auxiliary battery charging

An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft, naval ships and some large land vehicles. Aircraft APUs generally produce 115 V AC at 400 Hz (rather than the 50 or 60 Hz common in mains supplies), to run the electrical systems of the aircraft; others can produce 28 V DC. APUs can provide power through single- or three-phase systems. A jet fuel starter (JFS) is a device similar to an APU but directly linked to a main engine and started by an onboard compressed air bottle.

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