New alternator last summer, generic.
Now on occasion, after sitting overnight it will show the battery light after startup. Voltage check then will read like 10.5. Not good. But in storage it is holding volts around 12 fine, but immediately drops in this condition.
New Optima yellow battery.
So if, in this state, I hit the gas to get it over idle for like 2 seconds, the voltage immediately climbs to 13.8, something "clicks", the lights get brighter, and it will stay this way as long as I drive it.
So......what's going on here?
some relay not closing all the way?
Bad internal voltage regulator on alt? (but why would a slight, one time increase in RPM fix that?)

Any ideas?

 

Maybe the clutch on the alternator is freezing?

 

I don't think mine has a clutch?? At least not externally

 

Interesting possibility and had to look that up. Doubt the OP's generic alt has a clutch type pulley. Appears OEM alt on mine has a straight pulley as most available replacements I've seen do.

Depending upon "around" battery may not be fully charging or not holding it. If not above 12.5 after sitting a couple of hours or overnight you may want to remove battery, fully charge, load test if possible, top off charge and reinstall. If symptoms go away temporarily charging system would be suspect.

Audible? If so probably just a result of a low voltage issue and not a cause.
......

 

Sorry boys. Used to the charmers I work on. Alternator clutches on alternators are used in our application for energy savings and management.

Thought these pups may have one. Regulator is could be on its way out

 

I bought this new optima battery to rule out the battery. It hasn't solved the problem.
Before I turn the car on, battery has 12.2 volts, then it immediately dumps to 10 upon running in this state, until I touch the gas once

 

Not sure if this helps or not but i had a similar problem like that. Turns out when i did my head gasket job i didn't ground the eng to the chassis properly. Normally the negative goes to the chassis and the eng block but my setup was different at that time because i have a dual battery setup where both grounds are hooked together but one battery grounds to the block and the other grounds to the chassis. i took the one that grounds to the chassis out to replace it and started have similar issues. if it is a grounding issue there is a grounding strap at the rear of the driver side head that after a while falls apart.

 

I tend to lean toward a ground issue. I would check all grounds, engine, body,etc.

 

Mine behaved very similarly recently. Eventually killing the battery. During the alternator replacement, I noticed that the small "brown & red wire" attached to the back of the alternator had apparently broken. I could rev the engine and the battery light would go out. I repaired the wire, put in a new alternator and battery and I've had no problem since.

 

have your charging system check, i think you have a two fold problem.
you need to be charging at 13.5 or better,and you battery should not be dropping to 10 volts unless you have been cranking on it for a while