rocktown61201

Hello, I have a 2004 2.7 A6 that has its battery light on. I just took it down to the local auto parts store and they stated it was only @ 12 volts/30 amps with a half charged battery...so it appears the alternator is not charging.

I had the same issue this past spring and had my local auto shop (trusted) that I've used before on the car to preform the switch out. My alternator was replaced with a new Valeo unit.

Has anyone else experienced an issue similar to this where a second alternator was needed very shortly after it was replaced? I wont know more until tomorrow, but I have to imagine that there is a warranty on the unit, but obviously not on the labor it will take to put the car into the service position and back again. Any feedback is appreciated, thanks.

Brad

RMsALFA

Alternators can fail at any time, as can batteries.

It is not unknown for relatively new batteries to crap out. Before going through the much higher expense to change out the alternator, BE 100% SURE it's not the battery. Put it in a different car, or something, and see if it charges to full capacity.

Alternators can be tested in place if you can find someone with the equipment to do it.

SloopJohnB@mac.com

It's fairly surprising that a new/rebuilt alternator failed so quickly although some might argue infant failure syndrome on new electronics, i.e., diode bridge or voltage regulator.

The rest of the alternator is pretty mechanical, bearings, slip rings/brushes, rotor, field coils (unless someone has come up with a permanent magnet setup a-la starter motors) so failures are rare.

Chances are your voltage regulator crapped out this early...there are any number of cheap charging system testers out there (Sun even makes one) that will give an LED-type readout on voltage, AC component (if a diode opens or shorts in the bridge you will get a large AC component or missing phase in the rectified current) or diode failure.

Alternator failures are rare and almost always due to wear of the slip ring brushes or voltage regulator failure, discounting damage to alternators from running without the belly pan and crud getting up in them such as salt, road grime, etc.

Just IMHO...

rocktown61201

I did have both the battery and the alternator tested and the battery was found to be good, the alternator bad. On the way to the shop today I seen the light go out occasionally and the alternator charge up the battery to 14 volts...then the light would come back on and the voltage would drop to around 12 volts. I mentioned this in hopes there is a bad connection somewhere.

Thanks for the replies so far, I'll report back with the findings when i get them.

Brad

4Driver4

New alternator, or rebuilt? If new, it's a fluke or something else is amiss. If rebuilt, who did you buy it from?

SloopJohnB@mac.com

Still sounds to me like a voltage regulator/worn brush issue.
Pull the alternator, remove the voltage regulator and LOOK at the brushes. 5mm is the wear limit.

On some Bosch alternators you may be able to crimp pigtail/solder pigtail onto the VR but on my 4.2 alternator I had to buy a complete new VR.

rocktown61201

Sorry for the slow response, life has been very busy for me lately...thank you to all who have supplied advice.

The alternator I was replacing the factory unit with was the Bosch Valeo, rebuilt. The shop said it was another alternator and it had a warranty so I was only stuck with labor...

However, today I noticed my volt meter starting to slip below 12 volts when parked with the A/C AND lights on. The battery signal beeped at me on the dash info center briefly and then dissapeared. There is no red "battery" light on the dash as there has been previously.

This new incident to me sounds like there could be something electrical causing the alternator's to fail prematurely or it needs a new battery...here are my syptoms:

-While idling with the A/C AND lights on, the volts are approx 11
-While driving with the A/C AND lights on, the volts are almost 12

-While idling with the A/C on, the volts are almost 12
-While driving with the A/C on, the volts are 13

-While idling with the lights on, the volts are almost 12
-While driving with the lights on, the volts are almost 12

FWIW, O'Reily Auto Parts said the alternator is only charging the batter @ 30 volts and it needs replacement. Any suggestions are once again appreciated. The car is not stumbling or having any other issues. Thanks in advance.

Brad

SloopJohnB@mac.com

Do your own load test on the battery. Load testers r cheap. I have three cars and load test the batteries twice a year.
Check electrolyte level on battery.

4Driver4

Bought alternator from a national chain? Bad alternator.
Joe at Axis next time.

Just Me

Yep. Agree. The solid state part or the brushes.

problem is, especially with rebuilt, the brushes can be crap, wrong, installed improperly, sticky, etc.

Rectifiers depend on the quality you buy. Most re builders dont buy high end stuff.

I'll note, i have foudn that there ARE great re builders out there, but you need to find them. And the local parts guys may nto know or ack it. My local NAPA says A-1 cardone calipers are pretty good. They are not. not even close. yet NuGeon are excellent.

Parts are not parts,

G