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Old 01-19-2010, 08:26 PM   #1
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quick question about alternator

I have been having problems keeping my battery charged. I have got a new battery from Autozone and the problem still returns.

If I let the car sit for a day or so, the battery is very low.
I left the lights on tonight when I got pulled over, and I had to get a jump from DPS after only 10 mins of sitting.

I got a warning for no front plate if anyone is wondering.

Anyway, my question is.....

Should my car continue to run if I disconnect the battery. This is a quick way I use to test the alternator in the old days. The thought is that the car only needs the battery to start. The alternator should put out enough juice to run.

With the car started, battery diconnected, it idles rough.......

If I turn on the lights the car dies.

I dont have a multimeter.
What should the alternator be putting out at idle?

Thanks,
James
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Old 01-19-2010, 08:58 PM   #2
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I had 12.1 when I just changed my Alternator tonight. Car started up fine. Then I had about 13.3 or so. You should look for atleast 13 volts to be going into the battery for it to be charging.
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Old 01-20-2010, 08:25 AM   #3
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I don't believe disconnecting the battery with the car running is a good idea. I think I read somewhere that it will immediately kill the alternator by taking out a diode or two. It sounds as if your alternator may be the problem.
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Old 01-20-2010, 10:02 AM   #4
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Yea, I think it is the alternator as well. This is my second one. It is 4 yrs old.

I am going to get a multimeter today and see what the output is. I am planning on going with a 4 inch underdrive pulley in about a week, and if the alternator is low now, it will be worse then.

How hard is it to replace the alternator? I have done it on cars and trucks many times, but this car is so cramped it may be different.
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Old 01-20-2010, 10:58 AM   #5
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With the car started, battery diconnected, it idles rough.......

If the alternator wasn't dead before, it is now. The battery acts as a voltage buffer for the electronic system; you remove the buffer and the spikes kill the system.
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Old 01-20-2010, 11:26 AM   #6
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Well checked the alternator with multi meter. It seems to be fine. output is 13.8V with 45 amp.

I guess it is the battery...Its is only 6 mo. old and it is the third battery I replaced.


Could there be a regulator or solenoid that I should check next?
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Old 01-20-2010, 11:50 AM   #7
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Have you tried charging the battery on a charger? Don't assume that just driving around is getting you to full charge. When a battery is fully charged, after you let it sit for a few hours to dissapate the surface charge, you should read a voltage of 12.75 V. Anything lower than that (e.g. even 12.6 V) means the battery isn't fully charged,

If your system voltage is 13.8 V, your alternator is working. If you start with a fully charged battery and it's not staying at 12.75 V after you drive the car, the battery needs replacement.
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Old 01-20-2010, 03:43 PM   #8
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Did you test your alternator output with maximum load? Put your headlights on, heater fan on high, stereo on, and anything else you have that pulls juice, then see what the output is. With this load it may no longer be in the normal range, indicating an alternator problem.
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Old 01-20-2010, 04:03 PM   #9
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And when (if) you charge your battery with an external charger, you need to disconnect the battery leads from the car & leave it being charged for at least 12 hours......
Then do your voltage check.
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