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Multi cylinder ignition systems

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gbritnell:
I believe S&S supplied a small capacitor for their ignition when using points rather than a Hall sensor.  My Holt has a points trigger but I have never used the capacitor and haven't had any problems.

Roger B:
The voltage rating of a wire is complicated. A piece of typical PVC panel wire will withstand around 20kV short term, 6 kV long term but will carry a rating of 1000V. For long term voltage rating the quality of the conductor surface and the lack of an air gap between the conductor and the insulation is important to control the corona discharge which will cause long term breakdown.

Adding some resistance to the ignition wires or plug caps reduces the rate of voltage rise and the amount of RF interference produced.

Capacitors are used with traditional points and coil ignition systems to reduce arcing at the points, as the points open the capacitor holds the voltage across them to zero until it charges up. By the time the capacitor charges up the points should be open enough to withstand the voltage. The capacitor also allows for some resonant oscillation to prolong the spark.

petertha:
Mike, if I recall your Jupiter distributer correctly, you initially considered both a shutter wheel type & a magnet disc type. You went with a shutter wheel & confirmed it functioned well on a bench rig so ended it there, at least for now. And you have also made a magnet disc type on different project.

Are there pros, cons or limits where one system would be net better performance than the other? My own naïve assumption, at least for a distributer of say 1" diameter or larger & 4-9 cylinders max, is a magnet disc is possibly a tad easier to fabricate. Disc requires N holes for N cylinders equally spaced. Magnets are spit cheap so buying 1 vs buying 7 more for an 8-cylinder doesn't seem like a concern. I've seen neodiums available as small as 1mm dia x 0.5mm thick. Maybe that's too small or maybe the quality / consistency factors in this? The shutter wheel requires a bit more careful milling compared to N spotted holes for a magnet disc, but not a huge difference either way. Maybe crowding too many magnets in too small a space on its disc can create issues? Or spinning an array of magnets in close proximity to the upstairs rotor assembly is less desirable for some reason & requires more vertical offset distance between them?  I think I'm hearing the hall effect sensor is essentially the same if not identical. They are also a relatively inexpensive component & require about the same consideration/methods to mount. I am also considering making 2 types just to see, but wondering out loud why not magnet disc type first?

gbritnell:
The only issue with a magnet disc is there is no way to control the dwell. With a shutter disc you can control the dwell with the size of the windows.

petertha:
Thanks George. I have no idea if my sketch is a figment of my own imagination so hopefully its understandable enough for this purpose, or correct me as needed. I've read some hall effect sensor specs & I understand ~20%. Using your V8 shutter & magnet dimensions as example, are you saying that the aperture width would constrain (reduce) the interval time the sensor sees compared to a bare magnet in a disc something like so?

I assumed the way CDI modules worked is they had some kind of internal logic; when the hall tripped ON based on some minimum magnet strength, they applied their own 'on time' spark duration based on that signal point mainly so it met the requirements of the capacitor discharge. But maybe it will attempt to deliver for as long as as it detects ON & that's where shutter controls? Now maybe I'm getting messed up with similar discussion on the RCEXL type modules that keep track of pulses & time & therefore know RPM & how to electronically apply advance/retard... they are a different animal apparently even though they also use hall sensors. I should probably address these questions to S/S but bottom line is I think their base configuration assumes a magnet disc? But I think I've also read where people use a shutter with S/S.

https://www.cncengines.com/ic.html

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