Chainsaw / Strimmer / Mini Moto Engine Ignition

Gallery, Projects and General > How do I??

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MrFluffy:
No points involved at all, the magnet on the flywheel induces the flux directly into the primary windings of the coil, and a separate trigger coil also inside led the trigger coil deals with precise timing. So no external bits. Its all inside the coil itself. They are TINY too.
Here's a link to read up on the briggs system, you can see one fitted to a racing briggs engine in the article, just the coil pack and some magnets on a disc to induce the voltage from. The larger mowers have large flywheels because they need to generate +12v to charge the battery for the lights/starter motor etc but they still rely on just a coil and magnet to do the spark. This being the racer it can be stripped to the barebones needed.
http://www.foxvalleykart.com/timing2.html

Ill try and remember to get a photo of the size of the strimmer engine components, they make the briggs kart stuff look huge. Minimoto are the same, just a magnet and coil pack and all the ignition trigger stuff is encapsulated into the coil.

MrFluffy:
That sounds awfully technical. A more normal summary :-
Bolt the coil onto your engine somewhere you can arrange a magnet which rotates with engine speed to pass a set distance away (its in the spec of the motor). Use the original magnet from the donor engine and mount it so it spins as before. Spin the engine. A spark will happen at the ht lead at the correct time and the insides will deal with spark advance with rpm and everything.

Thats it. No more bits needed. You can get fancy and add a lead to connect the coil terminal to ground via a switch to cut the engine if you want.

NickG:
Pretty impressive, simple idea. Definitely got to look into this when I make my first I.C for a self sufficient , compact ignition system. Thanks for the info.

Nick

John Swift:
Hi MrFluffy ,

I think the transistor circuit replaces the contact breaker I'm thinking of
on the magneto's used on very early agricultural engines

I assume with the coil short circuited by a closed contact ( or electronic switch )
the rotating magnet induces a large current in the coil
producing its own magnetic field

when the switch opens a large back emf is produced as the field collapses
to generate the HT to the plug

John

krv3000:
hi i dont no if this will help but sum pics of a coil and pick up

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