Nope, it's the field


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Posted by David Sherman on Sunday, October 10, 2004 at 9:56PM :

In Reply to: Re: anyone remember how to polarize the generator posted by Tom Petroff on Sunday, October 10, 2004 at 6:51PM :

Momentarily jump the field to the batt terminal. The field is what's wound on the frame of the generator. Its polarity determines what polarity of current the generator generates, and the amount of current going through it (controlled by the regulator) determines how much current comes out of the armature ("ARM") terminal. The field has a relatively high resistance, and jumping it to the ungrounded battery terminal should make only a small spark (just visible).

The armature terminal goes via the brushes to the rotating part of the generator. This is what makes the electricity. It's the opposite of an alternator; in an alternator the "field" is wound on the rotor and is connected via slip-rings. The the windings that make the juice are wound on the non-moving frame, which makes the brushes don't have to carry as much current but the current generated in the armature windings "alternates" as the field spins, producing alternating current that has to get rectified into DC by the diodes inside the alternator so it can charge a battery.

On an old-fashioned generator, jumping the armature to the battery post will make a pretty hefty spark, and if left connected for long is liable to overheat the armature windings or arc and damage the brushes or commutator (slotted copper part that the brushes run on). The good thing is generators and electromechanical regulators are even more forgiving of mistakes than alternators and transistorized regulators, so if you just briefly "flash" the wrong terminal, you probably won't hurt anything. On most generators, the armature terminal is a heavier post than the field one. Most old regulators have "BAT", "ARM", and "FLD" stamped on their terminals.



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