Editing Auxiliary power unit (section)

{{Short description|Alternative vehicle power source}}
[[File:AlliedSignal (Honeywell) GTCP36-150 APU2.JPG|thumb|250px|A Honeywell GTCP36 APU mounted in the tail of a [[business jet]]]]
[[File:A380 APU P1230093.jpg|thumb|250px|The APU exhaust in the tailcone of an [[Airbus A380]]]]

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]] and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115&nbsp;[[Volt|V]] [[AC voltage]] at 400&nbsp;[[Hertz|Hz]] (rather than 50/60&nbsp;Hz in mains supply), to run the electrical systems of the aircraft; others can produce 28&nbsp;V [[DC voltage]].<ref name="400Hz">{{cite web |url=http://www.aerospaceweb.org/question/electronics/q0219.shtml |title=400 Hz Electrical Systems |work=Ask a Rocket Scientist |publisher=Aerospaceweb.org}}</ref> APUs can provide power through single or [[three-phase]] systems. A '''jet fuel starter''' ('''JFS''') is a similar device to an APU but directly linked to the main engine and started by an onboard compressed air bottle.<ref>A Jet Fuel Starter and Expendable Turbojet, ASME Digital Collection, by C Rodgers · 1986</ref>