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daughters Corsa D 2010 new Alternator still not charging the battery

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  • [Corsa D] daughters Corsa D 2010 new Alternator still not charging the battery

    Hi All,
    just replaced the alternator (and battery) on daughters 2010 1.3cdti corsa D and i'll still not seeing any increased V at the battery at 2000rpm , just shows 12.6V ? BAttery light come on and goes off as it should when starting the car. Pulley belt tension looks to be good too. Any pointers of any relays, fuses ( but cant see anything in wiring diagrams ) or anything else to check or try would be appreciated.
    cheers

  • #2
    Welcome to the Forum.

    Using the starter motor will cause the battery voltage to fall slightly, as soon as the engine starts, the alternator should 'replace' this voltage - Before you go any further, try leaving the headlights switched on for a couple of minutes, this will pull the battery voltage down and you should then get at least 14.0 v at the battery positive terminal when the engine is started.

    If the new alternator is displaying the same symptoms as the old one ( only battery voltage when engine is running), it would suggest one of three problems (1) The new alternator is faulty - quite possible but not that likely (2) The thin (blue/white) wire to the alternator has some problem (3) The thick (red) wire from the alternator to the battery has a problem.

    With a test light (rather than a voltmeter) check that the bulb is as bright when connected between earth and the large alternator terminal as it is when connected between earth and battery positive - If not, then there is high resistance in the cable or its connections.

    Disconnect the alternator thin wire and connect your test light between battery positive and the small alternator terminal. Start the engine and see if the battery voltage now goes up above your 12.6 v

    The test light puts a small load on whatever you are checking, so if there is high resistance there, the light will not be bright, whereas a voltmeter would still read battery voltage. - You can easily make up a test light with an old (but good) bulb holder and a pair of wires.


    Regards

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    • #3
      many thanks for the response, further update, all wiring tests good between alternator and battery etc.. apart from lead from ECU to alternator (preexciting circuit i believe) is not showing a V as it should. Had friend at garage double check and he says all wiring checks out fine but ECU has deff been wet so suggests its a water damaged ECU. HAve now seen ECU damage is very common due to placement of ECU in the scuttle panel below windscreen but the "no charging of the battery" doesnt seem to be a common symptom of a wet damaged ECU. But guess its possible if that part of ECU damaged ? Anyone know if i can jump a constant V wire directly to the preexciting circuit ?? or are there any relays or fuses that supply part of the ECU, but this seems unlikely as car is fine in all other aspects or anyone seen this issue before ??
      cheers

      corsa d 1.3cdti (2010)

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      • #4
        If you were to connect a low wattage bulb (say 2.2w) between battery positive and the alternator sensing terminal (the wire that you speak of), the bulb should light.
        Unlike dynamo's, alternators do not have any 'residual magnetism' (although they sometimes 'acquire' a little with age.
        The absence of residual magnetism means that they need to have the rotor winding excited before they will deliver a charge, this is normally done via the 'ignition' warning light, so the small current passed by the 2.2w bulb would be sufficient to initiate a charge.
        Once the alternator is charging, its built in voltage regulator then supplies the rotor with the required current.

        DO NOT disconnect the alternator main output wire (the thicker one), or the battery terminals whilst the engine is running. To do so may well cause a 'voltage spike' and one thing that electronics don't like is a spike in the voltage, which can do great damage.

        If you decide to change the ECU, rather than buy a new one, there are people who will test and report on the old one, quoting a repair price - just Google 'ECU Repairers.'

        Regards

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