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Old 02-19-2011, 09:42 PM
 
Location: Chicago
38,691 posts, read 82,754,694 times
Reputation: 29172

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OK, so I know jack about automotive electrical systems. Yesterday I went to jump-start one of my cars with the other car. It jumped just fine and I drove it around for an hour and a half with no problem. Shut it off, and 10 minutes later it wouldn't start. So I went to jump it again today, started up just fine... but then when I took the jumper cable off, it died instantly. Jumped it again, same result -- started and ran just fine until I took the cable off one of the battery terminals. Is this a problem with the battery or the alternator? Or could it be either/both?
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Old 02-19-2011, 09:47 PM
 
Location: Banana Republic, LA
378 posts, read 927,024 times
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Sounds to me like its the battery, but I'll leave it to someone more mechanically inclined to make a diagnosis. Just wanted to say that if you take it to a place like Autozone, they offer free testing and will tell you if it's a bad battery or not.
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Old 02-19-2011, 09:47 PM
 
Location: Earth
4,220 posts, read 19,089,109 times
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Probably the batt is very drained, could be the alt. bad too. The way it's supposed to work is the batt powers everything and the alt. keeps it charged.

How many volts does the batt have w/o the cables on it? Should be 12.4 when fully charged.

p.s. could always just run the batt and the alt over to Idiotzone and have them check both.
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Old 02-19-2011, 10:01 PM
 
Location: Chicago
38,691 posts, read 82,754,694 times
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Quote:
Originally Posted by redbean View Post
Sounds to me like its the battery, but I'll leave it to someone more mechanically inclined to make a diagnosis. Just wanted to say that if you take it to a place like Autozone, they offer free testing and will tell you if it's a bad battery or not.
Kinda hard to get it there if it won't run. [ETA: Doh -- you mean the battery, not the car ] Fortunately there's a shop down the way who will pay for towing as long as there's at least $100 worth of work to it. And a battery alone would do it. I'm just trying to get a feel for what I'm getting into because it will be a few days before I can get it there.
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Old 02-19-2011, 10:12 PM
 
Location: Guangzhou, China
9,490 posts, read 11,817,788 times
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You need a new battery. Your current one is 100% dead and won't hold a charge.
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Old 02-19-2011, 10:18 PM
 
Location: Chicago
38,691 posts, read 82,754,694 times
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Quote:
Originally Posted by 415_s2k View Post
You need a new battery. Your current one is 100% dead and won't hold a charge.
I sure hope that's all there is to it.
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Old 02-20-2011, 12:10 AM
 
48,526 posts, read 75,935,879 times
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Souhnds like the alterntor is out;not charging the battery(which may already be damage by being discharged if not deep cycle type;and the laterntor is suplly elctricity once the battery power is removed. That is why you can jumo start a car with dead battery and it then runs on alternator whch also charges the battery. Have it tested.
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Old 02-20-2011, 05:27 AM
 
Location: Spencer, Ohio
365 posts, read 1,086,109 times
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Quote:
Originally Posted by Deez Nuttz View Post
Probably the batt is very drained, could be the alt. bad too. The way it's supposed to work is the batt powers everything and the alt. keeps it charged.

How many volts does the batt have w/o the cables on it? Should be 12.4 when fully charged.

p.s. could always just run the batt and the alt over to Idiotzone and have them check both.
You kinda messed that part up. Once the vehicle is running the alternator provides power to the electrical system, not the battery. You can run a car all day once it's started, without the battery... but you can't do the same without an alternator.

To the OP - Chances are the alternator is the problem... hence your vehicle running fine once it's piggy-backing off of the other car's charging system. I'm sure the battery took a beating though so you'll probably need a new one of those too.
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Old 02-20-2011, 08:39 AM
 
878 posts, read 1,580,249 times
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alternator
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Old 02-20-2011, 11:10 AM
 
4,711 posts, read 9,919,272 times
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I had the same thing happen a few years ago.

I always thought that, once started, the alternator would produce enough juice to keep it running. I replaced the battery and never had any more trouble.

I've since learned that a battery that is shorted internally can do this...apparently the alternator juice dosn't get through the battery to the engine electricals required for the engine to run.
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