How do you know if the alternator is bad?

Answer 1

TestBefore paying money for a new alternator (which I was about to do today), be sure to have the alternator tested. As many people suggest, Auto Zone, and other parts suppliers, will test it for free. You may have bad connections into your alternator...make sure they are secure and free of corrosion. You might also simply need to tighten the alternator belt. A loose belt will also prevent the alternator from charging the battery. Cable testTry this: With the vehicle running, disconnect the negative cable from the battery. If the vehicle keeps running, the battery could be bad. If the vehicle dies, the alternator is probably bad. Most major auto parts stores can test batteries and alternators.

Note - the above answer states that you should disconnect the negative cable from the battery. 'The correct answer is to remove the POSITIVE cable not the NEGATIVE.

constantly deadYour battery is there for starting purposes only- once you start the car, the alternator/generator takes over, and runs the cars electrical system (and recharges the battery)- if you start your car and then disconnect the battery, if your alternator is good, the car will keep running. bad alternator and the car will die. note that if your alternator is bad, your car can run off the battery for a while till the battery dies. sure sign of bad alternator = constantly dead battery. Additional Answers

• start the car the remove positive battery terminal if car stalls or idle drops really low alternator is bad

• My battery indicator light came on, but the car would still start and the alternator belt was intact. I tested the alternator with a volt meter and sure enough it was bad.

• Battery continually going dead. Best thing to do is drive the car to an Auto Parts store and have the alternator load tested.

• If you do not have a voltage tester bring it to a repair shop and have them test the alternator. Puts out between 13-14 volts. If under 13 it is probably bad

• You can always start the vehicle and disconnect the battery. If it dies, your alternator is the problem. If not something else might be the problem.

• start or jump-start the vehicle. Remove jumper cables after it's started. Use a volt meter to find out the voltage at the battery. If it's below 13.5 VDC, the alternator is probably bad. Take it to an auto parts retailer and they'll usually test it for free.