Alternator?

Hi everyone,
I have read a few posts about the symptoms of dying/dead alternators.
I am wondering if what my 98 SL has indicates also a dead alternator.
The instrument panel lights started to flicker at idle two days ago.
The intensity does not just go down but also up. At higher RPMs they
are ok. The dome light, aftermarket radio face, and headlights do not
flicker, as far as I can tell. I did have to replace the battery about
a month ago. Could this be the alternator/slipping belt or just a
deffective light dimmer switch?
Thanks.

 

the lights dim and brighten with the engine rpm? As far as the belt. Nah,
you have a serpentine belt they usally dont slip. and if they do you notice
other things as well.. (ie: power steering jercky, temps higher then normal,
etc)

you mentioned you have an aftermarket stereo installed.. Anything else, like
an ampflier? if you do, your Altenator may not be pushing out enough power
at low RPM. if that is the case you need to get a bigger Alt. Bottom line.
if you see this happening run your car to the garage and have the Charging
system checked..

they will check the alt voltage and amperage.. Could also be something as
simple as corroded battery cables.

 

Check the light in the dark (all interior lights out) while the
engine is being reved. If it lights dimly then the alternator is
going south. If not, it could be going south or not -- hard to say.

 

Dan and Charles,
A good test for an alternator that does not involve the dash light
is to load the system. Do so by turning on the high beams, A/C,
rear window defogger, radio and ... then see if you have more
or less than 12 volts at the battery when you rev the motor to
about 2000 rpm. You should have at least 12 volts or power is
coming out of the battery. Expect 13 or so volts for a successful
test. As the an alternator get more and more miles, the brushes
wear and do not contact the comutator (spelling ?) as well.

chuck s.

 

thats a good test for voltage but you also have to see if the amperage is up
to spec.. you can push 13.5 volt s which is good. but if the ampers is too
low you wont charge at a rate to keep the battery supplied.

 

Another typical problem is that one phase goes out -- either an open
coil or a bad diode. In that case the alternator will still charge
(though not well) but the alternator light will glow dimly (since
it's discharging 1/3 or the time). But your load test will work for
that too, provided that a mechanical voltmeter is used that won't be
fooled by the fluctuating voltage.

 

If the alternator can maintain 13+ volts at full load (and with a
good battery that takes a charge OK) then the amps are good. You
can always take it to a shop where they put it on a load cell and
measure peak amps, but the voltage at full load approach is every
bit as valid.

 

Joe,
Just like what Dan here wrote, with the load being all of the
accessories like the the headlights and rear defroster, a bat-
tery voltage > 12V can not be maintained unless the alternator
is delivering the current. There was a subsequent post from
Dan that also mentions other alternator problems of a bad
diode or bad coil.

I maintain that the > 12V voltage test will spot many of those
as well. As crude as a test as I may have described, it is possible
to do a just a simple meter. And one does not have to remove
the alternator! Like a weightlifter, he (or she) can not perform
a lift with an injury.

chuck

ps: Yes, the tester that many auto stores have is more "precise",
but you have to remove it to test there.

 

Just like what Dan here wrote, with the load being all of the

Exactly........

You should switch your signs though.......should be < 12 volts (for less than
12 volts).

 

Just like what Dan here wrote, with the load being all of the

Whups........disregard my previous post about the signs.......I read it wrong
the first time.......