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Battery/Alternator

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  • 27-07-2016 3:58pm
    #1
    Jamie2k9
    Registered Users Posts: 10,674 ✭✭✭✭


    Sister used a car to jump start battery on an Air Compressor recently and her car stopped yesterday because it started running off the battery and not the alternator as a result (or other way round?).

    I used another car a few weeks ago for the same and wanted to know is there a way I could check if the same thing has happened before it might stop.

    Thanks


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    #2
    biko
    Registered Users Posts: 81,223 ✭✭✭✭biko


    The battery supplies electricity to everything.
    The battery in turn is charged by the alternator.
    The alternator only works when engine is running and preferably actually driving.

    So if you used the car's battery to jump something you should drive the car afterwards to charge battery back up again.


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    #3
    Jamie2k9
    Registered Users Posts: 10,674 ✭✭✭✭Jamie2k9


    biko wrote: »
    The battery supplies electricity to everything.
    The battery in turn is charged by the alternator.
    The alternator only works when engine is running and preferably actually driving.

    So if you used the car's battery to jump something you should drive the car afterwards to charge battery back up again.

    Hi, it was jumped last Monday and did a lot of driving since then but stopped yesterday so could it of taken a week for a battery to go flat.

    Is there anyway to know if the battery is charging while driving?

    My car did it some time ago and drivers probally more than hers but am just a little worried it might stop now.

    BTW haven't a clue about cars as you can see.


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    #4
    exaisle
    Registered Users Posts: 2,673 ✭✭✭exaisle


    Why was it jump started last monday? Presumably because the battery was flat.

    Go get the battery checked at a tyre & battery place. They have a meter there that can check batteries.


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    #5
    nd
    Registered Users Posts: 1,855 ✭✭✭nd


    if you have a multimeter check the voltage at the battery when the car is running. If it reads about 14.5 volts or so the alternater is ok. If it's reading aboit 12 or less your alternator isn't working right.

    If you don't have a multimeter you could just try disconnecting the battery while the car is running. If the engine stops running your alternator isn't working.


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    #6
    Mech1
    Registered Users Posts: 5,081 ✭✭✭Mech1


    nd wrote: »
    if you have a multimeter check the voltage at the battery when the car is running. If it reads about 14.5 volts or so the alternater is ok. If it's reading aboit 12 or less your alternator isn't working right.

    If you don't have a multimeter you could just try disconnecting the battery while the car is running. If the engine stops running your alternator isn't working.

    Dont do this!!!


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    #7
    nd
    Registered Users Posts: 1,855 ✭✭✭nd


    Yes actually don't. Another test is turn on everything electrical in your car when the engine is running.. And your internal lights.Rev the engine a bit. If your alternator isn't working your internal lights will slowly get dimmer. If they brighten as you rev the engine the alternator should be good.


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    #8
    biko
    Registered Users Posts: 81,223 ✭✭✭✭biko


    Mech1 wrote: »
    Dont do this!!!
    Explain why so OP can learn.


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    #9
    Avns1s
    Registered Users Posts: 3,422 ✭✭✭Avns1s


    biko wrote: »
    Explain why so OP can learn.

    Because if the alternator was working before you disconnect the battery while the car is running, there's a very high probability it wont be working afterwards!!


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    #10
    BrianD3
    Registered Users Posts: 8,297 ✭✭✭BrianD3


    I got a multimeter in Maplins a while back and it assisted me for diagnosing a battery problem in one of my cars and an alternator problem in another one. Saved me money and hassle.

    Multimeter for 13 quid in LIDL soon
    http://www.lidl.ie/en/Offers.htm?action=showDetail&id=43325


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    #11
    porsche boy
    Registered Users Posts: 1,560 ✭✭✭porsche boy


    Avns1s wrote:
    Because if the alternator was working before you disconnect the battery while the car is running, there's a very high probability it wont be working afterwards!!

    How do you figure that?
    A common way of replacing a battery is to do it while the car is running. This negates having to retune the radio and set clock.
    The battery supplies the power to start the engine, after that the altinator supplies power, through the battery to all the electrics.


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    #12
    jimmyw
    Registered Users Posts: 3,383 ✭✭✭jimmyw


    porsche boy wrote: »
    How do you figure that?
    A common way of replacing a battery is to do it while the car is running. This negates having to retune the radio and set clock.
    The battery supplies the power to start the engine, after that the altinator supplies power, through the battery to all the electrics.

    What?............ thats not correct.You will feck up the alternator doing that, and you will send way too much current to the components.If you dont want to lose the radio stations then hook up a power pack to the cigar lighter.


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    #13
    porsche boy
    Registered Users Posts: 1,560 ✭✭✭porsche boy


    jimmyw wrote:
    What?............ thats not correct.You will feck up the alternator doing that, and you will send way too much current to the components.If you dont want to lose the radio stations then hook up a power pack to the cigar lighter.

    How will I 'feck up the altinator' though? Power is going from the altinator, nothing is returning to it. All power going to components is fused so any spike in power would blow a fuse if that was to happen. As I say I'm just curious as to how the altinator wall be 'fecked up'?


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    #14
    jimmyw
    Registered Users Posts: 3,383 ✭✭✭jimmyw


    porsche boy wrote: »
    How will I 'feck up the altinator' though? Power is going from the altinator, nothing is returning to it. All power going to components is fused so any spike in power would blow a fuse if that was to happen. As I say I'm just curious as to how the altinator wall be 'fecked up'?

    Because the Alternator needs feedback from the battery to know when the battery is full and if you have no batt, it thinks that the battery is flat, and it will throw out way too much current.Any manual will tell you not to do this.

    I found this out myself on a tractor alternator when I put a voltmeter on it one time with the wiring connected and I got 14 volts, I then disconnected the wiring to find the volts had jumped to about 60 volts I think.

    I would strongly advise not to do this.


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    #15
    Avns1s
    Registered Users Posts: 3,422 ✭✭✭Avns1s


    porsche boy wrote: »
    How do you figure that?
    A common way of replacing a battery is to do it while the car is running. This negates having to retune the radio and set clock.
    The battery supplies the power to start the engine, after that the altinator supplies power, through the battery to all the electrics.

    Sure, you go right ahead and do that if you wish, but please don't put it about here as good practice. It's not!!

    If you want to keep power to the radio, then connect another battery via the cigarette lighter or even use jump leads to connect it to the +ve terminal and an earth on the car.

    Disconnecting the battery when the car is running will cause a surge and fry the rectifier and other components in the alternator. It may charge afterwards but may also discharge the battery through its components when the car is switched off. Perhaps others may have a better explanation of the technical reasons.

    In any case, the proper and correct advise is do NOT disconnect the battery while the car is running.


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