when we used to test alternators out on tractors and very old cars we used
to hook them up backwards to see if they would spin without bearing noise.

"Scott Gardner" wrote in message
...
On Sat, 17 Jan 2004 13:29:09 -0500, "Mark Zarella"
wrote:

You're absolutely right, Mark. I should have gone back to my
"Electric Circuits" textbook (dug off the shelf after too many years,
obvioiusly) BEFORE I posted my reply. Here's the definition of
"Source" from that book -

"a device that is capable of converting nonelectric energy to electric
energy and vice versa"

So as you posted, a battery satisfies that definition. An alternator
wouldn't, since it only converts one way, from mechanical energy to
electrical energy, not the other way around.

Actually, an alternator is a source too. First, I don't think the "vice
versa" part is necessary, though I can't think of a situation where it
doesn't exist one way and not the other. An alternator, for example, is
a
mere extension of Faraday's law so electrical input would indeed result
in a
force. It's based on the same principles as a speaker or microphone
(which
are essentially the same thing). You can push down on the cone in an
oscillatory manner and a voltage will appear at the terminals, or you can
apply a current and the speaker will move. That means that a
speaker/microphone can also be considered a source, and in fact it's
often
modelled as such.


Yep - it may be an instance of context. In the pastI have used
motor/generators, which obviously do the conversion both ways. The
Naval nuclear reactor I trained on when I was enlisted had several of
them. Since the alternator in a car is never used to convert
electrical energy to mechanical energy, I guess it can't be considered
a "source" - in THAT context.

Scott Gardner