Less than 1/4 amp through a charge light supplied to the excite terminal will excite the alternator, problem is if a charge light or resistor is not used, the alternator will full "field" where the rotor will draw 3+ amps from the 12V source. If using a diode inline which drops voltage a bit, the field current will still be above 2 amps. Only with a charge light or other resistor will the excite current be whatever the light or resistor flows. (usually about 1/4 amp)
I see it every time I put a repaired SI series alternator on my test stand which has a field current meter. An alternator being supplied 12V to the #1 excite terminal will draw 2-3 amps through the field rotor and regulator. Only when the alternator starts charging so the field current can be supplied by the diode trio, will the excite current draw on the #1 regulator terminal go to 0.
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Today's Featured Article - Field Modifications (Sins of the Farmer) - by Staff. Picture a new Chevrolet driving down the street without it's grill, right fender and trunk lid. Imagine a crude hole made in the hood to accommodate a new taller air cleaner, the fender wells cut away to make way for larger tires, and half of a sliding glass door used to replace the windshield. Top that off with an old set of '36 Ford headlight shells bolted to the hood. Pretty unlikely for a car... but for a tractor, this is pretty normal. It seems that more often than not they a
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