Radio noise supressors are larger than ignition condensors, as has been widely noted by others. I don't recall a specific value for the noise supressors, but the .47mfd sounds familiar. Delco ignition condensors are in the range of .18-.23 mfd, Ford and Chrysler use larger condensors, but all are based on the inductance of the coil primary winding and the rate of change of the primary voltage when the points open. That rate-of-change is inductance-dependent, with larger inductance causing a slower rise in voltage. I don't remember condensor values for Ford and Chrysler ignition systems, but .23-.25 (Ford/Motorcraft/Ford Autolite) and .25-.28 (Chrysler/Prestolite/Electric Autolite) come to mind. Regarding engine RPM and the points, the faster the distributor turns, the faster the moving contact changes from closed to open as the rubbing block slides toward the apex of the lobe. As that contact moves faster, there is a 'natural' tendency to snuff the arc. (Thats why electrical switches have a 'snap' action- to break the circuit quickly with minimal arcing.) The resonant frequency of the coil primary doesn't change with engine speed or level of magnetic saturation. A frequency change does occur though, when the spark goes out, which causes the coil primary and secondary windings to become one large series-resonant circuit, with a ring frequency considerably lower than the primary winding has during the spark duration. That happens because the 'standard' ignition coil is an autotransformer, with the primary and secondary windings having a common terminal- usually the primary positive terminal. You see this frequency change with an ignition oscilloscope- or any kind of scope that can handle +400 volts input, or a little higher. There are ignition coils that are not autotransformers, but not many in terms of application. Delco HEI coils are one application of that, and there are others.
As far as the noise supressor for voltage regulators, generators and alternators, moving-contact regulators have an arc-supressor resistor that parallels the contact points to supress arcing there, and you don't care especially if the arc is drawn out a little. It is my understanding that the noise supressors in those applications are for dealing with 'ring' frequency of the relay coil that develops when the generator/alternator field current is reduced or interrupted. I think the condensor on the generator armature terminal is more to supress commutator switching noise- watch the commutator on a DC generator with it running at a moderate load- there is continuous sparking at the brushes. For alternators, I think the supression idea is the same as with DC generators, except the output has a fairly large AC ripple component- on the order of several tenths of a volt,depending on the stator winding, condition of the diodes and load on the alternator. And there is no arcing in an alternator output as there is with a generator commutator. The alternator field (rotor)also resonates to some extent when the voltage regulator switches field current to control the alternator voltage.
Enough said- I don't mean to clutter up this whole discussion.
Harvester
