How much voltage should alternator put out & where to take reading?

[bdv]

Have replaced alternator and new belt. With nothing turned on I am reading 14.50 volts at the battery terminals with my digital meter. My voltage gauge on the dash is reading 14.0 volts (which I don’t put much faith in). What is throwing me is my scan tool (OTC 4000E) is reading voltage as 13.0 volts again with nothing on. If I turn headlights, radio, cooling fan to max, I get 12.5 on scan tool and 14.0 volts on my digital meter at the battery terminals. Should I be taking the reading at the battery, should I take reading elsewhere? What should the voltage be? Why I am getting such different readings between digital meter and scan tool?

Thanks for the help Brent.

[moondoggie]

Good Day!

The primary requirement of a charging system is obviously to keep the vehicle running; a close second is to recharge the battery after cranking the engine. The voltage at which the charging system does this is determined by what

[jspringator]

I appreciate your write up, moondoggie.

[Hubert]

Hope you don't mind me tagging along on this one. Cranked up this afternoon and my dash's voltmeter reads approximately 11.5. (This after dropping transmission and inspecting slave and throwout bearing for naught uhhgg; sorry separate issue.)

The voltmeter is suppose to be around the 14V mark idling right? (I havent' driven it much lately) normally it moves a little down with glows on (W.T.S.) and starting and during afterglow but now it just stays around 11.5 volts. Looks like its creeping down real real slow (watching while driving home with headlights on). The battery idiot light on the other side of the dash did not come on??? (it does come on with key on run engine off with all the other dash lights so its good???) When would that come on to indicate a problem? RPM guage seems to working fine. The Belt is a little old but not bad it doesn't appear; its not sqealing or anything pretty good tension etc.

Does it matter which battery you use the DMM on?
Any other easy diagnostics to be done with a DMM?

I know my leads are clean and batteries spin cranking fast for now. I added a second ground on both batteries a couple months ago. Drivers side to fender. Passenger battery to the ground at the back of the intake near the coolant recovery tank. Just had leads off and cleaned 2 weeks ago.

While putting transmission back in I had to jack the back of it up a little high to get crossmember back in and the transmission mount etc. Could I have pinched something somewhere to kill my alternator? Everything else is fine?

Thanks,
Hue

[johnny2can]

Originally posted by Hubert:
The voltmeter is suppose to be around the 14V mark idling right? ... Looks like its creeping down real real slow (watching while driving home with headlights on). The battery idiot light on the other side of the dash did not come on??? ... When would that come on to indicate a problem?
- 14v, no load, is what I get on both my gasser 'burb and my truck... seems typical

- creeping down? no idiot light? I replaced two alternators last year (1 Volvo, 1 gasser 'burb)... the Volvo has an idiot light but no volt meter (but a manual reading showed similar results), the 'burb acted just like yours. In neither case did the idiot light ever come on.

My theory is that the alternator was puttin' out enough juice to keep the idiot light off, but not enough to power everything and charge the battery. Imagine my surprise (both times, since I learn slow) when the next time I jumped in it didn't start! smile.gif

I'm lazy, so I just bought new alternators both times, instead of replacing the worn brushes.

[dieselrealtor]

My voltage gauge was dropping a couple of weeks ago, slowly from about 14, 13, 12, ...
then, finally the tach died & the idiot light came on, this happened over about 3 weeks time. Just put a autozone gold on & life is good again, volt gauge reads about 13.5, have not checked it at the battery but it seems to keep up with the heavy loads of both ac fans running full blast, etc. :cool: