capacitor voltage reaches about 300V,
and then turn it OFF.  That is, turn off the oscillator or
whatever drives the voltage step-up process.  The energy
will be stored on the capacitor until it's needed.  After
the ignition pulse discharges the capacitor, turn the
inverter back ON and let it run until the voltage once
again reaches 300V.  Don't try to regulate the output
voltage to hold 300V.  You can't do it, really, and trying
to will be expensive and unnecessary.

Most commercial REGULATED DC supplies are regulated to
maintain a precise voltage on the output and DO NOT like to
have the voltage jerked up or down regularly.  It might
cause damage to the supply, depending.


Craig Taylor

I considered that.
Not that easy to do as it requires a high side switch.
Also it takes awhile to turn it on which then requires
a computer to calculate an advance time. Same problem
as the dwell time in an inductive system.

Charged caps can be discharged instantly at the required
ignition time.

This circuit does not jerk the 300 V supply around.
The upper FET turns off the output of the 300 volt supply
about 10 usec before the lower FET discharges the cap through
the coil. It then turns it back on to recharge the cap.


I might do that with the 5 to 12 volt power supply
that feeds the upper FET gate drive. The chip
maker claims it turns on in 2 usec. I am working on
that as we speak.

I will say what acts like that is a charging coil
in an outboard motor CD ignition system. The coil
charges the cap and then a trigger fires the cap
at just the right time. The coil does not get
recharged until the big magnet comes around
again.

IMHO the more I think about it the more the outboard
system seems right for a rotary aircraft engine.

JayCar has a kit for that type of CD ignition
that cost 6.5 UK pounds.

http://www.jaycarelectronics.co.uk/

You still need cap charging coils but they cost
only $40 from the outboard parts suppliers.
The whole thing can be built on/into the flywheel.
Mistral started to do something like that
awhile back. No battery or alternator required
if you are using a carb.

Multiple charging coils spaced ten degrees apart would
do the multi-strike trick.

Paul Lamar