Alternator dying?

[amagalla]

Hello all,

I've been investigating the source of some alternator whine that I have coming through my stereo. With the car at idle, I checked the voltage at the battery. It's seeing only 13.65 volts. This seems a bit low to me, but I don't know enough about the Porsche alternators to say for sure. So I pose the question: Is my alternator dying?

Thanks

Tony

[Steve Tinker]

No, @ 13.6 v, that's OK for a fully charged battery condition.....

A better (quick) test is to check you battery voltage after the car has sat for an hour or so - a fully charged battery should indicate 12.6v. Now start the car for a few minutes and check the voltage again @ idle which should indicate your 13.6 v. Increase the revs to +/- 2,000rpm and see if the voltage rises to +/- 14.0v to 14.5v, steadily dropping as the battery reaches a fully charged state.

A fully charged battery will show only about 13.5v charge from the alternator but a low charged battery will show over 14v from the alternator.

Alternators will whine when under load and rumble when the bearings are worn.