Charging problem prado 120 d4d

Tuure Aug 11, 2019

  1. Tuure

    Tuure New Member I am in finland

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    Hello,
    I have a problem with charging.
    The voltage from the alternator is ok. But the batteries do not charge. The charging light is off. Where's the problem?
     
  2. StarCruiser

    StarCruiser Well-Known Member Supporter Guru I am in uk

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    What voltage do you get at the battery terminals? Should be 14.4v after starting.
    My first guess would be the alternator has a shorted diode that is pumping AC current in and draining the batteries over night. It could also be that your batteries are failing. How old are your batteries? Have you tried charging them with a battery charger, a C Tek charger is an excellent choice for this. More info needed.
     
    Last edited: Aug 11, 2019
  3. PeterLC

    PeterLC Active Member I am in belgium

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    Tuure, how do you know the battery is not charging ? Your battery may be defective. In that case it will probably have a high internal resistance. A battery with one bad cell will allow you to start when the engine is hot but you'll have difficulty when cold. That should be your first place to look.
     
  4. Tuure

    Tuure New Member I am in finland

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    The batteries are new. I have charged them by ctek. I can drive some days without charging. Voltage after start is 12.5 V and 2000 rpm little more than 13 V. ( The voltage is not normal I said incorrectly).
     
  5. Juddian

    Juddian New Member I am in great_britain

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    Sounds like the alternator has died, mine went exactly the same way, i hadn't realised it wasn't charging because twin batteries last a long time without re-charging in the summer, i twigged eventually like you i had no ignition light when it became slow turning over.
    Refurb alternator from a local auto electrical shop cost some £126, fitted myself.
     
  6. Tuure

    Tuure New Member I am in finland

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    Today I drived 250km with 5 stops. Voltage was 12.55 at morning and about same now?
     
  7. Tuure

    Tuure New Member I am in finland

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    12.55 when motor was off.
     
  8. PeterLC

    PeterLC Active Member I am in belgium

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    Most likely a problem with your alternator. The brushes for field excitation wear with time and are generally cheap and easy to replace. Using vernier calipers. measure the exposed brush
    length. Minimum exposed length is 1.5 mm, If the exposed length is less than minimum, replace.
    The voltage regulator IC in the alternator is also a suspect and in third place the rectifier diodes. If you have a current clamp meter for DC, now is the time to use it. After starting the current should exceed 40A for a minute or so and then drop to 10A.
     
  9. Tuure

    Tuure New Member I am in finland

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    I think that I will buy a new alternator. I change it by myself. Do you know what kind of the alternator must be? I would buy correct alternator.
     
  10. Simon5030

    Simon5030 Member I am in great_britain

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    Have a look at my post, might help

    https://www.landcruiserclub.net/community/threads/alternator.152466/

    Its a straight forward job once you have done it a few times :)

    Simon
     
  11. StarCruiser

    StarCruiser Well-Known Member Supporter Guru I am in uk

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    Clearly a faulty alternator. Not sure on the 120 but Nippon Denso was the make that most decent Japanese cars had from new. There should be a number and manufacturer on it somewhere.
     
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