Testing alternators is more then just voltage, you can't just tap it with a DVOM and make a determination. I absolutely despise parts store electronic testers, are the convenient and easy to use yes. Are they accurate I think not so much, maybe 50%. Impedance testing is not very accurate to me, I mean a dead short, dead failure yes. If an alternator is at 12v running, yes it probably has an issue, but all the partial failures is hard to test.

A battery and charging system alike need to be put under working load in the conditions to give you a proper result. To truly test an alternator it should be ran on a test bench, which are few and far between anymore. A good carbon pile load tester is the next best option. For batteries and alternators both. I get frustrated get batteries warrantied. They come out with their impedance tester and go oh nope battery just fine. Well no bring it out to my house when its -35 and been sitting a couple days. I'm not suggesting one go and invest in all these tools, its just a matter of having you're own thought process when having an auto store "check" components. I've had a Schumacher hand held carbon pile forever and its served me quite well in diagnosing charging systems and batteries. I have have a dinosaur snap on carbon pile cart that can really put things to the test if needed also.

Sometimes I think auto store testers have two settings, warranty and customer sales......

 

A "new" fellow co working showed me his battery "load tester". It's one of those electronic ones with no real resistance to check it. I told him to get a real load tester. You can do a "full field" test but it's not a good idea to do on modern (electronic controlled ) vehicles. There is a section in the service manual where they test it with a rheostat(bypassing the regulator) to see if it's putting out. Basically the same as the full field test but it allows you to give it partial field with the rheostat.

 

Thanks so much for all of your responses! I really appreciate the help!
You guys are understanding correctly, since putting in the new battery about 6 months ago, I haven't had any problems with it at all. The part I was concerned about was that 2 autoparts store testing machines had said it wasn't functioning correctly, which to my limited knowledge, made me think it must be overcharging my new battery, cause if it wasn't charging it enough, that would be very apparent. It sounds like yall are saying that's not the case, so I'm going to quit fretting about what a testing machine says, and just keep driving my truck. 😁
Thanks again, guys!
Courage

 

I would would have asked what's it doing to not pass? If it's an overcharging that's not the alternator. It could still charge but not be up to where it should be putting out. There are diodes in alternators, Usually when ones goes it creates a parasitic drain on the battery. Other times it won't but the diode/s are not working and output will be a little less. The diodes convert ac power to dc.

 

I finally broke down couple of years ago and bought a computerized system tester. My old one finally quit working. It was old when I got it 50 or so years ago and it finally died. To test the system, you have to load test the battery and alternator. A lot of parts stores just test for voltage. Not amperage.

Keep in mind the saying "If it works, don't fix it".Unless you subscribe to the Red Green motto, "If it works, you're not trying!".

 

I think I did ask one of the guys, and he assumed that it must be overcharging it, since it was still starting on its own, but I don't think he was 100% sure...
That makes sense about needing to test for both. Eventually I'dike to get setup to do that kinda thing on my own, but at this point, that will have to wait.
Sounds like a good idea to just leave it alone, since its working! Guess I get to thinking about things a little too much sometimes and can get overzealous... 🤷🏼‍♂️🤦🏼‍♂️