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
abit 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



Could something like this be incorporated into the flex plate?  Tracy's PSRU
seems to have a lot of open area to route wiring out to the electronics.

Joe Berki
Limo EZ

Certainly could fit in that area. Ideal for use with a carb.

Paul Lamar


Hi Paul,
I took your advice and purchased an old 13b for tear down and
familiarization purposes.  I also purchased Tracy's book and
read it cover to cover 4 times (I learn a little more each time
I read it).

I want to start off sort of in Tracy's footsteps by using carbs.
I have two Johnson / Evinrude 2 barrel carbs that I will
fabricate onto an intake manifold, but I keep getting hung up on
the ignition side.  I think the idea of using an outboard
ignition system is the way to go for me.  I have electrical
schematics for my 1973 Johnson that I can scan and send if it
would help with this thread.  The main components would be
stator, spark advance mechanism, power pack, flywheel with
embedded magnets and coils.

My only question is that on the Johnson, spark advance is
controlled by the spark advance mechanism via a direct
connection to the throttle.  Would we need to incorporate this
into the design for a/c use or is there a different way of
overcoming the spark advance problem?


Franklin

How much HP did the Johnson carbs develop?
To work it should be around 200 to 250 HP.

In other words what is the carb throat inside diameter?
You will need about 3 square inches per carb.
Do you plan to p-port?
http://www.rotaryeng.net/fund-of-intake.html
P-ports are worth it as the intake manifold becomes
trivial to fabricate.

Do you have access to a lathe?
You will need it to make a rotating magnet holder for the
front of the e-shaft. I have a fellow that can make
that part for you if necessary.

Yes by all means scan the Johnson electrical schematics.
That will help when buying parts for the ignition.

Don't worry about ignition advance. Just run the engine
at 22 BTDC fixed. Aircraft engines like boat engines
cruise at one RPM.

Paul Lamar