In a message dated 98-06-29 18:23:12 EDT, sweisman@gis.net writes:
> The difference is that an alternator puts out AC
> and a generator puts out DC.
Sumner,
Actually, that's not true. Both an alternator and a generator produce an AC
voltage internally, but both rectify the AC current into a pulsing DC, so the
output is virtually the same in either case. The generator uses slip rings to
do the rectification, while an alternator uses diodes. An alternator has three
stator windings, so the input to the diodes is three phase, while the
generator has a multi-phase winding. The ouput of a generator, then, will be a
little smoother than the output of an alternator, but in both cases they are
still pulsed DC. In other words, the output of an alternator will have three
voltage peaks per rotation, and a generator will have many, smaller, peaks.
The differences between an alternator and a generator are in the details, not
in the concept. Both produce electricity in exactly the same manner, moving a
winding through a magnetic field. The major difference, other than the use of
diodes rather than slip rings for rectification, is in the rotating component.
In a generator, the field winding is stationary, while the output windings
rotate. The external connections to the output windings is through the
rectification slip rings, which limits the amount of current that can be
supplied before arcing at the rings becomes excessive, causing rapid wear and
the need for frequent replacement.
The alternator, on the other hand, lets the field winding rotate, while the
output windings are stationary. This allows a solid, hard wired, connection to
the output windings, eliminating the current limitations of the slip rings.
Diodes can be sized as needed to handle the current. The field winding draws a
low current, so arcing is not a limiting factor there.
For a brief description of how the internals of an alternator work, go to:
http://www.vtr.org/maintain/alternator-overview.html
Sometime, I will revise that article to cover generators as well.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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