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Re: JD model 40 burning points
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Posted by John T Electrical Engineer on August 27, 1999 at 07:46:22 from (63.20.110.43):
In Reply to: JD model 40 burning points posted by Hillory on August 25, 1999 at 21:14:05:
Hillory, I believe all the good ole boys below are right on the money and I like zane's idea best so far. Premature point burn up is due either to a faulty or improper sized condensor or excess current possibly caused by a faulty or improper sized or miswired ballast resistor (assuming you have right coil). You need to insure that the ballast is wired such that the voltage on its low coil side is only about half the battery voltage when running but near battery voltage ONLY when the tractor starting motor is engaged. The design was to jump by pass the ballast only when starting but during normal running it is in series between the ignition switch and coil to halve the voltage and limit the point current. Normally, those ballast are about one half to one ohm and their design was to reduce the voltage to about six across the ballast and the remaining six left across the coil. If the ballast is wired properly and does indeed halve the voltage when running but allow full voltage only when cranking, then you could also have a too low resistance coil (not proper sized for the original JD system) which draws too much point current premature burning them. So, be sure ballast wired right and does as I said, but if problem persists, I would insure you have a good condensor, and if it is, I tend to suspect it isnt the right coil for the system which is too low resistance drawing too much current which will burn points even if ballast an condensor are okay. Farmers often grab a coil laying around when one goes bad and that (if its resistance is too low) can be your problem in addition to bad condensor or incorrect ballast system. The condensor (in shunt with points) charges up when points are open and discharges when closed and its job is to absorb some of the reverse emf arc current which happens when the coil collapses when points open. If not there or not working, that excessive arcing across points premature burns them. Let us all know. John T Engineer in Indiana
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