Charging a car battery question.

  1. Feb 10, 2013 #1
    Hey. Was jump starting and charging a car battery a couple of days ago for the first time. I connected the positive of the bad battery to the positive of the good battery, then connected the negative of the good battery to a solid metallic, non-painted part of the engine on the bad car, or the body frame.

    My question is: How is this a closed circuit? Is the negative terminal of the bad car's battery connected to its "solid metallic parts/body frame?"
     
  2. jcsd
  3. Feb 10, 2013 #2

    marcusl

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    Yes, the negative is grounded just as you said.
     
  4. Feb 10, 2013 #3
    Thank you for the quick reply. My mind is now at ease.
     
  5. Feb 10, 2013 #4
    Ok now a follow up question if you don't mind. Why then not connect the good battery's negative directly to the bad battery's negative?
     
  6. Feb 10, 2013 #5

    marcusl

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    Batteries produce hydrogen gas bubbles as they charge, and this can be vigorous for a fully discharged battery. Connecting to chassis ground keeps any sparks away from the battery and flammable gas.
     
    Last edited: Feb 10, 2013
  7. Feb 10, 2013 #6
    Thank you.
     
  8. Feb 10, 2013 #7

    jim hardy

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    Follow your battery wires.
    Most GM cars have a positive post near the battery for jump-starting. It'll be underneath a red plastic pop-up cover.
    Sure easier than trying to grab that battery side-post terminal, and safer too as marcusi pointed out.

    I like to connect negative to a substabntial piece of metal on the engine. I figure starter is bolted to engine block, so starter's heavy current doesn't have to flow through a potentially weak frame wire on its way back to my jumping battery's negative..
     
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