OK, I can see that but I'm just not familiar with that type of ignition system nor magneto.

These ignition systems are basically powered by a magnet molded into the flywheel at the right spot. They flywheel is held for correct timing with a woodruff key (shear key, many names) to make sure the position of the magnet is correct to induce a current in the coil mounted next to it at the right time. There isn't a battery to provide separate power to the ignition, or any alternator. Older and very very simple engines do not have points, only the magneto to control timing (along with spark plug gap). You don't really see this setup in anything these days.

The points are added for a better spark. The magnet in the flywheel and coil are similar. They are powered by a smaller coil on the magneto, like a step down transformer. Instead of the spark appearing whenever the magneto has built up just enough voltage to jump the spark plug gap, the points control the spark release more precisely. This allows the spark to occur at the same point in each revolution and with more voltage, taking the actual spark plug gap out of the timing equation.

 

Hi All, this is john 47 years old from the Netherlands.
Been reading this thread with great interest, here is the deal
Got an old 2 cilinder 2-stroke outboard engine a Chrysler 205Hb, was searching for a way to eliminate points and capacitors, and came upon this thread.
The outboard gave no spark at all and after some examination i find out one of the coils was shorted.

Dismantled the the top end of the outboard, ordered some new coils and replaced both coils so to make sure i started fresh.

Made the points conversions like DEBE described in this thread http://forum.allaboutcircuits.com/showthread.php?t=47639&highlight=magneto+module
I must have made some mistake, and i dubble checked everything but i cant get the darn thing to spark.
The engine is set up with a flywheel with a fixed magnet passing the coils at every reveletion of the crankshaft, the more throttle i give the more the ignition base plate is moving towards earlier ignition, if i dont make any sense let me know english is hard to type and especially tecnical english.
I am totally baffled right know in what to do, can someone point me in the right direction ?

 

It all depends on the polarity of the pulse from the Ign coil. Try conecting the module up in reverse polarity. Its a trial & error thing with the polarity of module to coil.

 

It all depends on the polarity of the pulse from the Ign coil. Try conecting the module up in reverse polarity. Its a trial & error thing with the polarity of module to coil.

Did the wire switch, no luck
narrowed the sparkplug gap and woohhoooo there was a spark, did the same thing with the other sparkplug and now i have a great spark on both plugs, thanks !!

 

Its been awhile but hadn't realy given up on this project. Have since found some cheep 2SD1071 transistors to use in this module with higher voltage rating & designed for ign circuits. Also found it needed a Mossorb 1.5KE200 [ 1N6303A ] across the transistor. Fitted the module to an old Victa 2stroke lawnmower & removed the points & condencer. It ran well & did over 1hr work with no problems. Pics of how it was assembled.

 

Couple more pics of finished module.

 

Hi debe, do you have any idea of the primary side voltage on the coil when the engine is running? I have a stalled project, a gasoline powered "pogo stick", is the reason I'm asking. This is basically just a two stroke engine cylinder with a rod that interacts with the ground, strictly a reciprocating linear movement, not a rotation like an engine. The mechanical parts are all worked out, but the ignition needs to be powered by a battery, not a magneto, and don't know the primary voltage on a magneto style coil. Thank you for any information you can give on this.

 

Usualy 6V is plenty to fire a magneto coil. That's what my magneto coil tester uses.

 

Thank you Daryl!! That was my guess, going to try a 6V lantern battery.

 

i would like to make some of these for my old outboards, i can see the pics but would like a step by step if anyone has it? not even sure where to get the parts to make it up but will inquire at radio shack or an electrical supply store. not an electronics gur but ver good with a soldering gun and epoxy. i think i understand for the most part from the pics posted but still reluctant that i can do this.

 

For electronics this is a pretty simple circuit. The pictures are in a step by step sequence of construction. The 2SD1071 transistor was from Ebay, as it was the only place I could find them at a reasonable price.

 

thanks debe, followed to this site from aomci. it is the picture once you have it set in epoxy that was confusing to me. you have a different piece than the pictures showed. that looks like the improved part you mentioned earlier though. I will try this as it seems easy enough to follow. not something I am familiar with but would like to see my 12hp Scott running better and parts difficult to find.. thanks for the info.

 

What happened was I built several, then found I needed to add the extra part. Sorry about the confusion but I cant post pictures on AOMCI, they were posted by someone else so I wasn't able to add an update. Theres pictures & a video of the module on an old 2stroke lawnmower on my photo bucket debe5.

 

what is the extra part added and what is it soldered to? is it another capacitor mounted externally?

 

The added part was a 200v MOSORB 15KE200A (IN6303A) added across C & E of Q1. In the picture its soldered across the black & red wire. It was added to protect the transistor from excessive voltage spikes.

 

thanks debe, I will order the parts and try this on a couple motors and let you know. great information.

 

I have ordered all the parts on eBay and a couple have arrived this week. I am hoping to get the rest before the holidays and will attempt to build during that time. I will post results and pics once done. thanks again debe.