Quoting Removed, click Modern View to seeDecreasing current & voltage: Many ballast resistors (including the original 12250 on N tractors) increase resistance as they heat up.
How to measure amperes when running? A current probe on an oscilloscope. It looks like this (lower trace):[URL=http://s192.photobucket.com/user/JMOR_photo/media/Ign/full_cycle_withcurrent_sml.jpg.html][/URL]
Is my tractor operating at 2.82A when running? No, it will be somewhat higher at 'peak', because the average current is lower due to both the exponential rise (see scope current trace) and the fact that points are closed only for the dwell percentage of the cycle. Since the average current is lower, the ballast resistor will cool down relative to steady ON situation, thereby dropping less voltage and giving you a somewhat higher than 4v coil input & thus higher than 2.82A peak.
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