Alternator Light [SOLVED]

RaceMouse · Post by **RaceMouse** » 21 Nov 2004, 21:19

Greetings,
The alternator light has just begun to tease me. When starting out this morning, the light did not extinguish at low revs as is used to. 360 Km later (motorway/city) we came back home and it was still the same. I measured the voltage across the battery and it was just below 12 volts at idle. As was the voltage between the alternator output and gnd. The voltage between the small wire on the alternator and gnd was ca 4.5 AC. (The multimeter isn't fast enough to show it in DC). What _SHOULD_ the voltage on the small wire be ?
BTW: The wind shield wiper was quite slow on the way home, so I suspect that the battery charging current was at a minimal. I'v read elsewhere on the forum that the diodes could be faulty. Where would they be situated ?
Cheers
RaceMouse

AndersDK · Post by **AndersDK** » 21 Nov 2004, 21:30

Dont think it's the diodes.
Most likely problem is worn out alternator brushes. These are part of the charge module screwed on to the alternator. It's possible to do the brushes alone at very low cost, but fiddly.
Easy/fast solution is a new charge module, not that expensive.
The small alternator wire (charge lamp) should carry either battery voltage or some lowish (close to earth) voltage, indicating either charging or non-charging alternator. You can not deduce any indication from this voltage - other than charging/non charging situation.

wrinklet1 · Post by **wrinklet1** » 21 Nov 2004, 21:46

Hi,
Do a check on your fuse box before checking the brushes, dont forget the alternator needs an electric supply to make it work, without it, it will not work and also shows a light on the dashboard.
Paul

tomsheppard · Post by **tomsheppard** » 21 Nov 2004, 22:48

The multimeter isn't fast enough to show it in DC?
I am sure that you are mistaken.
Dimly glowing alternator lights usually end in one of two ways. Flat battteries or replacement alternators. The latter is the sensible option.

RaceMouse · Post by **RaceMouse** » 21 Nov 2004, 23:37

Hi All,
Thanks for the very fast replies. Ill have a closer look at the alternator brushes tomorrow (it's too dark and cold now

. I'll post the progress.
Cheers
RaceMouse

RaceMouse · Post by **RaceMouse** » 09 Dec 2004, 01:32

Hi again,
After wiggeling about for an hour or so I decided to change the alternator. After a couple of days driving again with full power restored on the battery, I was about to sell the car again : The battery was flat again !
After getting the car jump started @ work, I fiddled at bit with the generator cables while the engine was running. I realized that suddenly the revs dived a little and for a very short time. Hmmmm.... After 2 secs of more cable fiddling I stood with the disconnected cable in hand. I was apparently so corroded that the engine vibrations made the electrical connection really bad. I fixed the corroded cable (still a bit corroded but this time also connected

) and the generator is now charging happily again. If I only knew that from the beginning I would be a 350 EUR richer man. I guess thats called experience...
The conclusion : Checking not only the things mentioned above but also pull the applicable cables could solve the problem without the bigger expences. Especially for theese older cars such as mine ('96).
Once again: Thanks for the help guys

/RaceMouse

dnsey · Post by **dnsey** » 09 Dec 2004, 03:36

I'm pleased that you solved your problem, but would caution against removing alternator leads when the engine is running. Under some circumstances this can damage the rectifier diodes and possibly the regulator in the aternator.

RaceMouse · Post by **RaceMouse** » 09 Dec 2004, 17:28

True, but the wire was alreay loose