You say the Nova II unit has a fixed timing of 18 degrees (and does not drift with the speed of the motor)?
Isn't that EXACTLY what you are looking for?
Do you have a schematic of the Nova II?
I'm surprised you are trying to figure the capacitive reactance....as the frequencies involved are way too
low to consider that. Simple R-C timing delay is all you need worry about.
Also, in the last issue of the Antique Outboarder, there is my initial writeup on how magnetos work.
However, the ATOM is NOT anything like a set of points! Real points completely short out all voltage
when they are closed (creating maximum current in the primary of the spark coil). The power darlington in
the ATOM modules, in contrast, has about 2 to 2.5 volts of drop across it when "closed"......
Whether you are using points or an ATOM unit, when the "points" open up, the current in the primary of
the coil is interrupted, causing an "inductive kick" (which you see as a spike of 30 to 50 volts). In most magnetos,
you'll see a 100 to 200 volt spike (damped down by the condenser.....otherwise, the voltage would jump to several thousand
volts, causing arcing across the points, and the points would quickly "burn" as a result. That's what your condenser
is for in traditional Magneto setups.)
Those power darlingtons waste a LOT of energy........but if they didn't (that is, if they really shorted out
the voltage completely like points do when they are closed)....there wouldn't be any voltage to turn the power
darlington OFF when you want to "open the points up". This 2 to 2.5 volt drop across the power darlington wastes
a lot of power, lowering the energy that can be converted into spark. You don't get anywhere near the spark
as you do with points, and you need to pull at higher RPM for spark to start with the ATOM, compared to actual
Anyhow.......OldFogeyUK.....what is your goal? It sounds like the NOVA II units give you fixed timing, isn't that
what you want? Or, is the goal to design a ATOM replacement from scratch, that has exactly some specific characteristics
that you need. What is your goal here?