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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Today's Featured Article - Talk of the Town: The Saga of Grandpa's Tractor - by The following saga is from the Tractor Talk Discussion Forum. Someone. The saga starts with the following message: Hey guys I have a decision to make. I know what you all will probably suggest and it will probably agree with me way down inside, but here it is. I have a picture blown up and framed in my "tractor room" of a Farmall M. It was my Grandpa's tractor, of which whom I never got to meet. He froze to death getting this tractor out of the barn to pull a truck out of the ditch before I was born. Anyway my dad and aunt had to sell it at the auction,
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