Cool noob discovery - stronger 9V batt charges weaker one in parallel

Discussion in 'General Electronics Chat' started by Avalanche Breakdown, Apr 28, 2007.

  1. Avalanche Breakdown

    Thread Starter Member

    Mar 22, 2007
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    As an experimenting kind of kid, I discovered that two 9V batteries plugged into each other just creates a lot of heat pretty quickly, and ruins the batteries. Fast forward to the present, and I've uncovered a new find... for me anyway.

    I built another one of my battery driven, LED flashlight projects this week, which uses two 9V's in parallel for double runtime. The only two 9V's in the house checked out at 7.9V, and the other was 8.9V. Ten cool points to all who guess where they both ended up after a few days.

    Don't laugh too hard... it was a cool discovery... lol. And now it sorta' makes sense why it happened, but it wasn't expected. Of course, the flashlight did not have to be on for the V's to balance out.

    Ya' learn something new every day. :D
     
  2. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    8.4V from everything I have always heard about batteries in parallel.
     
  3. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    from transformers to generator it is very necessary that whenever you connect two voltage sources in parallel that the voltages should always be equal. for
    this not only shud they have same amp but also must be in same phase and have same frequency hope u dont try this one at home :)
     
  4. Avalanche Breakdown

    Thread Starter Member

    Mar 22, 2007
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    Ten cool points for knightofsolamnus!
     
  5. Eddy Kurent

    Member

    Apr 9, 2007
    18
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    Ever hear of Ohm's Law?

    Ever studied what voltage appears across resistors in parallel?
     
  6. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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  7. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    Here's the thing...

    One battery was charged by the expense of another. Just change both batteries at the same time. Power supply engineers who deal with batteries will squawk at this. Saftey!
     
  8. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    There are some nasty chemicals inside of some cells.
    At the minimum, please wear some kind of eye protection
    We'd not like it if you were to become the newest Darwin Award candidate!
    It's always better to learn without the burn!
    Be careful.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Just so we all know - the Army recommends using two 9 volt batteries shorted together to make an IR range reference at night. Less obvious than leaving a small fire burning with a sign posted "please stand here until you hear the mortar rounds coming".
     
  10. Avalanche Breakdown

    Thread Starter Member

    Mar 22, 2007
    20
    0
    Next time I call in an evening airstrike, I'm using that tip!

    subtech - LOVE the Darwin Awards, but don't worry. I won't be showing up in them anytime soon... I think. :D
     
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