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Thread: battery is at 12.5 volt when "charged"

  1. #1
    Variable Bitrate
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    battery is at 12.5 volt when "charged"

    hey guys. i really need help here. in my car i have two batteries ( battery 1 and battery 2. ) recently, i upgraded an installed a battery isolator. now i have the following problem:
    when my car is not running. the battery1 is at 11.9 volt, BUT the battery2 is at 7.8 (pretty dead).
    when the car is running, the alternator outputs 13.8v (as normal), BUT cause of the battery isolator, the other two battaries read 12.2 volt each... so, i guess they do not charge at all?? what can i do to solve this?? better alternator maybe??



    p.s don't bother answering " you should change alternator, go buy one that costs 1.000.000 euro so it has no voltage drop" or anything like that, cause i really dont think it as "help" ...

  2. #2
    Constant Bitrate
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    Sounds like your batteries are funky or on the way out.

  3. #3
    Variable Bitrate
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    the battery 2 (that with the car off is at 7) yes. but the other one is good. besides, i did not have the slightest problem before the isolator

  4. #4
    Constant Bitrate
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    Isolators have a diode or two and that will result in a 0.6 volt decrease (minimum) available to charge the battery.

    A typical lead acid requires 14.2 minimum to charge correctly and fully charged, open circuit should read 13.6 volts, 2.2 volts per cell.

    The regulator in the alternator might be funky also.

    I won't say alternator as you don't want to hear that.

  5. #5
    Variable Bitrate
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    my car is prety old (1992) so i guess it has a "normal" altarnator, without any adaptive regulation. is it possible to install a "clever" or whatever its called regulator, to increase the altarnators output?

  6. #6
    Constant Bitrate
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    Quote Originally Posted by settra View Post
    my car is prety old (1992) so i guess it has a "normal" altarnator, without any adaptive regulation. is it possible to install a "clever" or whatever its called regulator, to increase the altarnators output?
    Here is one way:

    http://www.smartgauge.co.uk/alt_mod.html

    You might look around for a rebuilt alternator or have the regulator in yours replaced (the diodes usually get replaced also).

    IMO replace the diodes first, that is rebuild the alternator.

  7. #7
    FLAC SNOtwistR's Avatar
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    The 7v battery is bringing the other down, disconnect the bad battery and toss it, it's only doing damage to the other parts of your system. here is how you should have it wired. (excuse the stick drawing) SNO
    Name:  isolatorwire.jpg
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  8. #8
    Variable Bitrate
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    but i have only 2 batteries? also, i would agree that the bad battery sucks all the ampere from the alternator, but i dont think it is getting charged at all (cause as soon as i turn off my car, my inverter starts beeping (meaning it has no power on it). ) and even after long trip, the 2nd battery is dead after i turn off..

  9. #9
    FLAC SNOtwistR's Avatar
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    Ok so you only have 2 batteries and 1 is bad you already have your answer the isolator is isolating your main battery from the bad battery when car is off your bad battery will not come back to life it is done like dinner and if you keep driving with that bad battery you will have to replace your alternator sooner than later. SNO

  10. #10
    Constant Bitrate
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    A "bad battery" usually will not charge as that is one of the faults they can show, besides being a drain.

    The bad one is just loading the system to the point neither battery is getting charged and one never will.

    You may have already damaged the alternator.

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