At 12:34 PM 7/12/99 -0400, Matt Pringle wrote:
>.... what's the difference between an alternator and a generator and why
is the former used nowadays instead of the later?
A generator uses a comutator and brushes to continuously switch the
polarity of the armature windings as the armature rotates, thereby
producing a direct current output. An alternator uses brushes and slip
rings for a constant connection to the armature windings, thereby producing
an anternating current output (thus the name "alternator") which is then
run through a rectifier or a diode bridge to convert the AC to DC output to
satisfy the vehicle electrical system.
Alternators are somewhat more efficient at producing output current from
the mechanical input, so they can be smaller for a given application. For
a given size you can have more power output with an alternator, or for a
given power you can have a smaller size.
Bottom line here is original cost, where the alternator is cheaper in
original manufacture for a given power requirement. However, that doesn't
necessarily make it cheaper to own, just cheaper to buy a new car. The
alternator is likely to require maintainance less often (sometimes never),
but will generally be more expensive to repair than a generator. If you
buy newer cars and don't keep them too long, you might never encounter a
repair bill for the alternator.
If you keep cars a long time and drive them lots of miles, then the long
term maintainance cost of the alternator may well exceed the original
production cost savings. And where you may likely be able to repair a
generator on your own for minimal cost of small parts, an alternator is
more likely to require a more expensive professilnal rebuild at a dedicated
manufactuering plant. Newer alternators are generally non-servicable,
meaning they have to be sent in for a rebuild, but some of the older units
may have replacable brushes and rectifiers.
My MGA is still sporting a generator after 40 years and about 300,000
miles, partly for reason of originality, partly because I can usually
repair it on the fly if required, but mostly because I'm cheap (so tight I
squeak when I walk). Parts to repair a generator will fit in the palm of
your hand, and repair can usually be done anywhere in under a half hour
with a few common hand tools. The same may apply to certain early model
alternators, but usually not for newer units. I see this as making the car
more reliable because I'm less likely to get stranded on the road.
Good used generators and rebuildable cores are cheap and plentiful at swap
meets. I might consider switching to an alternator if the good supply of
cheap genarators should dry up, but I don't see that happening any time in
the forseeable future.
Also generators usually have a low power output, commonly in the low 20-amp
range, while alternators generally put out more power, where 40 to 70 amp
models are common and the sky is the limit. Wanting to install a high
power stereo radio in your car is a good reason for converting to an
alternator.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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