Commercial aircraft voltage?

Question

What voltage do commercial airplanes work on internally?

I've heard "28V" but with batteries that can mean two different things. For instance a "12V" car battery is 14V practically with the alternator running, the relevant thing is that it's 6 lead-acid cells.

What do airplanes use precisely?

Is there movement toward higher voltages to reduce wire thickness/cost/weight?

Answer 1

28/24 volts, however you choose to look at it. basically, double a car. the reason is mostly because airliners need lots of power. and they have tried lighter, cheaper aluminum wire, but it's too brittle for the amount of vibration it's subject to

Answer 2

28 volts nominal, 24 volts regulated.  Most commercial and military aircraft have used 24 volt systems since early in WWII and many smaller private aircraft are also 24v. The reason, as you surmised, is to reduce the thickness/weight/cost of the wire.

Answer 3

The batteries are 24VDC, the rectifiers running off the 115VAC 400Hz put out 28VDC, which also charges the batteries.

ADDED:

I didn't see any posts in here that said AC was made out of DC, John B. The AC is rectified to DC by the Transformer/Rectifiers (the other T/Rs) to supply the 28VDC to most of the radio and nav equipment. Very little of that equipment is run off of AC except for cooling fans and instrument excitation. This 28VDC also charges the aircraft batteries thru reverse current relays.

And thanks for the thumbs down, I love it!

Answer 4

no airliners produced in the last ten years run primarily on 28v or any dc power. other than a few peices of equipment, radios for instance, everything is ac powered. and no they don't make ac out of dc. engine driven alternators produce the ac which is fed to converters to produce constant frequency ac and what little dc is needed. even emergency sources, e inverters and wind turbines, produce ac. batteries are primarily used to start the apu and some emergency roles such as emergency cabin lighting, that's about it.

Answer 5

Most aircraft have 28VDC, 26VAC and 115VAC 400Hz. The DC voltage is supplied by Transformer / Rectifiers receiving 115VAC from the Generators that are powered by Constant Speed Drives off the Accessory Gear box on the engine. These voltages aren't going to change anytime soon...wire thickness is more a function of current. Then, of course, all the components would have to be redesigned for this voltage change, screws up logistics, etc.

Answer 6

Some commercial aircraft run off two types of voltages.  One is a 28 volts d.c.(vdc).  Which is to say the batteries are 28 volts.  Most of the components use 24 vdc.  Many also use 115 volts a.c.(vac)  This is not the same 115 that comes out of your house.  Aircraft are usually around 400 Hertz(Hz) while the wall outlets in North America are about 60Hz.  There are also some other differences.  To be precise aircraft a.c. power is 115vac 3 phase 4 Wye.  Some lighter aircraft such as Cessna 177 do run off a 12vdc.  

To answer the next part of your question, there is no movement to use higher voltages.  That would also mean increase wire thickness to some components.  Also most aviation components are standardized to run off either 28vdc or 115vac.  So, higher voltages just wouldn't be practical.  

Hope that sheds some light on your questions.