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Pirkka

Well Known Member
I think I understand the basics (read some articles) but what confused me was these positive and negative pulses talked here lately (in context of spark plug rotation). I would understand that we generate only either positive or negative (compare to ground) pulses with magneto but how the change is done? Is it single magneto unit which generates positive or negative pulses or will one generate a bit (half) of both?

Links, pictures or anything to get me understand this is appreciated. Thanks for the answers already!
 
The magnet inside the magneto has a north and south pole, as all magnets do. When rotating in any given direction, the voltage generated in the coil by the north pole passing the coil will be opposite of that generated by the south pole. On a magneto, the resulting high voltage pulses will be opposite the one previous - so the first pulse will be positive with respect to ground, the next will be negative, the next positive, then negative, and so on. Since the magneto is geared to the engine rotation, the same polarity always come out of the magneto at a given firing point in the rotation and gets sent to the plug.

On any engine with an even number of cylinders, a given spark plug will see the same polarity on the voltage all the time. This polarity can, over time, cause metal to migrate from one electrode to the other, or cause more wear to one electrode than the other. Therefore, when changing plugs for cleaning, you want to move a plug that has been seeing positive spark voltage to a location where it will have negative spark voltage, to balance the wear. This is the same idea as rotating tires, you just balance the wear patterns to get the most use from the plugs/tires.
 
Because it is not immediately obvious, there is a menu under the "components" text at the top of this animation that allows you to select the "operation" section. This gives you animations of the actual operation including the impuse coupling.

Very cool tool!
 
I was told not to run an engine that is equipped with electronic ignition and a mag, to not turn off the mag in flight, because it will harm the mag. (because electrons not having a place to go (?) From what I understand the way both systems work it would be better if the mag was turned off (in flight) to recieve the full benefit of the electronic ignition. Is this correct or should I go back to my dual mag?
 
Brian: that really wasn't obvious so thanks for pointing out it!

hudgin: You really know what to ask. I've been wondering same thing for a some time; if we have magneto (consider it ancient system) and electronic ignition (consider it modern one) if magneto ignites before the electronic system what's the benefit having one? Or do we set magneto to ignite later than normally (double magneto system) to make sure it doesn't work before electric ignition has already hit the spark? Or the way you say: let's just turn off magneto while cruising...

Let's hope someone has more wise words!
 
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