# What is the standard power supply and voltage supply on modern airliners?

I'm looking at reducing the weight footprint of some of the computer systems on a commercial liner. A big consumer of weight seems to be in power supplies and conversion. Being a computer guy, I don't know anything about avionics or electricity on commercial liners.

Is there a standard power supply or voltage supply for modern air liners?

• There are very specialized standards for airborne power supplies, and electronics in general, with specs such as DO-160, DO-178, 400 Hz/AC wild systems, HIRF and lightning resistance, FAA TSO, etc. You're going to have to be a specialist power supply designer to make something that will be allowed to fly. There's no way to take something intended for consumer or commercial use and install it in an aircraft. Jul 9, 2018 at 23:22

Typically 115 VAC, 400 Hz for most large aircraft, which can be rectified and stepped down for DC powered subsystems. Smaller GA airplanes typically use 12, 14 or 28 VDC for their electrical systems.

• Since we are dealing with a computer system, and consistency is important, Is there any standard on how dirty the current can be? Example: They say 28 VDC, but that can drop at any time to 12 VDC for about 30 seconds. Jul 9, 2018 at 23:28
• @RustyWeber usually the voltage won't drop, the frequency will. "Dirty" power is power that has harmonics or noise in the lines, not voltage drops. A voltage drop like that would be a serious problem, frequency is usually OK with +/- some percentage, in grid systems (like in your home) 58-62hz would be OK, outside of that is cause for alarm at the power plant. Jul 9, 2018 at 23:35
• @RonBeyer Not on anything designed A380 and onwards (A350, 787, C-Series). All new designs use variable frequency AC. AC frequency will swing between 380 to 800 Hz depending on engine speed. Jul 10, 2018 at 3:55
• We also see 115 VAC 60 Hz. The 787 has 230(235) VAC variable frequency from the engine driven generators Jul 10, 2018 at 14:23
• They’re not generating electricity at 115 VAC 60 Hz, that’s being created from 400 Hz AC current through a solid state rectifier. Low frequency AC generators are too heavy for use in aircraft. Jul 10, 2018 at 14:45

As far is power sourcing goes, transport jets tend to be AC dominant, with most power generated by a/c generators on the engines, and because some of the equipment is frequency sensitive, the main AC generators use a constant speed drive to produce fixed frequency 115vac/400hz as the primary power source. A minority of the power will be DC, produced by Transformer Rectifier Units that produce 28 volts DC from the AC bus. Most large jet engines are started by air turbine starters powered by bleed air, so on jets the batteries are only used for backup power for basic DC services and to start the Auxiliary Power Unit, which normally supplies bleed for engine starting. If the APU is inop, a jet will need a ground bleed source, or a bleed source from another aircraft using a buddy connection.

Turboprops (and perhaps some smaller jets) tend to be the other way around with a 28 VDC dominant power system, with DC generation from the engines using double-duty starter/generators, and the battery is the starting power source. The engine may also have a variable frequency 115 VAC generator for running non-frequency sensitive components like anti-icing heaters where the higher voltage AC is more efficient. For frequency sensitive avionics, fixed frequency 115/400 hz power comes from static inverters that convert some of the DC power.

Because of the dependence on electric power for main engine starting, turboprops have to have much larger batteries than similar sized jets. And of course watt for watt the DC airplane will have a little bit heavier wiring.