:: Running voltage

[Qube]

Pulled up the OBC on the e39. With just the fresh air on and no lights (NOT STARTED), it says 11.8v. With the lights and radio on it goes to 11.7v. Accelerating or just on gas brings it to 13.4v-13.6v. Off the throttle and cruising is about 12.4v... stopped at the light goes back down to 11.8v (STARTED, of course).

Does that sound right? Seems a bit low.

[whiskychaser]

Pulled up the OBC on the e39. With just the fresh air on and no lights (NOT STARTED), it says 11.8v. With the lights and radio on it goes to 11.7v. Accelerating or just on gas brings it to 13.4v-13.6v. Off the throttle and cruising is about 12.4v... stopped at the light goes back down to 11.8v (STARTED, of course).

Does that sound right? Seems a bit low.
11.8v does seem a little low. The alternator wont kick in until you are on fast idle. You will have to check the spec for your alternator-some are supposed to charge at over 14v. Mine tends to run at 13.6-13.9v according to the OBC but I would use a DMM at the battery for accuracy. Isnt the acid test if you switch everything on and the system voltage doesnt drop when at fast idle?

[ryan roopnarine]

i just had an alternator in the 1999 ford taurus pee the bed. at idle, with headlights on, no problem, but when one put a decent number of accessories on, it wouldn't charge fast enough. right now, with a new battery in it, with a/c, radio, rear defroster, headlights on, and at parked idle, the voltage at the battery is 12.15-12.18. at a decent charging rpm, it is much better. it sounds like you are a fair bit under where you should be. i'm surprised that your radio does not go intermittent or that you don't have intermittent cel/abs lights flashing.

[pingu]

With the engine not running, I get about 11.8V. This is on a new battery.

With the engine running at idle (600 rpm), I get about 13.6V.

When driving, the voltage fluctuates between about 13.6V and 13.9V (occasionally hits 14.2V)

[Ross]

I agree it's low. Start by checking the belt, if tight then the regulator is suspect.