Flat battery

Discussion in 'Tech/Mech General' started by irnbru, Jul 13, 2016.

  1. irnbru

    irnbru Funster Life Member

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    Im asking this for a friend of a friend who is parked up at my friends alongside me. I have suggested joining MHF but as they need help to learn what a post is I shall ask the Q.

    They have a Mh around 1998, drove through Ireland and had a flat battery one morning. A garage replaced both alternator and fan belt. They drove up from Cairnryan to Glasgow today. After stopping half hr on arrival the battery was flat.
    Being female the only info ive learned is from all you guys...I put voltage meter on battery without engine running..11.78. But when engine started it only showed 11.66 which is even less and not more.

    Any suggestions? Im guessing duff battery.
     
  2. Stealaway

    Stealaway Funster

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    I would say duff charging ------ for some reason. With engine running I would expect to see 14.+ at the batterys
     
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  3. Jaws

    Jaws Funster Life Member

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    How long after you started the engine did you wait before checking the voltage, and how long did you check it for ?
    If you started it and checked it straight away and only for a few seconds the battery will have taken a big hit to start the lump and may well have come up a lot higher as time went by..
    Restart it and let it run for a few minutes and check again.
    If it is still low then the alternator they had fitted is duff.
    Also ask how old the battery is.
    There is often a reason alternators fail.. a really old battery ! The charging system will try and bring a duff battery up to spec and because it ( the battery ) is well past it, it will never reach a charged state, so the system will keep on working flat out to try and bring the battery up.. a nasty vicious circle !
     
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  4. pappajohn

    pappajohn Funster Life Member

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    Are they sure the alternator was renewed or did they just pay for something they never got.

    If it's only showing 11.66v with the engine running it sounds like the alternator has failed....or the belt has snapped/come off.

    If there is no charge at all, the battery will show a lower voltage when running as the starter has just taken a little bit more out plus any electrics needed to run the engine....electric lift pump, fuel solenoid etc.
    Volts out, no means of putting volts back in.
     
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  5. irnbru

    irnbru Funster Life Member

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    Ive retreated back to my MH now...Big brother on tv and its getting dusky. Will try again in the morning if it starts. I did ask if there was a way they could divert the ehu to charge starter battery but they dont know.
    They have now tried to get on MHF and only now do I appreciate how everyone is not pc savvy. I know where my 2mor is going ..
     
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  6. pappajohn

    pappajohn Funster Life Member

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    Not like you John.....
    The alternator will output at least 13.8v as soon as the engine is started regardless of battery state.
     
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  7. funflair

    funflair Funster Life Member

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    At 1998 could it be an externally regulated alternator and possibly the problem was never the alternator.

    It could be a job for somebody a bit auto elec techy.

    Martin
     
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  8. andy63

    andy63 Funster

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    Was chatting to Sandra and the lad earlier and I asked that question but suspect even at that age the alternator will have the rectifier and regulator built in..
    I was wondering if the battery was bad a failed cell for eg could that be the reason for the voltage appearing so low even with the engine running...
    Mentioned that he could check the earth lead off the battery...
    As well ..
    The red light has been on on the dash and remains on when the engine is running rather dim but still visibly glowing... which suggests a charging fault but the alternator and belt are new..
    Hope you don't mind me butting in on your thread Sandra. ..
    Andy
     
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  9. funflair

    funflair Funster Life Member

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    If the red light is on the alternator is not generating a voltage higher than the battery, I think.

    Martin
     
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  10. pappajohn

    pappajohn Funster Life Member

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    Never heard of one of those....except recent vehicles with 'smart charging' controlled by the ECU.
    Only thing with an external regulator was a dynamo.
     
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  11. andy63

    andy63 Funster

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    So can a failed battery cause the alternator to show a low voltage ???
    Could check between battery positive and alternator output to see if there is a volt drop there ie bad connection and similarly the negative battery terminal and alternator body for volt drop...
    But not sure if those conditions could prevent a normal charging voltage from alternator..
    Andy
     
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  12. funflair

    funflair Funster Life Member

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  13. mitzimad

    mitzimad Funster

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    looked like the dynamo regulators without the coils on top but unlikly at that age very much late seventies
     
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  14. funflair

    funflair Funster Life Member

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    Am I older than I think.


    Don't answer.

    Martin
     
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  15. pappajohn

    pappajohn Funster Life Member

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    Agreed, every site I look at is for Ford, jeep, gm etc from around 1968 to mid/late 70s.
     
  16. pappajohn

    pappajohn Funster Life Member

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    OK we won't..... :LOL:
     
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  17. TheBig1

    TheBig1 Funster Life Member

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    double check the charge wire hasnt fallen off the new alternator
     
  18. Jaws

    Jaws Funster Life Member

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    Nooo.. it SHOULD output 13.8 volts but if there is a short between plates it will be held down to maybe 12.4 !

    Having said that if the charge light is glowing then that would indicate the alternator is simply not slinging enough juice up the rope to the battery .. so almost def a duff alternator..

    Just a though though.. If you have any jump leads put one between the battery -ve and the engine block.
    A poorly earthed engine can cause the same issue, and as it is a rare fault the garage that fitted the belt and genny might have easily missed it.. or indeed left the earth strip off when fitting the alternator !
     
  19. irnbru

    irnbru Funster Life Member

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    I wouldnt know where to look. :eek: and I have a sore back so I have just passed on all your great info. Battery does look as if its not been off in a long time but man said battery was good as it was checked when alternator was replaced. He has the old alternator.

    He did ask if he got stuck again could he use his leisure battery to start his vehicle with jump leads. I said yes but he would ruin his leisure battery if he done it too often...Did I get that right:sick:
     
  20. andy63

    andy63 Funster

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    Without knowing what he was using as a leisure battery that's hard to answer but I'd have said the same :)..
    I used to connect jump leads from my leisure to the start battery on my fist van as a matter of course on a cold morning... It always worked fine (y)
     
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