Posted by Owen Aaland on October 02, 2010 at 13:23:43 from (65.174.247.47):
In Reply to: Electrical for Dummies posted by John Lundberg on October 01, 2010 at 16:39:49:
Quoting Removed, click Modern View to see
When alternators were first introduced DelcoRemy referred to them as AC generators.
The electricity generated in the coil windings of both DC generators and alternators is AC current. It is generated by passing a coil through a magnetic field.
In a generator the magnetic field is created by the field coils and pole shoes mounted inside the case. One pole shoe will be a magnetic North and the other a magnetic South. The coils moving through this magnetic are mounted on the armature. The ends of each coil is attached to commutator segments mounted 180 degrees apart. As the coil passes through the magnetic field one end of the coil will have a positive charge and the other end a negative charge. As the armature turns past the magnetic field of the N pole shoe and enters the magnetic field of the S pole shoe the positive and negative charges in the coil will be reversed. This means the electricity generated in the individual coils is indeed AC current. A generator rectifies this current to DC by mounting the brushes so that when the N & P charges in the coils are reversed the commutator segments now contact opposite brushes so the electrical output will always flow in the same direction.
An alternator generates the electricity by rotating the magnetic fields inside the stator coils. The rotor of the alternator has a coil in it that becomes an electrical magnet when current is passed through it. One end of the rotor will be the N pole end and the other will be the S pole end. On each end of the rotor coil is an iron shell that has fingers that intertwine with each other. One of these shells will be the N pole of the magnet and the other will be the S end. Since they are intertwined there is a magnetic field between each gap creating multiple magnetic fields around the outside of the rotor. The electricity is generated in the stator windings that are mounted in the case. Usually there are three windings in automotive alternators. (The stator windings will have their ends connected in pairs [Delta] or share a common connection on one end and individual wires on the other end [Y]). Each end of the stator windings is connected to a pair of diodes, one N and one P. The diodes rectify the AC current to DC output.
The main advantage of an alternator over a generator is that in a generator all the generated current has to pass through the brushes while in an alternator the only current passed through brushes is the field current. Generator bushes contact a segmented commutator and when current output is increased, arcing between the brush and commutator becomes a problem. Brushes in an alternator contact slip rings so they maintain a constant contact resulting in longer life that in a generator.
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