Ok, I have a 99 Z28. The car sat for about 6 months after I popped the motor. I pulled the ALT and it tested good, pulled the batt and it tested good. Alternator is showing 14.3 volts open circuit, but I can't find anywhere that can give me a short circuit current.

The car seems to hold charge around 12.3 volts. But that's it. My current theory is that the alt is making the appropriate 14.3 volts, but is not capable of producing enough current. Theories?

 

You might just need to put the battery on a charger for a while. My car was barely driven all winter and the battery was weak in the Spring, and the alternator couldn't get it back to where it should be. Took the battery out, put it on a float charger for a few days, put it back in and it's back to normal. The alternator is really just designed to maintain a battery that is already charged.

 

what are you talking about when you say open circuit voltage on the alternator at 14.3 volts?
and to say you can't find anywhere to give you a short circuit current... is correct because if you did that you'd blow the alternator or melt wires.

with the engine running at idle, no lights/radio/heater on if you put a volt meter on the battery on the + and - terminals, you should see over 13.5 volts. fyi this is measuring the voltage on the circuit in parallel. if you turn on the lights/radio/fan you will notice the idle dip briefly as the alternator now has a decent load placed on it, but your voltage at the battery should still be > 13.0 volts. If that voltage does drop a little, rev the engine up to 2000 rpm and the headlights should go bright and you should see > 13.5 volts at the battery, if this happens your alternator is fine. The alternator cannot make the appropriate voltage (13-14.6 volts) and not have any current, it's a physics thing. Or if there is not enough current, then the voltage will drop.
your problem sounds like the classic problem of the battery sitting too long, sulfating, and you're not charging it properly back to 100%. Running the car for an hour to two will not charge the battery.
https://ls1tech.com/forums/general-m...ng-winter.html

also, a battery fully charge at 100% state of charge is 12.65 volts at 70F open circuit voltage, open circuit meaning battery is not connected to anything. If your battery is only holding 12.3 volts, after a proper charge, then it is most likely sulfated and has lost a lot of capacity. You said it tested good, so it is possible under certain conditions for a load test to be successful on a battery like that, but I would first assume whoever tested it did it wrong, or did not do a load test. if you had some jamoke at autozone test it you most likely wasted gas driving there, the battery is bad.
You could buy a good charger like a battery tender or batteryminder which can do equalization charging and do pulsing to reverse sulfation but that only works to a limited extent, if the battery is too far gone you're better off buying a new battery. And if you know the battery will go unused for 3-4 weeks or more at a time, then it will be cost effective to spend $70 on a good charger and maintain that battery for 5+ years versus a new battery every few years.

 

Is it not starting then? Charge the battery, just because it tests good does not mean it has a charge, the autozone testers dont work worth a **** either. The only real way to test a battery is to charge it for about 12 hours on a sustained charge and then load test it.

Have you checked other things on the car? Fuses, grounds, connections, check the water level in the battery(only use distilled water if its low).

 

The car starts, runs and drives fine. It does it at 12.5 volts which isn't right.

1FMF Open circuit Voltage = Voltage the alternator produces with no load. For the record the alternator CAN handle a short circuit current test or else it wouldn't be able to produced the one-hundred something amps advertised . The reason no one does a short circuit current test is because an AMP meter that will handle 100-200 amps is $$$. Generators, alternators, and transformers can be short circuit tested, batteries cannot be. I have designed a generator for an electrical engineering project. I just don't have access to the tools to measure that kind of power anymore.

Checked fuses, don't think it's relays. I don't hear any clicking oddly and everything seems to be working right. I agree it has to be the battery or the alternator. My neighbor gave me an alternator to test with just have to check the part numbers first. I figure that's a good test, throw another alternator at it see if it at least changes the problem. If not I am going to make O'Reily's replace the battery, tell them I don't give a **** if it "test" good.

Here is what I have done:

Test alternator at O'Reily's. No current shown, no voltage shown, just says "Good"
Test battery at O;Reily's, Charged battery, re-tested, tested good.
Tested alternator at local alternator repair shop. Tested good.
Checked grounds tightened one. Still showing low voltage.
Still staying with my low current theory.