The generator has a single set of windings used to generate electricity. All of the electrical current made by the generator passes thru the two carbon brushes that ride on the commutator end of the armature.
Because there is only a single set of windings in a generator the output is limited at idle and low rpms, and the overall output is limited by the size of the field coils and the rest of the internal parts. Spinning the generator faster at higher rpms (above factory recommended rpms) will not increase output (will actually reduce output) because the brushes will begin to lift off of the commutator.
The other thing that happens is the generator overheats from excessive voltage, which causes the solder to melt that holds the segments onto the armature. When that happens the segments will come loose... bind up with the field coils and your generator is toast.
In the old days they called this..."throwing the solder out of the generator..." The same can happen when you adjust the regulator to increase output above the factory settings. The generator will overheat the solder will melt and you know the rest. You have caused more harm than good!
It also makes sense that the two biggest wear items on a generator are the brushes and the bearings on either end of the armature. When both are ignored either the brushes will wear down and become short enough that they no longer make good connection with the commutator or the bearing (in some applications bushings) wear out and the armature no longer runs true between the field coils. The armature can then rub on the field coils, damaging both the field coils and the armature. That means you would have to replace both the armature and the field coils...if you can find them!
Finally...new or rebuilt generators often suffer from improper installation. Mechanically, the installation is straightforward but electrically, things are a little more complicated. When the generator is removed from the vehicle for service there is residual magnetism stored in the pole field coils. The polarity of the generator is determined by the direction the current was traveling in the field coils when it was removed from the vehicle. If... during rebuilding and testing process the current is caused to flow in the opposite direction, (improper testing procedure) the pole shoes will change polarity.
If the generator is then installed on the vehicle, (and the generator not polarized) the reversed polarity will cause the electrical current from the generator to flow in the wrong direction, damaging the regulator (you would be sending positive ground current to your negative ground regulator) and discharging the battery when the car is left overnight. Therefore, all generators must be polarized after installation, and before running the car.
As we discussed earlier...generators produce direct current which is what all automotive electrical systems run on, even today. By contrast alternators produce alternating current and that current is converted to direct current. It has to do with efficiency... read on!
Alternators have the big advantage of producing a greater amount of current at low speeds as compared to a generator. In an alternator, the "field" windings are placed around the spinning central shaft rather than on "shoes" as in the generator. Two iron pole pieces, cast with "fingers" cover the field windings, and the fingers are interfaced. The fingers on one pole piece form the North poles and the fingers on the other form the South poles. This assembly is called the ROTOR.
Surrounding the rotor are a series of windings around laminated iron rings, attached to the alternator's case. This assembly is called the STATOR. The engine's crankshaft spins the rotor inside of the stator.
Direct current from the battery is fed through into the rotor's field coil by using brushes rubbing what are called slip-rings. One end of the field coil is fastened to the insulated brush, while the other end is attached to the grounded brush. As the pole fields pass through the stator, current is electromagnetically produced (just like in a generator) but since the rotor is composed of alternating North and South poles the current produced flows in opposite direction every 180-degrees of rotation. In other words, the current is "alternating."
Why is this more efficient? Because the stator windings are made up of three separate windings. This produces what is known as three-phase alternating current. When only one winding is used, single-phase current results (like in a generator). In effect, the alternator produces three times the current of a generator for the same effort on the engine's part. Also, alternators are considerably lighter and smaller than generators and can produce a greater amount of electrical current to cover increased electrical loads.
Converting Alternating Current To Direct Current
This is done by passing the alternating current thru silicon diodes. Diodes have the ability to allow current to flow readily in one direction only, stopping the flow if the direction reverses. Multiple diodes are arranged in alternators so that current will flow from the alternator to the battery (in one direction only, creating direct current) Diodes are a solid-state device which means they have no moving parts.