Bad Battery? Alternator?

[MrSony]

Drivin around, specially that it's gotten colder, my volt gauge will only read about 12ish volts, especially at low idle in gear (5-600rpm), but once i get going again it goes upto 14.5. Lights get brighter too. Any ideas? The battery was in a garage on a shelf from Feb '17 to last November. It's only 2 years old. Cranks good, doesn't slow down at all.

 

[airboatgreg]

Check connections first but I am leaning toward a dirty commutator in the alternator. I don't know what alternator you have but if you full field it for 10 seconds that may clean off the grunge

 

[Jeff L]

Makes me think it is something to do with the alternator because you mentioned how the lights get brighter. I had similar issues a few times where my lights would get brighter, dim, depending on how fast the engine was revving. Alternator was the culprit and a new one solved the issue. If you have a voltage tester check the battery before you start the car. Then check it after you start and if the alternator is working you should see the voltage going up because the battery is being charged like it should. The readings in the 13-14 volt range are normal, I think, if the system has been working ok?

I would check your battery connections and make sure your wires and connections are clean and secure. Bad ground connections can mess things up. If you can have the battery checked you never know with them too. Weird electrical issues can occur when a battery seems ok but it is not.

 

[pontiacgp]

What have you turned on, the rear window defogger and blower fan takes alot of juice. What is the engine's revs at idle?

 

[olds307 and 403]

My reman 12si 94 amp does that same thing, has since day one, acts like a one wire voltage regulator. Does it stay charging once revved up a bit?

 

[Flyers9928]

Check your belts! make sure that its tight and not slipping.

 

[Chris Tomas]

If its not your belts, its the alt, my oldsmobile has been giving me charging problems lately, and one of the replacement alts i tried did exactly what your did, go get it tested for free at partsource cause chances are its shot.

 

[1bad79]

What size pulley is on this alternator? That can have an effect on low speed charging

 

[MrSony]

What have you turned on, the rear window defogger and blower fan takes alot of juice. What is the engine's revs at idle?

No rear defog, and blow motor is toast. No heat. Only thing that runs is my radio and my gauges (3 pd, volts, oil, temp, and tach). All wired correctly. Radio stuff is all stock 33 year old GM. Even the speakers. Sounds like sh*t.

Edit: I have noticed, that when the radio is ON, but turned all the way down, sometimes I hear static.

 

[MrSony]

What size pulley is on this alternator? That can have an effect on low speed charging

2.6" according to my digital calipers, probably closer to 2.5, 2.6 seems like an odd size. Measured on the face of it, don't know if it matters.
I never had a problem with this before. The alternator also sat on a shelf from Feb '17 to last November, but it's a mostly clean single car garage.