car battery/alternator question

[chataigner]

LOML's little Renault has the battery warning light on when driving. Fan belt OK, no slip. I've checked battery voltage, it is normal, that is 12 ish with the engine not running, drops a tad if you put the headlights on etc., but, and this is the bit I dont understand : rises exactly as one would expect to around 14v when the engine is running (revs dependant). That all seems to indicate that everything is working as it should. So why the warning light ?

She only told me about this a couple of days ago, it seems the light has been on for a week or more with the car in daily use (2 or 3 hrs of use par day).

Help !!!

 

[Burnerman]

This is generally an early warning sign that the alternator is about to go AWOL.......they don't always fail this way but it looks like the 'slip rings' and brushes are on their way out. These provide the alternator with its exciter current (input if you like) so the alternator can give its full output.
Expect around 14.4v irrespective of RPM really, once the things spinning.
John

 

[Mursal]

As its a Renault check the earth strap on the Alternator if its got one and the connections from the Red lead on the alternator to the starter. Dirty fuse might also be a culprit, but most likely alternator.
Wiggle the key a bit to see if it goes out? You can quote me if you like, she will really appreciate that one.