Battery not charging

Hi,

I've been having some trouble with my car's battery for the last week,
and I am completely stumped.
I drive a 1993 240 wagon. It usually runs well, but lately I've been
having trouble with my electrical system. Twice in the last week I've
had my battery die without warning. The battery is less than a year
old, and I had it checked and recharged at the local Autozone. They
told me that the battery is fine, and all the cells are ok. I used a
voltmeter to check the alternator, and it seems to be putting out over
14 volts at the positive terminal when the car is running. I then
suspected perhaps there was a short circuit, so I got an ammeter, and
connected it in series between the negative battery terminal and the
black battery lead. With the car turned off the meter reads zero. I
think this means that there isn't a power drain, but I'm not sure.

One thing that I noticed was that before I recharged the battery the
voltage at the positive terminal was 11.0 with the car running. I got
under the car and checked the terminal connections on the alternator
and they all look like they're securely attached. The green ground
wire was also firmly attached to the chassis. After doing all of this
I still don't know why the battery isn't receiving any charge from the
alternator.

Any help would be much appreciated.
-Randall

 

Okay, you hit the #1 suspect with the grounding wire to the block. My
second suspect would be that the carbon brushes on the voltage regulator
are at their limit. They're attached to the voltage regulator that's
very easy to remove (two screws on the back of the alternator).
Unfortunately the way Volvo wired up the battery light on the 240s the
brushes are part of the circuit, so the idiot light will not come on
when they're worn out (ask me how I know....)

Bill

 

You're right on the way the "idiot light" works, Bill. That wiring
arrangement is common in cars of that era. It seemed like a good idea at the
time I'm sure. The light is between the 12V bus and the excitation terminal
on the alternator. When the alternator isn't working, the current flows from
the bus, through the lamp, through the regulator, through the brushes and
rotor to light the lamp in the process. When the alternator works, it
generates its own voltage to power the voltage regulator et al and the lamp
has no voltage across it. The problem was in that part about the current
flowing through the brushes.... I learned the same way you did, Bill :-(

My experience is that the brushes make better contact when the engine is
cold. The OP can look at his "battery" light when the ignition switch is in
the "run" position and the engine is not running. He can expect to see the
light sometimes on and sometimes off, which strongly suggests the brushes
are worn out (as we would expect in a '93). Or he can replace the brush
block - it's at end-of-life anyway - and very probably solve the problem.

Mike

 

My first thought would be the basics: Check the cable connections for
builtup corrosion and clean as needed. Next check the ground
connection to be sure road salt, etc., hasn't given you a poor ground.

 

Also note well that if the lamp is burned out, the alternator will not
charge. You might get it started with the test lamp, and endlessly
chase your problem somewhere else.

Does the lamp light up when you first turn the key on?

 

I almost forgot about that. Fortunately, it is a relatively rare occurance,
but it can be a puzzler when it happens. Frustrating, too.

Mike