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Meaning of BATERRY polarity

Discussion in 'General Electronics Discussion' started by lefam, Dec 9, 2010.

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  1. lefam

    lefam

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    Nov 18, 2010
    Hi guys!

    I am pretty new to electronics. I am having some problems with my first circuits and I am now suspecting that maybe my understanding of battery polarity is wrong.

    So, my question is: in batteries (example 9V alkaline) the (+) terminal is +Vs, and the (-) terminal is GROUND?

    (+) terminal = +Vcc?
    (-) terminal = GROUND?

    I have been using (-) like +Vs and (+) like GROUND. Probably the cause of failure in my first circuits.
     
  2. davenn

    davenn Moderator

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    why would you have even considered connecting the - to the + ?? thats not logical :confused:
    + to + and - to - always

    reversing the polarity of the power if a surefire way of killing the intergrated circuits etc

    No ( - ) terminal = Negative, always call ( - ) the Negative terminal, see next comments

    Negative ( - ) would normally be Ground (tho there are some exceptions)
    you would usually only see a Ground label if the ( - ) part of the circuit was connect to the chassis of the equip, which was then connected to ground via the "earth" (ground) lead of the mains power lead.

    cheers
    Dave
     
    Last edited: Dec 9, 2010
  3. lefam

    lefam

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    Nov 18, 2010
    To power a circuit (for example the 555 IC), what should I connect where they ask for +Vs (PIN8 in the case of the 555 IC)? The (+) terminal from the battery or the (-) terminal?
     
  4. davenn

    davenn Moderator

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    after reading my comments in previous post... what do you think the LOGICAL connections would be ? :)

    Dave
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    As davenn says, the "+" is a clue.

    + to +
    - to -

    so + to +Vs is obvious

    Now, some circuits require +, - and 0v, in which case you need 2 batteries, but I won't even confuse you with that just yet.
     
  6. lefam

    lefam

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    Nov 18, 2010
    So, that's why my circuits where not working (because of using - terminal as +V). I tried to build a 555 LED flasher and it was not working. I failed also with transistor circuits.
    Now my transistor circuits are working.

    I have one curiosity: why do the electrons flow from the (+) terminal to (-) in the battery? Are they following the conventional flow? I am confused because in electron flow (the real flow) electrons flow from (-) to (+). What is the meaning of polarity of batteries?
     
  7. davenn

    davenn Moderator

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    Electrons flow from Negative to Positive that is the "real" electron current flow.
    electrons have a negative charge.

    The positive to negative is what is called conventional current flow ( its misleading)

    Polarities of a battery ( or any other supply) well you have to have a positive and a negative. you cannot have 2 negative terminals (or 2 positive terminals) ... there would be no resulting current flow.

    Dave
     
  8. davenn

    davenn Moderator

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    yeah we will leave split supplies to another day haha ;)
    hopefully he is finally sorted out for a single rail supply :)

    Dave
     
  9. Laplace

    Laplace

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    Apr 4, 2010
    Don't get too concerned about the flow of electrons. For all practical circuit analysis and design purposes, just assume that current flows from plus to minus. About the only time you will need to consider electrons is in the study of quantum electronics and the physics of the P-N junction between doped semiconductors where you will mathematically model the flow of electrons and the flow of holes (i.e., the presence of absence.) And never connect the minus (-) power supply terminal to the +Vcc pin of your IC.
     
  10. lefam

    lefam

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    Nov 18, 2010
    So in a battery, the (+) terminal is the most negative terminal (with excess electrons) that flow to (-) (lack of electrons)?
    Do the batteries use conventional flow in the terminal indicators?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    No, the + terminal is + and the - terminal is -

    FORGET about current flow, conventional or otherwise.

    Just connect the positive on the battery to the positive supply rail of your circuit, and the negative to the negative supply rail.

    It's really that simple. there are no tricks.
     
  12. Laplace

    Laplace

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    Apr 4, 2010
    @lefam: "So in a battery, ....."

    It is not useful to think about what happens in a battery because then you have to think about electrons and how electrons behave in terms of chemistry. That is a chemistry issue, not an electronics issue. Focus your attention not on the battery but on the circuit to which you connect the battery. Now, you may question why I assume that current flows from plus to minus in a circuit, especially since it would be equally valid to assume the reverse. I am a member of the cult of positive flow because virtually everyone else is also a member of the positive cult. Can you imagine the level of cognitive dissonance if believers for positive flow had to work together on a project with believers for negative flow? That is too horrible to contemplate!
     
  13. lefam

    lefam

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    Nov 18, 2010
    Thank you guys
     
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