Darn it! Now you made me study!

(kidding  :^)

I was curious after reading your post as I had never really thought
about the in/outs of an automotive alternator.

An excerpt from http://www.familycar.com/Classroom/charging.htm :

"...... Amperage or current is regulated by the state of charge of the
battery. When the battery is weak, the electromotive force (voltage)
is not strong enough to hold back the current from the alternator
trying to recharge the battery. As the battery reaches a state of full
charge, the electromotive force becomes strong enough to oppose the
current flow from the alternator, the amperage output from the
alternator will drop to close to zero, while the voltage will remain
at 13.5 to 14.5. When more electrical power is used, the electromotive
force will reduce and alternator amperage will increase. It is
extremely important that when alternator efficiency is checked, both
voltage and amperage outputs are checked. Each alternator has a rated
amperage output depending on the electrical requirements of the
vehicle."

For me, it made it clear that the state of the battery determines (in
part) how much current is used. It doesn't explain (in laymens terms)
if the current output is dependent on the RPM of the alternator. i.e.
Does a 70 amp alternator put out 70 amps at idle?

The good news for me is that I'm pretty sure the 90 am alternator I
have on my VanaJetta is not going to somehow be too powerful for my
Westy. Something I was thinking about recently.

Neil.

On Wed, Nov 12, 2008 at 7:15 PM, Richard A Jones <jones@colorado.edu> wrote:
> I'm trying to understand alternators now.  I'm retired,
> so have nothing better to do....
>
> There are lots of web pages that explain how/why the
> voltage is adjusted with the alternator.  What I cannot
> find is an explanation of amperage.  Amps is what charges
> the battery--at the correct voltage.  I do not understand
> how the amperage output of the alternator is varied.
>
> It seems to me that a discharged battery would need lots
> of amps.  A full battery, car with no lights on, etc,
> would need very little.  What does the voltage have to
> do with this, except to correct for the temp of the battery?
>
> You can see how I was a math major, not an engineer.  Help
> me out.
>
> Thanks,
> Richard
>
> To unsubscribe from the Vanagon List send an e-mail to listserv@gerry.vanagon.com with SIGNOFF VANAGON in the body of the message.
>

--
Neil Nicholson '81 JettaWesty "Jaco
http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines
http://web.mac.com/tubaneil
http://tubaneil.googlepages.com/

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