Just had to replace a starter and a battery. took the starter to autozone and had it tested, didn't even spin so I know it was bad. installed new starter and still wouldn't turn. the new starter wouldn't work because of a dead battery. had the battery tested and the machine said good but low charge. so I got a new battery anyway. put the new battery in and it fired right up. I didn't run it long because I didn't know if it was running off the battery or not. is it as simple as disconnecting the battery with the car running, and if the car dies then it is a bad alternator. I was told you shouldn't do this by an old timmer because it could mess up a good alternator. I don't want to kill my new battery, but I need to know before I cruze it again.
Low tech way, with the motor running stick a screwdriver to the back center of the alternator. If it sticks good it's putting out a charge, no stick no charge.
Put a multi-meter (volts) on the battery while running. Getting 13.5 volts or so indicates it's charging. Tony
While its running attach a volt meter to the large terminal on the rear of the alternator and ground the minus lead from the meter(probably black in color) to ground
Another low tech way is to start the car, disconnect the positive battery cable, then turn on the lights. If the car dies, alternator is bad. (Alt supplies power and without battery +, no power = car off)
I did this, and while running it had 14.45 volts so I believe its charging. thanks, I completely had a brain fart and after reading this I said you dummy I know this. it's been awhile since I've had battery problems. thank you and thank the hamb!!!!
Voltage at idle can be a bad indicator. Alternators can also fail by overcharging and destroying batteries.
That would typically be the fault of the voltage regulator, not the alt itself. Voltage at idle is a good indicator of general condition, IMO.
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