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Thread: Grounded Positive Battery Terminal

                  
   
  1. #1
    Senior Member JC5's Avatar
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    Grounded Positive Battery Terminal

    Just to say right off the bat, I goofed. When changing the battery on my 2003 530 I accidentally grounded the positive battery terminal. There was a nice spark when I did this, and now it seems there is an electrical issue.

    When the car is running at idle, I get 14VDC at the battery, but when the blinkers, window switches and such are used, the voltage drops to 13.4VDC. This can be seen in the various lights through out the car fluctuating (dimming, then brightening). The car never really completely dies due to electrical system failure.

    Is there a a common thing, or point to strart, in trying to locate the source of the electrical fault? Or is this going to be a trip to the dealer? I have a fair amount of DIY experience, so pulling something apart to diagnose will not be a big deal.
    Supercharged '03 530
    Thinking about tracking down an e28 535is

  2. #2
    Quote Originally Posted by JC5 View Post
    Just to say right off the bat, I goofed. When changing the battery on my 2003 530 I accidentally grounded the positive battery terminal. There was a nice spark when I did this, and now it seems there is an electrical issue.

    When the car is running at idle, I get 14VDC at the battery, but when the blinkers, window switches and such are used, the voltage drops to 13.4VDC. This can be seen in the various lights through out the car fluctuating (dimming, then brightening). The car never really completely dies due to electrical system failure.

    Is there a a common thing, or point to strart, in trying to locate the source of the electrical fault? Or is this going to be a trip to the dealer? I have a fair amount of DIY experience, so pulling something apart to diagnose will not be a big deal.
    Take the battery out of the equation. If you grounded the positive terminal, chances are that you destroyed the plates, etc. in the battery. Sounds to me like the battery is internally shorting out causing the alternator to work overtime. The ground on our cars are chassis ground, so if you just shorted the positive terminal to the frame (or other metal) no electronics should be harmed, just the battery due to over discharge. Sniff the battery - does it smell like sulfur?

  3. #3
    Senior Member JC5's Avatar
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    Thought about that. The battery was 4 years old anyway, so I replaced it. The problem persisted.
    Supercharged '03 530
    Thinking about tracking down an e28 535is

  4. #4
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    Maybe you spiked the diodes in the voltage regulator and limited the avilable current control, and soon will go bad.

  5. #5
    Senior Member JC5's Avatar
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    I actually though I had toasted something in the alternator, so I had it rebuilt with OE parts and tested. One of the parts that was replaced was the regulator. The problem persisted after the rebuild.
    Supercharged '03 530
    Thinking about tracking down an e28 535is

  6. #6
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    Had an alternator rebuilt as well and had the same effects (dimming) but corrected itself a quarter second later. Don't know if it does it anymore because I don't drive that car and haven't asked the wife.

  7. #7
    Senior Member JC5's Avatar
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    That sounds exactly like mine. The voltage immediatly recovers.
    Supercharged '03 530
    Thinking about tracking down an e28 535is

  8. #8
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    hhmmm, let me take wifeys car out for a drive in the snow and see whats up. I'll be back...

  9. #9
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    Well, the lights brightened a very slight bit with sudden high rpm but that's all. It's like the new stuff broke in and works alright.

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