Posted by Janicholson on November 03, 2011 at 18:40:31 from (96.24.99.126):
In Reply to: Re: H Charging system posted by glennster on November 03, 2011 at 10:03:14:
Sure. The two types of Delco generator encountered on a Farmall have either three brushes, or two brushes. Both systems use an external ground to allow current to flow through the field windings. Thus there are connections inside that provide the Hot side for that current. The three brush gets its field source from the third brush, picking up voltage from the commutator next to the primary ARM connected brush. The closer it is to the ARM brush, the more voltage is available to be used by the field then out the F terminal to ground (in those it is directly grounded if the 4 way switch is set to H D or B and through a resistor if on L.) To check for internal shorts to ground, the 3rd brush must be isolated from the commutator. Lifting the brush, and putting a plastic knife, or piece of butter tub top, under it accomplishes this well. now, if the field wire is not on the F terminal, the entire field winding set is insulated from ground. If it is found to be not insulated the fault is either the brush holder, or a wire in the windings or attachments touching the frame, or iron cores of the field. Infinite resistance when checked with an ohm meter between the case and the F terminal is a good thing. Near zero to 2 ohms will be measured between the Isolated brush, and the F terminal. If a two brush is tested, the field is attached to the ARM brush directly, thus as it gets volts from charging, it is directly energized. To isolate the field it is also necessary to isolate the ARM brush Thus the Arm brush is lifted and an insulating shim is inserted as above. The Bat post must also be disconnected from the regulator because there are windings in the regulators cutout relay that will be connected, and not to be included in the field circuit analysis. The F terminal is also disconnected as above. Again the result is an isolated field. The Ohms from case to F terminal must be infinite. the ohms from the Arm terminal (this time) to the F terminal should be near Zero or 2 ohms. To isolate the Armature from ground, it is necessary to raise the ground brush (only) and insulate that as above. With all terminals disconnected, the ohms between the Arm terminal and the Case should be infinite. The measurement from the Arm terminal to the Commutator bars under the lifted brush will be Zero or less than .5 ohms. The Armature has heavy windings and little resistance. The isolated brush is grounded and should have zero ohms between it and the case. I hope this is the discussion you asked for! Jim
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