If you want the simplest and probably the most reliable ignition system get
a two cycle two cylinder small outboard ignition system.

Fires the same number of times and 180 degrees apart just like a 2 rotor.

As close as you will come to a A/C magneto.

http://www.iboats.com/

http://www.iboats.com/Johnson-Stators/dm/view_id.271367

http://www.cdielectronics.com/
Down load the complete catalog.

Some of these stators are as low as $20 used.

The high voltage coils supply 300 volts for a simple CD system
and the other coils may supply enough 12 volt current for an EFI
system.  No belts.  If the main electrical system or alternator
fails the engine still runs.

This stuff is mass produced in the millions and extremely reliable.

Paul Lamar

Some interesting stuff in that catalog. Some of us wouldn't know exactly
what would comprise a complete system, as it looks like they are all parts
of an upgrade for certain motors.
Did you notice the EFI and ECU units in the catalog? They also note that
these can be reprogrammed for "racing purposes".
Would this be suitable for our purposes? Of course I don't think it would be
a good idea to mention aircraft. One could say I'm making a marine rotary
conversion.
C. Smith


Good idea Craig. A racing rotary boat motor :)

All you need is a source of 300 volts, provided by the rotating magnet
and stationary coil,  a 1 ufd 300 volt cap and a switch of
some sort. An FET works fine and they are easy to use. Way back about 30
years ago we discovered that a 50 cent CMOS CD4050 or a CD4049 chip makes a
great FET driver if most of the six gates in the chip are connected in
parallel.

Since that times 1000's of FET gate drivers have been  designed
and built selling for as much as $6 each and so far I have not
found one that works better than a CD4050.  Many of them require
a regulated supply which lowers efficiency and cost more money
and parts.


I set up this simple CD circuit on the bench in half an hour with a 300
volt DC power supply and it works great.  The FET is a IRF740.

I am rapidly discovering it is all about the 300 volt power supply. You need
a robust power supply that does not crap out when it is shorted to ground
and that is where the charging coil in the outboard motor comes into play.

Nothing could be simpler than a large magnet passing a coil to rapidly
charge the 1 mfd cap.

Paul Lamar
--
So now I have more questions. Does one of these 2 cyl systems have enough
juice to fire both plugs at the same time?
Can it be used for multi-spark, or would one need to stack 2 or more with a
bit of angular offset, then utilize your FET controller to switch the spark?
Last, maybe a failsafe contactor to switch out multispark in the event of a
malfunction of computer to revert to stone axe mode? Or am I making it
overly complicated?
C. Smith


I think stacking two would be needed. The charging coils are available stand
alone and very cheap. All we need do is find the curved magnets stand alone.
Jeff can make the rotating magnet holder. The electronics are trivial
as I just demonstrated.  Here is a picture of what the spark looks
like. The picture is a bit out of focus but you can see the spark.


Paul Lamar

K&J Magnetics makes custom magnets, $150 minimum order. I wouldn't have
a clue as to the dimensions or polarization, but
I'll bet you do. Looks like a quote is free.
http://www.kjmagnetics.com/custom.asp

C. Smith


One of my hangar neighbors fixes Mercury's. I can get the dims
of one of those flywheels. Probably not for a week as I have
to go to PA on biz next week.

Paul Lamar

Check out the last five magnets at the bottom of this page.
http://www.kjmagnetics.com/products.asp?cat=168
A the very least, it demonstrates it is doable.
C. Smith

Looks too small. We need something 3 inch radius
or larger. Some of these big ones are high bucks.

Paul Lamar

Every Day Practical Electronics mag just published
another article by my favorite world wide ignition
engineer. Namely Australian John Clarke.
www.epemag.com The subject was "Replacement Module for
small petrol motors". Page 12

Here are a couple of pictures of a used outboard motor flywheel
I bought for $10 in an outboard engine repair shop. I wanted
the magnets out of it.

Also some more or less self explanatory Figures from the mag article.

Paul Lamar