Automobile ancillary power

Automobile accessory power can be transferred by several different means. However, it is always ultimately derived from the automobile's internal combustion engine, battery, or other "prime mover" source of energy. The advent of high-powered batteries in hybrid and all-electrical vehicles is shifting the balance of technologies even further in the direction of electrically powered accessories.

An engine has one or more devices for converting energy it produces into a usable form, electricity connection through the alternator, hydraulic connections from a pump or engine system, compressed air, and engine vacuum; or the engine may be directly tapped through a mechanical connection. Modern vehicles run most accessories on electrical power. Typically, only 2% of a vehicle's total power output has gone towards powering accessories. Electrical and hybrid vehicles may use a larger proportion of energy for accessories, due to reduced inefficiencies in the drive train, especially the elimination of engine idling.

Some automobile accessories are connected directly to the engine through gears or belts. These usually require large amounts of power. The air conditioning compressor has been a familiar example, though new all-electric refrigerant compressors are starting to be used in production vehicles.

Early automobiles used a magneto for ignition, which provided no accessory power.

The first electrical accessory connection was supplied by a DC generator. Voltage varied with engine speed and because of technological limitations, complicated mechanical devices were used to regulate it. Even so, voltage at idle was too low to be useful. A lead-acid battery was used to provide proper voltage when the generator could not, and was recharged at higher engine speed or lower electrical load. The automobile self starter was an early engine system to use this.

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