History of Automotive Alternators

The advantage of alternators

Alternators have several advantages over DC (direct-current) generators. Alternators are lighter, cheaper and stronger, and they provide a useful charge while the engine is idling. At the same time, the alternator uses slip rings which greatly extend the life of the upper brushes on the commutator (or a completely brushless design). In addition, the brushes in the alternator only carry DC field current which is only a small part of current carried by the DC generator brushes, while the entire output of the dynamo is carried by the brushes. There are the car alternator, truck alternator, forklift alternator, excavator alternator and so on.

A set of rectifiers (diode bridges) are needed to convert the AC to DC. In order to provide low-ripple direct current, multi-phase windings are used, and the pole pieces of the rotor are shaped (claw poles). Automotive alternators are usually belt-driven at 2–3 times crankshaft speed, a speed that can cause the commutator in the alternator to fly apart. The alternator runs at a different RPM (changing frequency) as it is driven by the engine.

Alternator regulators are also simpler than generator regulators. A generator regulator requires a cutout relay to isolate the output coil (armature) from the battery at low speeds. This isolation is provided by the alternator rectifier diodes.

History of automotive alternators

During World War II

The modern type of vehicle alternator was first used in military applications to power radio equipment on special vehicles. After the war, other vehicles with higher electrical demands, such as ambulances and radio taxis, could also be fitted with optional AC dynamo.

In 1960

Chrysler first introduced an alternator as standard equipment in a production car on the Valiant, years ahead of Ford and General Motors. Some early cars, such as the Ford Model T, used a different charging system: a magneto driven by the engine generated low-voltage alternating current and fed it to the shock coils, which provided the high voltage needed to generate the ignition spark. Since this magneto system relies only on the movement of the motor to generate current, it can even be used to start a hand crank motor, as long as the crank is pulled sharply, the magneto will generate enough current to give the coil a good spark. The Model T incorporated a magneto into the engine flywheel. The first T-models used magnets to ignite only the shock coils.

After 1915

Ford added electric headlights, also powered by magnets. Magnetic circuits are strictly AC circuits, excluding batteries. There was a switch on the ignition coil that could be replaced by a battery, which was helpful for cold-weather starting, but Ford neither offered nor encouraged its use until the introduction of the electric starter in 1919. Owners must install the batteries themselves and charge them externally.