Posted by MarkB_MI on August 25, 2014 at 02:50:19 from (70.194.9.9):
In Reply to: condensor posted by Leroy on August 24, 2014 at 19:38:24:
I have never heard anyone raise the question as to whether ignition coils are interchangeable, or if ballast resistors are interchangeable. In fact, folks swap those part out all the time when doing a 12 volt conversion. Of course, coil inductance and ballast resistance are fairly consistent across all manufacturers and applications.
Most manufacturers used only a few condensors across all their applications, even though in theory the capacitance value should be tuned to the application for best point life. That should tell you it's not that big of a deal; if the condensor will physically fit it will electrically function.
The old service manuals from Motors, et al. always talked about reading the points to see if the condenser value was too high or low, as if you could pick a different value off the shelf. In practice all you could do was swap out the condensor and hope the new one worked better than the old one. I've never heard of somebody sorting through condensors with a capacitance meter to find the ideal value, but I suppose somebody has done that at some time.
What changing the capacitance does is to change the resonant frequency of the RLC circuit formed by the condensor, coil and ballast resistor. When you open the points, the voltage across the points will "ring" until the points close again or all the energy in the circuit is used up by the resistor. I assume the idea of picking condensor capacitance is to select a frequency where the points will close at the moment the voltage crosses zero. The problem with that theory is that few engines operate at constant speed, and even for those which do it would be very difficult to tune the condensor to match the zero crossing to the engine speed.
This post was edited by MarkB_MI at 04:23:29 08/25/14.
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