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Discussion in 'General Engine Discussion' started by Bruce R., Feb 1, 2020.
Anyone out there ever tried adapting a weedwhacker magneto assembly to a model engine ?
Bruce--That is a great idea. Sooner or later I am going to design and build another engine, and I think having an "on board" magneto would be a very good idea.---Brian
hello there is a great book on ths subject @ "model-engine-plans.com/books/index.htm" or J.E. Howell model engine plans. hope this helps
hello forgot to mention the name of the book is ignition coils and magnetos in miniture by Bob Shores.
I was also wondering if one of those little permanent magnet generators off a bicycle would make enough juice to light off a coil during the initial starting of a model ? I don’t know what they put out.
Magneto ignition chainsaw type engines have been around RC engines for decades. The engines themselves are sometimes modified from their industrial roots but I think by & large used the same ignition components to deliver spark. The trend is has been towards electronic ignition because a lot of the mag stuff is big & heavy. Whether that could be miniaturized or modified is above my pay grade. I suspect it would require some electrical engineering know how. This link shows some of the mag & conversion kits so you can see both angles.
The Bob Shores book is as dthrow55 mentions - dedicated to designing & making miniature ignition systems from the ground up. I'm actually not too sure about availability. This looks to be a digital version sneak peak?
Two designs for small model Mags in Model Engine Builder magazine one HT by John Vietti and a LT by Don Grimm. Digital back issues still available.
There is also the kit sold by Minimag but that is a bit large and can look out of place on smaller engines
The entire ignition apparatus does not scale down well.
1) the spark energy is the same no matter how small the engine is
2) the insulation and clearance needed do not scale at all.
That said... a Kettering system stores the energy in thy coil and a Magneto depends on similar principles such as flux changes linked to many turns of wire.
In contrast, a CDI ignition stores the energy into a Capacitor.
It turns out that electrical insulator are far better than conductors, therefore a Capacitor can store more Energy/Volume than an inductor, provided one chose a sufficiently high voltage.
The pulse transformer of a CDI does not store energy, is essentially a high frequency transformer and can be made very small because transformers volumes goes down with frequency.
It remains the issue of charging the cap at the typical 200/400V. With modern technology it can be miniaturized using semiconductor and high frequency switching.
I am amazed at the tiny circuitry in the little cubes we all use to charge our cell phones. They can take 220v down to 5v with a tiny transformer and switching circuit. Seems like some potential in these little units for charging a capacitor.
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