As has been said, some of the earlier aircraft had 12V DC systems but soon 24V DC became the norm – twice the voltage = half the current (Amps) for heavy loads such as engine starter motors. Engine driven generators had outputs of 28V to provide a charging voltage for the battery.
Other voltages are also present, typically 26V AC and 115V AC which were used for systems like remote compass (where a DC supply would have a magnetic effect) and gyro instruments where induction motors could be useful (no brush gear). These AC voltages were provided by ‘inverters’ that changed the DC supply to AC either for busbar distribution or for dedicated system use.
Nowadays (just for interest) all engine driven generators on larger aircraft are 115/200V AC devices of either fixed (pay attention Pagen, I will be asking questions later) or ‘wild’ frequency. The fixed frequency is 400Hz, the ‘wild’ frequency depends on engine speed. 24/28VDC is still used on smaller types.
Yes, electrical systems are my forte in life. Black art, and all that. Just great when no body knows what you are doing. And the airframes are only there to carry the electrics – who said that? :dev2:
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