Alternator out????

[Anonymous]

having a problem keeping battery up, car runs for a while 30 minutes or so, then it dies... the alt. light stay on all the time, so i'm thinking there is a problem with it, maybe it's out or not running properly??? what can i check to see if it's working or it needs rebuilt??? or do i just have to take it off and have it checked at a alt. shop??

 

[Anonymous]

Go and buy yourself a cheap voltmeter at radio shack (Wal Mart might have them, or an Auto Parts Store), they have them for not very much(digital is easier to use than analog(needle)).

With the car running check the voltage across the battery posts, red lead on the positive terminal and black lead on the negative terminal.

Make sure the meter is set up to read DC volts and that the range is either set up for or being read on the correct scale (usually between 10 and 20 volts on analog meters).

With the car running you should be getting anywhere from 13.5 to 14.5 volts.

The extra 1.5 or 2.5 volts above the 12 volts for the battery is what charges the battery while you're driving.

With the lights and other accessories on it might drop a little, but shouldn't go below 13 certainly.

**If you're going to own an old car, better either get rich, or learn how to work on it yourself.

Best of luck,

Dave

 

[Anonymous]

thanks for the info...learn something new everyday, that is why i love this board.....big help

 

[Anonymous]

You're welcome, I'd like to hear about what you found out.

Dave

 

[Anonymous]

Most auto parts shops can check out or test either the alternator or the voltage regulator.

The only times I ever had charging problems on a Ford, it was because there was a lot of corrosion on the regulator terminals.

 

[Anonymous]

cost me 25 bucks...when they put it on tester, wasn't doing what it supposed to, changed the regulator and brushes and when they tested it it's now working fine at the shop.... i put it back in, Alt light still stays on, and it runs fine, let it run for 30 minutes and drove it up and down the driveway for a little while and when i turned it off the battery was at 50%, it was at 100% when i started... i'm taking that as it's still not charging...it should of dropped that far if it was charging....could it be bad battery, or where would i look for bad connections from alt to whatever it supposed to be hooked too...all the wires going from the alt, look good and have good connections..what else can i do or check??????

 

[Anonymous]

Go back and try what I said to do in the first reply to your problem. The most sure way to start troubleshooting a problem is to check it ON YOUR CAR while it's doing what it's doing......for 25 bucks you could have gotten a half decent voltmeter. :!:

 

[Anonymous]

it could be the battery, ive had 2 batteries with problems, one tested full on the charger but wasnt putting anything out when i needed power (interior lights wouldnt evern turn on) i'm sure this was caused by the wire that the moron before me left dangeling to ground itself (it was the second battery so nothing was connected to it.) the other battery wouldnt hold a charge for very long, u could boost it and then it would die and u could charge it and it would only be good for a little while, this might be your problem. The alt light goes on when the voltage drops below a certain point, i think its 11V, not to sure. so the battery could be your problem. usually when u have a bad alt problem u want to change the battery because one can effect the other negitavely.

 

[Anonymous]

Check the fusible links - they are chunks of formed rubber in the wires attached to the starter solenoid.

If the wire inside melts (they are like a fuse) they will feel mushy and will not conduct.

The heavy wire from the alternator to the starter solenoid has a fusible link in it.

 

[Anonymous]

i charge it and it runs good for a while, then it won't hold the charge....what is the right size battery for these mustangs?? how many cranking amps should they have??? i'll also check the fuse links as well...thanks guys

 

[Anonymous]

The stock batteries back in the day were most likely less than 500 amps. I ALWAYS run the largest battery that will fit in the tray.

If your battery charges up fine, starts the car well, but slowly runs down you still have problems with the charging system on the car itself.

Do a little trouble shooting on the car (check all wires between regulator and alternator) then get back to us.

 

[Anonymous]

I just had an alternator problem on a newer car. Battery had run down since I did not use the car in a few weeks. With a low battery, my multi-meter showed the alternator was only putting out 12.5 volts max at elevated rpm's. So I was wondering if it was truly bad or not. I took it to Autozone and it tested OK. I reinstalled the alternator and charged the battery. A week later, I got stranded with a low battery. Charged the battery fully and took it and the alternator into Autozone for a test. Both tested OK and my idiot light still had not indicated any problems. My multi meters were still showing only 12.5 volts. I was not impressed with the Autozone Test machine. The silly thing just flashes pass or fail. There are not quantitative readings of the alternator output. I decided to buy an alternator and give it a try thinking the alternator was weak. Now I have the 13.5 volts I am accustomed to seeing. Hopefully my problems are fixed now, I need to check the battery voltage again after driving for a few days now. I guess the moral of the story is that an Autozone tests may not be a definative test, and I should have believed my multi-meter.
Doug

 

[Anonymous]

the moral of the story is that an Autozone tests may not be a definative test,

That, and they don't put it under ANY load. A TRUE alternator tester has a strong electric motor, like 2-5 HP to spin the alternator and a carbon pile to build resistance to run the alternator under a load. That little 1/4 HP thing at autozone can't run an alternotor under load. It is pretty worthless.

 

[Inline6Merc]

The diodes are bad if you drive it and the battery is drained. Diodes allow current to pass throught them but when there bad they can get stuck open and allow the current going from the battery to just drain out throught the ground cable.

Later,

Curtis