Hello, I would like to make a CDI for a 4hp outboard without battery; I have to pull a cord to crank) . I want to control the advance with a (arduino nano or better a) MSP430 (because of the fast booting time). I made a first simulation but have a lack of data: how much energy/volts can I generate from a Yamaha F4B monocylinder with a one-magnet flywheel at lets say RPM160 cranking RPM). Then I could make the simulation more accurate. All the problems are (for now) in the low RPM's at start where I should have enought energy to start a microcontroller and charge a condensor. My microcontroller should only delay the pulse to the Mosfet or SCR depending on the RPM.
I add a first LTSpice asc attempt...

 

The magneto-generated voltage varies wildly depending on cranking speed and magnet strength. Do you have a means of actually measuring it (preferably a 'scope)?
Couldn't you use a small battery to power the MCU during start-up, and let the magneto take over to provide its power after start-up?

Edit:
Your diodes are wrongly configured in the sim. Full-wave rectification won't work in that circuit if the magneto coil has one terminal permanently grounded.
Your sim supplies the 7805 regulator with 300V. That's way beyond its 35V maximum!

 

The magneto-generated voltage varies wildly depending on cranking speed and magnet strength. Do you have a means of actually measuring it (preferably a 'scope)?
Couldn't you use a small battery to power the MCU during start-up, and let the magneto take over to provide its power after start-up?

Edit:
Your diodes are wrongly configured in the sim. Full-wave rectification won't work in that circuit if the magneto coil has one terminal permanently grounded.
Your sim supplies the 7805 regulator with 300V. That's way beyond its 35V maximum!

You're right about the voltage. This was in fact a first guess... I have a scope but not the 1:100 attenuator to protect my scope (Bitscope). About a single rectification: In fact I tried to circumvent this with an extra diode D5, and double rectif. so that I could pick up more energy from that sensing coil... I guess thats not the correct way to do?.

 

I guess thats not the correct way to do?.

It's not. Check the current through D4 !!

 

current through D4 !!

Indeed. Way to high. I changed to single rectif.
How do the CDI producers arrange the coil and windings so that the core is used as part of the sensing coil but probably also as part of the primary/secondary. I see only one (open ended) iron core... how should I proceed..

 

This project will probably not work because of
the way that 2-Stroke-Outboard-Motors are normally have their RPMs controlled.

You didn't specify the Engine,
this could be a standard Industrial-Engine strapped to the back of a Long-River-Boat.

Standard-Outboard-Motors control low-speed operation mostly by varying the Timing-Advance or Retard.
There is very little change in the Throttle-Position until somewhere around 1/2 to 3/4 of maximum RPMs.

The safe operation of the Engine, ( meaning adequate-oiling of the Bearings and Cylinder ),
comes from a partially open throttle, in combination with, purposefully Retarded-Ignition-Timing.

You are probably aware of the current method of Ignition-Timing-Control on your Engine.
If the Timing is normally mechanically varied along with the Throttle through a linkage,
DO NOT MESS WITH THE TIMING, YOU WILL DESTROY YOUR ENGINE.

If You have an "Industrial-Engine",
research into the Ignition-Systems used by 4-Stroke-Go-Kart-Racers.

This may be an entertaining challenge for You, and I don't want to take that away,
but there is little to zero advantage in Power to be gained from this Project,
and You might destroy your Engine.
.
.
.

 

This project will probably not work because of
the way that 2-Stroke-Outboard-Motors are normally have their RPMs controlled.

You didn't specify the Engine,
this could be a standard Industrial-Engine strapped to the back of a Long-River-Boat.

Standard-Outboard-Motors control low-speed operation mostly by varying the Timing-Advance or Retard.
There is very little change in the Throttle-Position until somewhere around 1/2 to 3/4 of maximum RPMs.

The safe operation of the Engine, ( meaning adequate-oiling of the Bearings and Cylinder ),
comes from a partially open throttle, in combination with, purposefully Retarded-Ignition-Timing.

You are probably aware of the current method of Ignition-Timing-Control on your Engine.
If the Timing is normally mechanically varied along with the Throttle through a linkage,
DO NOT MESS WITH THE TIMING, YOU WILL DESTROY YOUR ENGINE.

If You have an "Industrial-Engine",
research into the Ignition-Systems used by 4-Stroke-Go-Kart-Racers.

This may be an entertaining challenge for You, and I don't want to take that away,
but there is little to zero advantage in Power to be gained from this Project,
and You might destroy your Engine.
.
.
.

Thanks for your advise. It is a 4 stroke F4B monocylinder of Yamaha. I guess it is a wasted spark CDI which normally is on it, but after <20 hours of functioning it stopped (no spark). So the engine (3 years old) is quasi new. I know that at 1500 rmp the advance is 8° and at 3500RPM: 37°. The ignition timing is said to be using a microcontroller (workshop manual). I would simulate functioning out of the engine in order to preserve the engine.
I tried to remove the magnet on the flywheel but the bolts are fixed. I guess with Loctite or so. I do not want to apply heat since I guess it will destroy the magnet. On the other hand I do not want to use a hammering screw driver since I could destroy the bearings of the crank shaft.... so I am somewhat blocked. I only found the CDI at 1/3 of the price of the engine and consider this to be at least unfair.