I know this is a newbie question, but how do you determine if the alternator is bad? It keeps killing the battery. I have had the battery checked and it is good. I have several other problems to talk about, but i'll start with this one. Anyone???

 

You may very well have an alternator problem, but it is just as likely you have something drawing current while the car is off, killing the battery. A dc clamp on ammeter is rather expensive, but that is the best way to test. As a "triage" method, you can observe the battery voltage off, then running. If it rises .2 to .5 volts while running , it is probably not the alternator. You can test the current draw when the car is stopped by connecting an inline ammeter while off, wait about 30 minutes and look for current greater than about 20-25 ma. If you have that, something is drawing current when it shouldn't.
Good luck

 

So, I recharge the battery and check voltage before I crank it and then while it is running. Will the car not keep running with battery disconnected if the alternator is putting out the proper voltage? Used to check alternators this way before computer control, but not sure if it will work on today's cars.

 

Yes, it does work, but I would not recommend it due to the voltage spikes that occur when you have no battery load. They could destroy any number of modules.

 

Ok. Will try the voltage test. I have an alternator on the way just in case.

 

Tested battery. Before cranking 9.6 volts. When running 13.9 volts. Alternator is doing the job. Getting a battery today. Thanks for the help.