SockPuppet wrote:
In article cc1Xi.198$Cb.81@trnddc08, anonymityisavirtue@
1111011010011.com says...
Alternators have to be supplied with a sufficient current from the
battery in order to generate the larger currents required by the
aircraft systems.

This is a new concept to me, can you elaborate?

My understanding of alternators is that mechanical energy from the
engine causes the alternator to spin, which then powers aircraft
components and (when regulated correctly) can recharge the battery.

First, recall that electricity induces magnetic fields and magnetic
fields induce electricity and vice versa, and vis a vis and so forth.

A simple generator is a wire coil rotating in opposite poles of two
permanent magnets. The magnetic field is provided by the magnet, and the
faster the coil spins, the more often the magnetic field cuts through
the coil (or more properly, the coil cuts through the magnet's field),
the more current is generated.

Alternators use a different method to generate current. There is a
wire-wound stator, within which spins a drum coil (with soft iron
cores). The drum coil (or rotor) has to be energized from an outside
source in order to generate the magnetic fields, necessary to induce
current in the stator windings. While the process is self-sustaining
once begun, alternators cannot "bootstrap" themselves into current
generation (since you can't generate the current to generate the fields
to generate the current, so to speak). Much like the magnetos need the
impulse coupling to push the engine over with a hot spark, the
alternator needs the external "kick in the pants" to begin outputting
current, which is the battery.

Now, as I recall, we use alternators instead because they're lighter,
more efficient, and higher output than can be achieved with a
bog-standard generator.

TheSmokingGnu