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Flat Black King
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Discussion Starter #1
I recently changed my alternator and had the battery disconnected for 3 days. Now that its all connected my battery wont stay charged to turn my car on. anyone know the problem
 

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Are you saying you're running the car with the new alternator, and the battery won't stay charged?

If so.....there is a problem with the new alternator, or the connections. Or your battery itself is failing. Hook up a volt meter to the battery while the car is running.....it should read around 14V. Have the battery load tested at Auto Zone for free.

The only other possibility....something is staying on after the car is not running, causing the battery to go dead over-night.
 

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Flat Black King
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Discussion Starter #3
Autozone tested it all and says its all good. had it on a charger all night and still didnt charge. I think something is staying on to make it die i just dont know what. The battery is brand new
 

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Still confused.....You charge the battery with an external charger, and it's still dead? Or you try to start the car and the engine spins, but won't start?
 

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Flat Black King
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Discussion Starter #5
after i put the alternator on i charged the battery over night. Wouldnt start the next morning. Now everytime i leave the car off for hours, i have to jump start it cause the battery is dead. Autozone check the battery, starter and alternator and said they are good. Just not sure whats making the battery die.
 

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Assuming the Autozone testing was accurate, which is a big assumption. you are correct that it sounds like you have a battery drain problem. The best way to diagnose it is to use an ampmeter to measure the current flow out of the battery while the car is shut off with the key out of the ignition. This requires you to disconnect the positive wires from the battery and put the ampmeter between the battery and the positive connectors to force any current drain to flow throw the ampmeter. DO NOT ATTEMPT TO START THE VEHICLE WHILE DOING THIS! The current flows drawn by the starter will burn-out or blow the fuse of the typical low-current ampmeter you would use to do this.

Once you confirm that there is an inappropriate current drain from the battery using the ampmeter readings, you can then, one-by-one, pull and replace fuses. When you find the fuse which stops the current drain when pulled, you will have identified the basic circuit/wiring which has the problem. You them need to check everything on that circuit to determine what is causing the drain.

Now, if you do not have the equipment or expertise to do this, as I suspect may be the case, then the best you can do is check for obvious current drain problems such as an interior dome light not going out, etc.

P.S. If you did the alternator replacement yourself, I would strongly suggest that you double and triple check the connections you made to ensure it's all hooked up right.

P.P.S. I would also double-check the Autozone testing with a basic test of measuring the voltage at the battery (a) while the vehicle is running, (b) immediately after shutting it off, and (c) after it has sat for 1 hour, 2 hours, 3 hours, etc.


Hope that helps.
 

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Flat Black King
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Discussion Starter #7
I shall do that tonight. If i can find the ampmeter. Would putting a a bigger fuse in the car then what is normally supposed to be there for example, the blinkers need a 5 amp fuse and i put a 15 amp fuse. would that cause it too?
 

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Or disconnect the big red wire from the back of the alternator, then see if the battery will stay charged. Because of the fact that this started when the new alternator went on, I'm guessing it's bad- bad diodes. So when the car's not running, the alternator just sits there and draws current. Lots of it.

BTW, an alternator with a bad diode (there are 3 in there) will still charge and might test out all right.
 

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Flat Black King
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Discussion Starter #10
well what im gonna do is clean the terminals and the post on the battery and see if that helps if not ill try all that stuff up there.
 

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> Would putting a a bigger fuse in the car then what is normally supposed to be there for example, the blinkers need a 5 amp fuse and i put a 15 amp fuse. would that cause it too?

Nope.

The size of the fuse has no effect on current flow, unless the current becomes high enough to "blow" it.
 

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> I'm guessing it's bad- bad diodes. So when the car's not running, the alternator just sits there and draws current.

Excellent suggestion. The latest thing worked on is quite often the issue. If only one diode is bad, the alternator would still work, just with a lower output.
 

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Flat Black King
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Discussion Starter #13
so that means i need a new alternator? I checked it 2 times at autozone and both said was fine.
 

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If disconnecting the alternator stops the battery from being pulled down, then yes, you probably need another new alternator.

I don't know what to say about autozone's methods, if they even test for backflow. Maybe as long as it's putting out some current they figure it's all right. Especially if they just sold it to you.
 

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Flat Black King
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Discussion Starter #16
well i read online different ways to test it and im gonna do it when i can but right now i disconnect the negative terminal when im gonna be somewhere for along time like work and then when i leave i put it back on and it starts
 

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Why don't you try what I said? I'm quite sure you'll find your problem without any further fooling around. In fact, you'll be able to tell right away, you won't have to wait to see what the battery does-

1. Make sure the ignition is turned off and everything else is off (dome lights, etc).Disconnect the battery neg cable. As you seperate the terminal from the post, you will probably see a fairly healthy arc- that's the current that's sucking the life out of the battery.)

2. Disconnect the fat red wire from the alternator. Position it so the end can't short out against anything.

3. Go back up and just touch the neg terminal to the post again, If I've guessed right the arc will be dramatically less. (there'll still be a very small arc, that's the normal draw from the clock etc.) If this is the case, the alternator is bad.

4. Double check yourself, Reconnect the neg batt cable, then take the fat red alternator lead that you disconnected earlier and touch it back onto it's terminal on the alternator. There must be no arc at all there. If there is- bad alternator confirmed.
 

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Flat Black King
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Discussion Starter #18
good info i shall try that and test it then tell u. where did u get this info and has this been proven to show the alternator is bad?
 

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You're smart to be skeptical! This is the internet after all. I got this info from 40 years of fooling around with cars and trucks. I have been a professional mechanic at times, a fleet service manager, and a fleet maintenance director, but not currently, and mostly on 18 wheelers. I was an auto mechanic way back in the late '60s, and a pretty good one at that, if I do say so myself.

Diodes (there are 3 of them in there) act as electrical check valves, allowing current to flow in one direction, but not the other. Their sole function is to allow the current generated in the stator (that's that coil of reddish wire you see if you look into the alternator) to flow out to the battery when the alternator is spinning, but not to let the coil draw current from the battery when it stops.

If you do end up carting this thing back to autozone, you'll probably have to tell them specifically it's sucking the battery down, otherwise they'll probably just spin it, see some current being produced, and declare it good.
 

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I think I said it before, but that's a really good idea and thing to test out. I completely agree this can point out the problem. mad props Blurvfocus.
 
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