Alternator vs. Generator

[Speedtree]

The system voltage should always be higher than the battery so the alternator can charge the battery. If the voltages were equal the two would fight and the potential would be for the battery to share some of the load and subsequently be run down. A 24v battery will be with a 28v system and a 12v battery will be with a 14v system.

Another point. Some larger airplanes. I am basically familiar with mine, a conquest, have starter generators and we convert to AC for a few select avionics. We run a turbine engine so the rpm is pretty constant at 41,000 rpm, reduced probably to some lower rpm for the generators. The varying rpm problem is not a factor.

I would guess that even the newer King Airs and other turbo props have something similar.

 

[A Squared]

Sigh..so much mis-information, so little bandwidth.


>>>>generator...creates DC electricity by turning an armature (coil of wire) inside permanent magnets.

No, the magnetic fields are created in field coils, not by permanent magnets. It is true that there are permanent magnet generators, but they don't produce much power, and they are impossible to regulate (except by varying RPM) You may find small permanent magnet generators on an airplane in instrumentation or control circuits (like a tachometer generator), but you won't find them supplying the power for the aircraft electrical systems.


>>>>>Alternators...creates AC electricity by turning an armature (coil of wire) inside a "field coil" which is another wire that has a "trickle charge" of electricity provided by the battery.

No, an alternator creates electricity by tuning the field coils inside the stator, the current is induced in the stationary stator windings...... just like I stated in my previous post.


>>>>>If the battery circuit is removed from the field coil an alternator will not operate (i.e. battery that will hold a charge is essential)

No, once the field windings have been excited, the alternator is producing electricity and becomes self sustaining. You may in fact remove the battery from the airplane once the alternator is producing power and it will continue to do so. The alternator only needs an outside source of voltage initially. There are alternators which need no outside voltage to start producing electricity. They are called "self exciting" alternators. I don’t know whether they are used in any aircraft applications.


regards

 

[V-1]

For Clearsky,

In simplest terms, voltage is a measure of pressure. High pressure always seeks a low pressure. If the battery and alternator/generator were both of the same voltage (pressure), then electricity wouldn't flow properly between them.

Think of two water reservoirs, seperated by a dam. If the water level on both sides of the dam were the same, no water would be exchanged between the two reservoirs (barring temperature differences). If one reservoir was filled to the top of the dam, and the second nearly empty what would happen when the sluice gates were opened?

To move electricity, there needs to be sufficient pressure (voltage) to overcome resistance at the other end (and inefficiencies in the conducting material, of course).

Hope this helps.