wrote:

> There's more to it than that. The arc that jumps the points
> as they open represents continued current flow, reducing the sharpness
> of the magnetic flux collapse that generates the spark voltage in the
> secondary. The condenser provides a temporary path for the electron
> flow as the points begin to open, and by the time the capacitor is
> full the points are too far apart to start any arcing, and the current
> stops much more abruptly.

That's an interesting way of putting it.

The coil capacitor combination form a resonant circuit. When the points
open the output is a very high voltage AC waveform if you don't have it
hooked up to a spark plug. With a spark plug in the secondary circuit
there is a discharge before the AC wave form reaches it's first peak.
Before the points open the condenser is not in the current path. A
capacitor will not pass DC current but does pass AC current.

>A bad (open) condenser will kill the engine
> just as quick as a shorted one.
> Just try starting the engine without the condenser installed;
> it won't run. Not enough spark. The automotive textbooks I've read
> have only the "points-burn prevention" theory as the reason for the
> condenser. Not until I studied for my aircraft maintenance engineer's
> ticket did I find the real reason for it in the aircraft texbooks. An
> old guy once told me many years ago that the (auto) engine wouldn't
> run without the condenser; he didn't know why, just that it wouldn't.
> I tried it, and sure enough, dead as a doornail.

That's right the condenser is designed (by design the correct size is
picked to match the coil) to increase the voltage. The increased
voltage actually increases the arcing at the points simply because more
voltage means more arcing. There is another capacitor that is often
placed on the positive terminal of the coil that is designed to reduce
noise.

-jim


> My Unison/Slick magneto manual says that the condenser also
> boosts the mag primary current for the next firing; this is true only
> because the magneto generates alternating current for the primary, as
> opposed to the DC system in the car.
>
> Dan

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