Thread: Voltage drop from alternator

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  1. #1 Voltage drop from alternator 
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    Ok so I am not a mechanic by any means. I have recently has issues with my car dying due to battery drain. I first assumed that it was the alternator and replaced it. Still not getting enough charge to the battery. I've had the battery checked out, and both the new and old alternator are only putting out 12v or less while the car is running. I'm pretty much at a dead end as to where my knowledge is and I wanted to see if anyone could help me with ideas to figure this dilemma out. I appreciate all the help and I'm sorry if this is a repost of any other problems just like it.
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  2. #2 Re: Voltage drop from alternator 
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    If the battery is dead, the alt wont do its job.

    Where are you taking your measurements from?
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  3. #3 Re: Voltage drop from alternator 
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    I've had oreillys charge the battery about three times as well as putting it on the charger at home too after it gets drained. I'm using a multimeter and testing the output from the alternator at the battery terminals with the car running. Also using the ground on the battery and putting the positive lead to the connection on the fuse box under the hood. Getting the same voltage in both places. I don't see it being a bad alternator seeing as I've had them tested, so it was a bit of a waste that I bought a new one, but, oh well.

    What I'm thinking is that I'm getting some resistance in the circuit somewhere....problem is, I know jack about the wiring and need some help.
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  4. #4 Re: Voltage drop from alternator 
    Poppin 'em thangs mechguy's Avatar
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    It sounds like a "ground loop" or ciculating ground type of problem, where ground locations are at different potentials and you have current flowing through them. Check the voltage between the alternator terminal and somewhere on the engine with the engine running. It would be nice to see how much current flows through the alternator at idle, but most people don't have an ammeter for such. Alternatively, it could be a bad connection somewhere. Check the power wiring for frayed, oxidized wire, or loose connections.

    So, have you performed any electrical work to this car that may be causing this? Any aftermarket accessories, even a security system? How quickly will the battery die after last using the car?
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  5. #5 Re: Voltage drop from alternator 
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    I haven't added anything to the car, no. Actually this all seemed to start after a bad rain storm in which my car suddenly began leaking inside under the passenger dash onto the floor board. I've since sealed around the cowel on the car preventing water from going into the air box beside the drain on the firewall. I've teste it by running a water hose full blast on that area, which it would leak before, but now t doesn't.

    Anyways, there is the potential that maybe something in that area got shorted out, there is a fuse box in the glove compartment and I've checked the fuses with no luck.

    I'll keep trying with the meter to find variations in the voltage.

    Oh and it takes roughly 20-30 minutes driving after charging the battery although I'm probably not charging it completely as my charger is old and doesn't give you any idea how much charge your battery has.
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  6. #6 Re: Voltage drop from alternator 
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    Would an alt rewire simply fix this? just run a wire from the alt to the fuse box terminal and see if the cuts out the bad part.
    97 GT white 4 door-SOLD

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  7. #7 Re: Voltage drop from alternator 
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    I am gonna try that, I just had both alts tested and they're both good, confirming my suspicion. So, I'll give residing the hot wire from the alt to the fuse panel and see how that works, but something tells me it's more complex than that, because that's just my luck lol
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  8. #8 Re: Voltage drop from alternator 
    GTX Level Member cerick08GP's Avatar
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    Just going by what you have said, I can pretty much guarantee the fusible link down by the starter is blown. Hence your alternator isn’t “putting out” jack that your car can use. Although many people never have an issue with it, the electrical system is half genius and half village idiot. That said, I’d bet if you ran a 6 gauge wire from the alternator to the distribution box lug you would be golden. I would probably disconnect the existing wire alternator wire just to be sure.

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  9. #9 Re: Voltage drop from alternator 
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    Ok so, and sorry for my lack of knowledge, I need to runs 6 gauge wire from the alternator to the fuse box, correct? And can you explain what a fusable link is exactly?
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  10. #10 Re: Voltage drop from alternator 
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    Quote Originally Posted by NyteSniper View Post
    Ok so, and sorry for my lack of knowledge, I need to runs 6 gauge wire from the alternator to the fuse box, correct? And can you explain what a fusable link is exactly?
    Basically you need something like this :
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  11. #11 Re: Voltage drop from alternator 
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    Awesome! Thanks! I'll give this a shot and see how it goes.
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  12. #12 Re: Voltage drop from alternator 
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    Hm, once the car is on, I think the ground switches to the engine/transmission. You may want to check that ground - it could be loose or something.
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  13. #13 Re: Voltage drop from alternator 
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    Thank you cerick and ejouie, I've done what you guys said and now I'm getting 14V output. Working good now! Thanks for all the help everyone, couldn't have done without all of your help!
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  14. #14 Re: Voltage drop from alternator 
    GTX Level Member EJOUIE's Avatar
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    your very welcome.
    97 GT white 4 door-SOLD

    Cherry 2005 Impala LS- Front and Rear GMPP Strut Tower Braces
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  15. #15 Re: Voltage drop from alternator 
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    Quote Originally Posted by NyteSniper View Post
    Thank you cerick and ejouie, I've done what you guys said and now I'm getting 14V output. Working good now! Thanks for all the help everyone, couldn't have done without all of your help!
    Thanks for actually getting back to us man, glad I could help.

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