From: worley@a.cs.okstate.edu (WORLEY LAWRENCE JA)
Subject: Re: Am I going deaf?
Organization: Oklahoma State University
Date: Sat, 9 Jan 93 07:22:48 GMT

From article <1993Jan8.062354.10412@lds.loral.com>, by kurnik@lds.loral.com (Timothy J. Kurnik):
> Am I going deaf or does anyone else have this problem?  I find that every 3 or 4
> days, I have to turn my car stereo up another notch to make it sound as loud as I
> like to listen.  My girlfriend says I'm just accustomed to the volume and that anyone
> else who listens to it thinks it's just as loud today as it was a month ago.
> 
> I've check the battery voltage (and it's been load tested by the dealer) and the
> battery seems to be healthy.  Do I need a new or bigger alternator?
> 
> I have a Mazda Miata with an Alpine 8215 driving a PPI 1050 and a PPI 1075 amps.  The                        ^^^^^^^^^^^
                               A WHAT ???
                               Perhaps you mean a 7915 ?
                             

> 1050 (100W) runs the mids and highs in the passenger compartment (2 MBQuart 6",
> 4 MBQuart tweeters and 4 Alpine 3 1/2").  The 1075 is bridged mono (300W mono) to at
> one time a Boston Acoustics Pro 12" in the trunk.  But I blew that one and went to
> the less expensive Volcano Pro 12".
> 
> Some I've questioned have said that I'm not pulling enough amps to warrant a bigger
> alternator. 

Well, it depends... Audio amps place a varying load on the electrical system
of the car their in.  If you listen to it at full volume for long periods of
time, and you have a lot of bass playing (working your 1075 hard), then 
certainly you can pull more amperes than the alternator can deliver.  However,
you are only pulling a *lot* of current when the bass hits hard, as you may
have noticed your lights dim when your car is at idle and the headlights are
on.  If this doesn't occur, then you have no power shortage on the 12VDC side.
If it does (which I'm sure it does), then you are pushing the electrical 
system to the limit, and may want to consider a bigger alternator.

A quick fact about factory vs. aftermarket alternators.  Factory alternators
are usually rated "cold".  That is they will claim "80 amps" of charging 
current, but they don't tell you that's at 80 degrees F.  After the car's
been running for 2 hours, and the core temp of the alternator is 220 degrees,
then the current output can fall *way* down, perhaps to only 20-30 amps!
An aftermarket alternator will tell you both ratings, and you can be
sure that the *hot* rating will not be 20-30 amps!  If you got an 
alternator that could provide 90-110 amps continuously, hot or cold, then
you would have *plenty* of current to drive your existing amps.


> Others have said that I could get a bigger alternator even if I wanted
> one.  They claim that many of the newer cars have computer chips which, among other
> things, expect the output of the alternator to be within a certain range.  If this
> is altered, it could damage the computer.
 
This is a myth, and I will explain it in detail to anyone that wants to 
argue with me about it.  If you're not an alternator designer, then I
suggest you don't.  

One way to look at it is like this:  Let's say you have a jug of water.  Ok,
now let's assume you're REALLY thirsty.  You drink the entire jug of water in
one gulp.  Now, lets say that you get a huge jug.  You are still VERY thirsty,
so you drink the water from this huge jug, and it takes awhile for you to
finish it.  Now, you are standing in front of an ocean.  Are you going to
be able to drink the entire ocean, even though you are really thirsty?  I
think not.  This analogy applies in the following manner.  Think of your
car battery and alternator as a single "current" source.  Together, they
provide the electrical system with 100% of it's current needs.  Now, if
the system needs more current than the two combined can provide, then the
voltage drops, and the system is heavily overloaded.  Now, lets say you
have an infinite current source (1,000,000,000 amp alternator and battery).
Does the radio, headlights, fan motor, computer, dome-light blow to 
smitherines? No.  Why?  Because it only takes as much as it *NEEDS*.  So,
any bozo that tells you that you're going to blow something up by increasing
the current output of your alternator is full of it.  Now, if the alternator
also increases the VOLTAGE output, then you can cause some problems, but
most aftermarket alternators have  an external adjustable voltage regulator,
and your local installer can adjust it properly.

As far as a "computer" in the car monitoring the current output of the
alternator to make sure it's in a certain range, I don't think so.  First of
all, the computer would have to take into account that when the car is 
first started, the alternator generates a TREMENDOUS amount of current for
several seconds/minutes to top off the battery.  This charge rate 
quickly drops to normal after the alternator warms up and/or the battery
is fully charged.

Bottom line (I do this for a living, last 5 years, so you can trust me),
you cannot hurt anything by upgrading your alternator, as LONG as it doesn't
charge at a higher voltage than your stock alternator, it can put out as
much current as you can afford. :)

> is altered, it could damage the computer.  The dealer has no clue on this matter.
> 
> Help...
> 
> SEE YA!
> 
> - T.J.
Newsgroups: rec.audio.car