connected battery wrong way round. help

Discussion in 'Electronics' started by jamie-ann, Apr 2, 2014.

  1. jamie-ann

    jamie-ann New Member

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    W202 1997. My battery had been fully charged over night and I was rushing to work and connected terminals other way round. They sparked and there a bit of smoke from engine and all lights on cluster went on.

    I might have tried start it I'm not sure till my son suggested I check terminals and I realised my mistake.

    Car started fine and I managed to drive 20 miles to work. Evetything seems working except radio wont come on. I have couple fuses so I replaced necessary fuses according to fuse sheet under bonnet but still not working.

    More worrying is battery red light came on and stayed on during whole journey. What does mean? Is my alternator goosed? What's simple test for this and if alternator wasnt working would battery have managed 20 miles withought dying?

    Worried sick. Battery was fully charged but seems weak the 2 times I have started th car during my coffee break 5 mins ago
     
  2. p3tchy

    p3tchy Hardcore MB Enthusiast

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    Simple answer is yes the battery being fully charged would have managed to supply enough power to drive maybe for a few days but it sounds like you've killed the alternator. Or the reg/rec side of it anyway.
     
  3. Sp!ke

    Sp!ke Administrator Staff Member

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    I would say that 20 miles with no alternator is as much as you can expect.

    I wouldn't try driving home until you have it checked or you might get stranded somewhere dangerous.

    Do you have breakdown cover? My suggestion would be to call the AA or similar and have them check it out before going home time and recover you if necessary.
     
  4. OP
    OP
    jamie-ann

    jamie-ann New Member

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    Is there a simple way of testing alternator or the regulator for peace of mind? Total novice and need and appreciate all the help I can get guys
     
  5. DSM10000

    DSM10000 Hardcore MB Enthusiast

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    Check the output with a voltmeter, amy garage can do this.
     
  6. OP
    OP
    jamie-ann

    jamie-ann New Member

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    Got rest of day off thats how worried I am. Started the car drove 1 mile and fan, indicators etc all gone. Pulled over and after idling for a bit engine died
     
  7. Sp!ke

    Sp!ke Administrator Staff Member

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    I did try and warn you... :wallbash:
     
  8. Ted

    Ted Hardcore MB Enthusiast

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    You will have blown the main rectifier diodes in the alternator, so consider it to be dead.
    You say the red light is on permanently. There will be at least one thick wire and a thin wire to the alternator.
    If you remove the thin wire (engine OFF bit ignition ON) and the light goes out (which it will), the alternator is faulty.

    If you are lucky this will be all that you have fried.

    Hope you get it sorted ok.

    Edit: why were you charging the battery in the first place?
     
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  9. fast28

    fast28 Active Member

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    I had reverse polarity calamity on my W215 CL500, same problem with the alternator not charging the battery. I even purchased a new alternator in anticipation that it was goosed. In fact the main 150amp fuse on the alternator to battery cable had blown down in the driver's footwell, this fuse is not part of the main fuse box circuits and uses a "midi" size fuse rather than lower amperage blade fuses. Not sure on the W202 though. Other than this fuse blowing I blew a transistor in the ABS controller, the heating resistor pack was blown and about 7 fuses had blown on the radio and other random circuits.

    [​IMG]
     
    Last edited: Apr 2, 2014
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  10. Ted

    Ted Hardcore MB Enthusiast

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    Good point there.
    The main feed to the alternator may just be protected by a fuse.
    If this blew before you fried the diode(s) your alternator may have survived.

    Check on the big thick wire (red I think) to the alternator that it is permanently live.
    Use a testlight not a voltmeter.
     
  11. OP
    OP
    jamie-ann

    jamie-ann New Member

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    Got the AA out and guy said alternator not charging battery. He connected it to his truck for 20 mins then hooked up a booster pack. This allowed me to drive to a Halfords centre used by AA. I have got the parts and warranty scheme luckily. They said will call me once looked at it. Worried they find out what happened and AA refuse to pay

    Was charging battery because car had been sitting there SORN due to illnesd till today
     
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  12. camerafodder

    camerafodder Hardcore MB Enthusiast

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    Ted used to be in bomb disposal!










    :D
     
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