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car electronics question - jump starting — Parallax Forums

car electronics question - jump starting

JavalinJavalin Posts: 892
edited 2007-11-21 12:13 in General Discussion
Hello All,

A question.· Why when jump starting a car with a dead battery from either a booster pack, or another vehicle, do the instructions always read:

1) Connect positive to positive
2)·Connect negative (booster/other car) to engine block of the dead vehicle - NOT the minus terminal of the battery

Seems odd as i've always done Neg-2-Neg, then Pos-2-Pos both jumpstarting and generally connecting batteries to stuff.

So the questions:
1) Why positive first?
2)·Why not neg to minus on the battery?

Only thing I can find on-line is when fitting a battery, that if you connect the positive first and accidentally ground the terminal - then without the neg attached nothing will happen.· Obv with the neg battery terminal connected it'd go bang!

Cheers,

James

Comments

  • RDL2004RDL2004 Posts: 2,554
    edited 2007-11-21 12:06
    Well, I remember reading that making the negative connection second and away from the battery, then disconnecting it first, was to avoid causing any sparks near the battery. Lead acid batteries generate hydrogen gas when charging and the idea was to minimize any possibility of an explosion. To me this seems a very unlikely thing to happen, I'd be surprised if you could do it if you tried, but better safe than sorry.

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    - Rick
  • Desy2820Desy2820 Posts: 138
    edited 2007-11-21 12:10
    You connect the positives first, as you said, just in case the loose, unconnected cable end touches any bare metal·and shorts out whichever battery is connected at the time.

    You avoid connecting the negative at the dead/weak battery in case of a spark.· Batteries produce hydrogen gas and a spark near the battery can cause an·explosion.· All car-type batteries·produce hydrogen gas and will have a vent somewhere, even if it's not obvious.· You make the final connection away from the battery so any spark that occurs is far enough away to not explode the hydrogen gas.· (Battery chargers are subject to the same problem, with the charger unplugged, connect it to the battery, then plug it in.· Reverse the procedure to disconnect.)

    I hope this helped!

    ·
  • JavalinJavalin Posts: 892
    edited 2007-11-21 12:13
    Hi Both,

    Interesting - thanks

    James
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