Posted by Owen Aaland on December 02, 2011 at 12:02:33 from (216.47.33.145):
In Reply to: Farmall 12 Volt issue posted by rusty wheel on December 01, 2011 at 18:47:12:
Quoting Removed, click Modern View to see
The resistor on the No 1 terminal is used to prevent full charging amperage from coming through that wire if there was a failure of the main battery connection to the alternator. The No 1 terminal has charging voltage applied to it internally through the diode trio in the alternator. If there is a break in the wire connecting the battery to the alternator the total output of the alternator will be available at the No 1 terminal. With no resistor, light bulb, or diode in the circuit the 14/16 gauge wire and possibly the ignition switch could be overloaded and damaged. The excess currant through the diode trio can also ruin it. Incidentally, IH used a 25 ohm resistor on tractors with an ammeter gauge.
Excess voltage applied the the No 1 terminal should not cause the alternator to increase the charging voltage. Charging voltage is controlled by varying the resistance to ground of the rotor field coil. At any voltage above the maximum charging voltage of the regulator will cause the field circuit to open and stop all current flow. Residual magnetism in the rotor can still allow a minimum amount of charge but it will be very little. A field coil shorted to ground may cause the alternator to charge with no control by the regulator but would be rare. I have never seen that happen. Generally failures of the field coil are open circuits, not shorts to ground.
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