The third brush provides the electrical power to the field coils. The electrical circuit goes from the F terminal, through the field coils, the third brush (insulated), the armature commutator and windings, and then though the grounding brush to the generator case. The circuit for the A terminal is through the insulated brush (opposite the grounding brush) though the armature commutator and windings, and then though the grounding brush to the generator case.
With the F terminal disconnected on the generator and the engine running you should have somewhere from about 1/2 volt up to 3 or 4 volts depending on engine speed. The voltage on the A terminal will be a bit more than that. If you short the F terminal to the generator case the voltage at the A terminal should rise and close the cutout relay in the regulator at which time the voltage will be limited to battery voltage.
DO NOT SHORT THE F TERMINAL TO THE CASE UNLESS THE A TERMINAL IS CONNECTED TO THE REGULATOR AND BATTERY.
If you short the F terminal without the A terminal being somehow connected to a battery the voltage can go high enough to arc through the insulation and ruin the armature.
This post was edited by Owen Aaland at 19:24:44 06/02/14.
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Today's Featured Article - The Nuts and Bolts of Fasteners - Part 2 - by Curtis Von Fange. In our previous article we discussed capscrews, bolts, and nuts along with their relative hardness and thread sizes. In this segment we will finish up on our fasteners and then work with ways to keep them from loosening up in the field. Capscrews, bolts and nuts are not the only means of holding two parts together. When dealing with thinner metals like sheet tin, a long bolt and
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