Is 13.5V enough?

Hi all,

My alternator warning light has been glowing (bright enough to see in the daytime) and I just had the voltage checked. It's putting out 13.5V max and about 12.75V at idle. The car is a '71 911E with Webers.

The warning light was on for about two weeks before I could get it checked out, but I haven't noticed any trouble with cold starts or dim headlights (and I've been driving the car frequently and for long durations).

My question is this: At 13.5V, is the discharging just so minimal that it's going to take a long time to notice any symptoms?

I've read through some previous posts on the subject and I've seen that anywhere from 13.5 - 14.5 volts is the normal output. The current output is definitely on the low end, but is it still good enough?

We're going to change the regulator just to see if that fixes the problem, but if not, should I go ahead and replace the alternator to be safe, or can I afford to wait until I start noticing a real drain on the battery?

By the way, this is a great BB. (I'm a recent convert from RennList.)

thanks!

Might be the regulator, or the diodes that make that ac to dc (don't remember the correct...name..rectifier?) Those might make that warning light shine. The voltage seems to be just fine, if it were 12V or only a bit over then the battery would discharge. The diodes are cheap to fix, if you are able to take the alternator apart.

So basically if one of the diodes is busted, it will eventually destroy the battery or something else before that. Older cars dont have so many things that require "straight" DC voltage, newer need the charging device to be in perfect condition (ICs and other devices)

13.5 V max might be on the borderline. If you have a lot of accessories ON (lights, fan, A/C, etc.), the alternator may be operating at a deficit (e.g. battery discharging). A more normal max. charging voltage is around 14.5.

I'd suggest taking your car to an auto. electric shop or two and have the system checked out before you replace too many expensive parts.

Sherwood Lee
http://members.rennlist.org/911pcars