Electronic magneto, magnetron, Tm, operation

[grahampy]

Anybody out there wondered what goes on inside the electronic magneto modules fitted to millions of small engines world wide. I have found that information on the internal circuitry and functioning of these units is either wrong, sketchy or non existent. Usual reply if the engine does not start due to no spark coming
from this unit is, "go buy another one, they are cheap enough". They appear to be the cause of lots of garden equipment ending up in the dumpster. I have tried to examine the internals of these units but de-potting the modules proves difficult. They all seem to rely on a Darlington switching transistor triggered by a tertiary winding on the coil assembly. One Chinese unit that was purchased recently, I managed to partially disassemble, had an obsolete transistor manufactured by a US company that went out of production in the 1990's. I reviewed the thread that featured the modification or replacement of contact breaker ignition circuits with an Atom Module? That unit is a replacement for the mechanical switch part of the ignition circuit and takes the output from the primary winding on the magneto.
Any thoughts on these units, circuit description or details would be appreciated.

 

[alec_t]

Member Debe here is the Atom module expert. Search here for his posts, or threads for 'Atom module'.

 

[debe]

This is the circuit of the Atom Ignition module, used to replace points & condencer. This basic circuit is used internaly in small engine ignition coils. Very hard to dis assemble, but depending on how it failed you may be successful in fiting this circuit external to the coil conected to the kill wire on the coil.

 

[debe]

This is a Briggs & stratton Ignition coil & the circuit which uses a trigering coil.

 

[debe]

This one is of a Ryobi Brush cutter & its a CDI unit built into the coil assembly. Not all that common.

 

[atferrari]

This one is of a Ryobi Brush cutter & its a CDI unit built into the coil assembly. Not all that common.View attachment 123745

Have seen the "kill" expression used with switch and with wire. What function is that?

 

[debe]

Basicly the Kill switch shorts the ignition circuit to ground, to stop the engine.

 

[Nigel Goodwin]

As kids back in the 60's riding, and building, old motorbikes in the fields and on the moors we commonly came across these alternator driven type ignition systems (with points) - and they were a serious 'pain in the bum'. Our solution was simple,we disconnected it, and ran a wire out from the points to a 6V ignition coil we fitted, and a 6V battery - using a simple toggle switch as on/off.

This provided a FAR more reliable ignition system, and much easier starting - and we simply charged the battery off the mains every couple of weeks.

Not so easy though on pointless ones.

 

[shortbus=]

As kids back in the 60's riding, and building, old motorbikes in the fields and on the moors we commonly came across these alternator driven type ignition systems (with points)

That's the thing though, no modern motor even has a place to put or install points.

 

[lloydsteve0]

Anybody out there wondered what goes on inside the electronic magneto modules fitted to millions of small engines world wide. I have found that information on the internal circuitry and functioning of these units is either wrong, sketchy or non existent. Usual reply if the engine does not start due to no spark coming
from this unit is, "go buy another one, they are cheap enough". They appear to be the cause of lots of garden equipment ending up in the dumpster. I have tried to examine the internals of these units but de-potting the modules proves difficult. They all seem to rely on a Darlington switching transistor triggered by a tertiary winding on the coil assembly. One Chinese unit that was purchased recently, I managed to partially disassemble, had an obsolete transistor manufactured by a US company that went out of production in the 1990's. I reviewed the thread that featured the modification or replacement of contact breaker ignition circuits with an Atom Module? That unit is a replacement for the mechanical switch part of the ignition circuit and takes the output from the primary winding on the magneto.
Any thoughts on these units, circuit description or details would be appreciated.

I'll give it go. The Darlington pair has 2 base-emitter junctions in series so base voltage needs to be about 1.5v to start collector current flow and may be up around 2v to enable full load collector current. Collector voltage will higher than that. So when the magneto begins to generate voltage, R1 will drive the base and the transistor begins to turn on and primary current flows from the coil through the transistor. There will be about 2v across this arrangement. Meanwhile the small transistor with only 1 base emitter junction requires only about 0.6v to begin to turn on. The 1.5kohm resistor and 0.47uF capacitor causes a delay in base voltage rising to this voltage. BUT when it does, the transistor begins to turn on and shunts current away from the Darlington transistor base. This causes the Darlington to begin turning off and the voltage across it rises, giving more base drive to the small transistor and the process rapidly continues shutting off the primary current almost completely, and Voila, Spark

That delay caused by the resistor-capacitor (time constant) arrangement can be changed to select the appropriate ignition timing.