The magneto circuit was strictly AC, with no battery included.
Beginning with the 1915 model year, Ford added electric headlights, also powered by the magneto. The first Model Ts used the magneto solely for the trembler coil ignition. The Model T incorporated its magneto into the engine flywheel. (This was different from a true ignition magneto, which generates high voltage directly.) Since such a magneto system only depended on the engine's motion to generate current, it could even be used when starting a manually cranked engine, provided the crank was pulled sharply, so that the magneto would produce enough current for the coils to make good sparks. Some early automobiles, like the Ford Model T, used a different sort of charging system: an engine-driven magneto which generated low-voltage alternating current that was supplied to trembler coils, which provided the high voltage needed to generate ignition sparks. Īlternators were first introduced as standard equipment on a production car by the Chrysler Corporation on the Valiant in 1960, several years ahead of Ford and General Motors. After the war, other vehicles with high electrical demands - such as ambulances and radio taxis - could also be fitted with optional alternators. The modern type of vehicle alternators were first used in military applications during World War II, to power radio equipment on specialist Fitted For Wireless vehicles. At medium speeds efficiency of today's alternators is 70–80%. Efficiency reduces dramatically at high speeds mainly due to fan resistance. Įfficiency of automotive alternators is limited by fan cooling loss, bearing loss, iron loss, copper loss, and the voltage drop in the diode bridges. The windings of a 3-phase alternator may be connected using either the delta or star ( wye) connection regime set-up. Brushless versions of these type alternators are also common in larger machinery, such as highway trucks and earthmoving machinery. Larger vehicles sometimes use a field coil alternator, as used in large machinery. However, a small proportion of cars use a water-cooled alternator instead of an air-cooled design. The smaller, enclosed fans produce less noise, particularly at higher machine speeds. The closer core spacing from the rotor improves magnetic efficiency. The stator windings now consist of a dense central band where the iron core and copper windings are tightly packed, and end bands where the windings are more exposed for better heat transfer. Two fans are used, one at each end, and the airflow is semi-radial, entering axially and leaving radially outwards. In this design, the casing has distinctive radial vent slots at each end and now encloses the fan.
Modern alternators typically use a 'compact' layout which results in better cooling. These alternators have their field and stator windings cooled by axial airflow, produced by an external fan attached to the drive belt pulley. The coil is mounted axially inside this and field current is supplied by slip rings and carbon brushes. The poles of the rotor look like fingers of two hands interlocked with each other. This uses a shaped iron core on the rotor to produce a multi-pole field from a single coil winding. Most passenger vehicles and light trucks use alternators with Lundahl or 'claw-pole' field construction.
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