testing the alternator

[xlMcMlx DsM]

So i came to my talon on monday, to find that the new battery put in by the old owner(less than a year old) was dead. Now im pretty sure the alternator is the cause. My buddy at school told me that to test his alternator in his '88 celica turbo, he started the car and then pulled both the terminals off the battery. And that if it died, its the alternator. Because isnt the alternator supposed to produce enough amps to keep the car running? and is this a good way to test it?

 

[wcpierson]

Go to Walmart and buy a voltmeter, you can get one for like $20 then have your friend jump start your car. If the alternator is working you should be running somewhere around 14v. The battery itself should only be 12v. If you can get it running and get to an autozone they can test it for free. Also check the alternator relay under the hood...It blew on me once and caused my car to run straight from the battery even though the alternator was fine.

 

[19Eclipse90]

Don't bother with Autozone or other auto stores to test your alternator. I had a bad one and everyone, even a straight up alternator shop, tell me it was fine, that it all tested fine. But on the car, it would drain the battery. Use the voltmeter. The battery while the car is off should read between 12-13volts and while it is running should be as stated above 14 close to 15volts. If it is not, check the voltage at the alternator while the car is running. It should also read 14 close to 15 volts.

 

[luv2rallye]

Although pulling the battery cables off will show if the alt is working, the generated spike also can destroy an ECU. Simple alt test: http://www.dsmtuners.com/forums/showthread.php?t=226323

 

[xlMcMlx DsM]

I have a voltmeter here. So I'll go test that when I'm not doing homework I got an extra battery in my 1.8 so I'll use that.

 

[90 Eagle Talon]

The thing with the voltmeter, is this always true because my battery reads around 12.8 when runnning and about 11v when off does this mean that the alternator is going bad. But I can start my car up every morning and drive to school, but the other day my brother who is learning to drive cutoff twice getting out of the driveway and then it would not start and we had to push it back in, at least this did not happen down the street though.

 

[Tsi_User]

I got my alternator tested today at Advance auto parts and told me it was bad it was at about 20-22 Volts and Max is 15 so yea mine is bad and need to replace it im wondering if it messed up my computer too

Lets put it this way, last time my alternator diet it overcharged the battery to to the point where the alternator was smoking and the battery was shooting acid out of it... And it didn't mess up the ECU.. you should be fine.

Nice color 1ga btw

 

[19Eclipse90]

The thing with the voltmeter, is this always true because my battery reads around 12.8 when runnning and about 11v when off does this mean that the alternator is going bad. But I can start my car up every morning and drive to school, but the other day my brother who is learning to drive cutoff twice getting out of the driveway and then it would not start and we had to push it back in, at least this did not happen down the street though.

The thing with the voltmeter is always true. If you aren't reading those numbers, you've got a little bit of checking to do. Easiest, and what I would suggest, is taking your battery to an Autozone or other free tester. They can tell you if your battery is bad, which is more of what it sounds like to me than an alternator. If it isn't, read the voltage output AT the alternator. If it is isn't where it is supposed to be, you've got an alternator that is on it's way out.

An alternator's output charge is regulated by the voltage regulator.

>>The regulator is the brain of the charging system.

It monitors both battery and stator voltages and depending on the measured voltages, the regulator will adjust the amount of rotor field current to control alternator output.
>> from http://www.autoshop101.com/trainmodules/alternator/alt111.html

If the regulator fails, the alternator will have the tendency to overcharge. Pretty simple concept

 

[xlMcMlx DsM]

the alternator seems to be the original one, and the car has 170,XXX miles so i think getting a new one would be a good idea anyway. But im gonna put in the battery from my eclipse and run it to school and run the ARBST tester on it. That'll tell me if the alternator is bad or not. thanks guys, this is really appreciated