If the capacitor in the alternator is bad it can cause a sensitive digital voltmeter to give widely varying readings. The regulator is either sending full field current through the rotor windings or no current through them. As a result the alternator output is either nothing or maximum voltage. The amount of time the field current is on compared to the time it is off is what determines the average output voltage. The capacitor in the alternator helps to even out the voltage output. Generally the higher the quality of the digital voltmeter the more times per second the voltage is checked and displayed on the screen which results in ever changing numbers. If your meter does not have some capacitance built in when checking voltage the numbers can always be changing. An analog meter simply can not react fast enough to these voltage changes and so the reading is steady. Simply adding a capacitor between the leads of your meter when checking the battery voltage with the alternator charging should make the results readable.
A simple cure for an ammeter that pegs out after converting to an alternator is to run a small wire between the two terminals on the back of the meter. It then becomes a shunted meter and will show amps based on the resistance ratio of the meter and the shunt wire. If you use a wire with the same resistance as the meter the amps shown on the meter will be half of the total amps flowing in the circuit.
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Today's Featured Article - Uncle Cecil's Super A Lives Again - by Mike Purcell. A week or so out of most of my childhood summers was often spent with my Uncle Cecil and Aunt Sissie in the small East Texas town of Maydelle on their 80 acre farm. Some of my fondest memories of these visits are those of learning to drive a tractor at the helm of Uncle Cecil’s 1948 Farmall Super A. Uncle Cecil was the second owner of this wonderful little tractor, but it was almost as though he had adopted an infant. The original owner was a man from Minnesota who bought her from a local dea
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