Engine Battery Not Charging And Idle Speed 1100rpm

Discussion in 'Motorhome Chat' started by Mr Colpot, Jun 13, 2015.

  1. Mr Colpot

    Mr Colpot Funster

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    We went to go away today and got about a hundred yards up the road when I noticed the engine idle speed was higher than normal. I revved the engine a tad and the the battery light came on.
    We returned home and I measured the voltage on the Engine Battery with the engine running and it didnt change from 12.3v. Decided to abort the night away and called the AA. The AA Guy came and all appeared ok - battery was charging. I then explained I had plugged the EHU in to see if the Engine battery was charging on the EHU Charger and had left it in. We unplugged the EHU and the issue then reoccured - the engine idle speed went up and the battery light came on.
    The AA Guy advised that the alternator is faulty and needs replacing.
    I have seen threads about earth straps causing problems and am wondering if it may the issue here or something else.
    I am not sure why plugging the EHU in would cause the alternator to start working.
    Any advice/ideas welcome.
    Thanks
     
  2. daveandsan

    daveandsan Funster

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    The high idle revs might be because there is no load on the alternator, so could be faulty.
     
  3. DanielFord

    DanielFord Funster

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    I'd be inclined to check the alternator fuse first, if you are getting no output from it, that only costs about 50p

    [edit]
    There is also an exciter wire, usually a spade joint to the alternator, these can become corroded and cause intermittent charging.
     
  4. Mr Colpot

    Mr Colpot Funster

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    Thanks - it seems consistent though - with the EHU plugged in and the Engine running both batteries are showing 14v - I unplug the EHU and the alternator stops charging. I wondered about a fuse for the alternator but can find no mention of one in my handbook.
    Also - does anyone know how to open the bonnet if it gets stuck. I can hear the mechanism clicking when Mrs Colpot pulls the lever but as much as I try pushing and lifting the bonnet is firmly latched.
     
  5. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    With ehu connected the engine battery is receiving charge from the on board charger, with the engine running and ehu connected the engine ecu sees the starter battery at 14 volts and thinks the alternator is working so leaves revs as normal. When you disconnect ehu the battery voltage falls because your alternator is not charging so ecu ups idle speed to increase charge rate, when this fails to happen the ecu puts the battery light on. My diagnosis is failed alternator. Unlikely to be earth strap ( although not impossible) because the first symptom is usually poor starting not charging problems.

    D.
     
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  6. GWAYGWAY

    GWAYGWAY Funster

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    Does the revcounter run off the alternator on this engine, a lot of diesel engines do or is it from the impulse counter on the crankshaft.
    If it is off the alternator then ARE THE REVS actually up? and sound like they are or is it a false reading. If it sounds OK then the alternator might have a faulty winding. The EHU might just be coincidental or a currenet if feeding back through the diodes into the system, and giving the "increase". Worth a check.
     
  7. Mr Colpot

    Mr Colpot Funster

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    Thanks - the revs are actually up.
     
  8. Mr Colpot

    Mr Colpot Funster

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    Thanks Dave - I think the best bet is to get the local garage to replace the alternator under the MB&G warranty hopefully during the week. May leave the bonnet opening to them as well.
     
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