Installed 120 amp Audi Alternator

[kentmclean at mindspring.com (Kent McLean)]

daniel savatteri wrote:
> Your not affraid of any dash lights or anything urning up?  I would 
> really like to put anther alt with a little more current in my car, I 
> think it would start nicer in ther cold.

A bigger alternator means more current is available to
charge the battery. It doesn't mean more voltage to
your light bulbs.

If you'd like to know a bit more about how your electrical
system works, read on.

First, electricity can be compared to water in a pipe.
Voltage is like water pressure in the pipe.
Amperage is current, or like water flow rate.
See <http://www.boatsafe.com/nauticalknowhow/electricity.htm>
for more details.

To oversimplify the problem, I'll use a toilet as an
example. If your toilet has a slow leak, it uses water
from the tank, but the water supply feed from the wall
is enough to supply the tank with what it needs.  When
you flush the toilet, it empties the tank and it takes
a few minutes for the wall supply to fill the tank.

Now, think of the toilet tank as your car's battery
and the water feed from the wall as your alternator.
Usually, your ignition system and radio usage are
handled by the battery, which is kept charged by
the alternator. (Think the slow leak in the toilet,
which is handled slowly by the tank, which is fed
slowly by the wall feed.)

Say you have a huge drain on the system (like the tank
emptying when you flush the toilet). It could be when
you crank the starter for 10 minutes trying to start
the car in the winter, or a 1000W amplifier driving
your stereo system. To make up for the huge demand,
the battery gives up it's reserve (like the toilet
tank emptying to fill the bowl).

Once the car is started, the alternator recharges
the battery for the next big request. If you are
running the stereo, the alternator can't keep up
with the drain and you will kill your battery.
(That's why some big stereo setups use a separate
battery; the 1st battery will still start the car
and get you home.)

A bigger alternator means that it provides more
current to recharge the battery faster. It still
only puts out a regulated 14V or so. (Think a
bigger pipe from the wall to the toilet tank; it
will fill the tank faster.)

As for burning out those little light bulbs, there
is a voltage regulator so that doesn't happen.
The battery puts out about 13.2 V all by itself.
The alternator, if unregulated, can put out 15 or
more volts. A regulator keeps things in check, so
that the alternator doesn't overpower the battery.
But if the regulator fails, the alternator will
overcharge and kill the battery.  But the rest of
your car will still get just 12V.  (Think of a fire
hose filling up the toilet tank. The tank feeds the
bowl at a constant rate, but the supply line (fire
hose) will overwhelm the tank.)

This isn't a perfect analogy, but it may help
clarify the situation.  Or totally confuse you.

I HTH,
Kent