Electron/current flow in a 9v battery backwards?

Discussion in 'General Electronics Chat' started by diggler001, Jan 28, 2009.

  1. diggler001

    Thread Starter New Member

    Jan 28, 2009
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    0
    Hi all, first incredible site, I am learning so much here (teaching myself electronics and all about circuits is better than any book I have tried!)

    The way I am learning about current flow/electron flow is that it flows from the negative side of the power source to the positive (electron flow theory).

    Last night on a bread board, I wired up a 9v battery a resistor, and an LED.

    The (-) ground of the battery went to the resistor, which went to the cathode (flat side) of the LED and then the anode went on to the (+) terminal of the 9v battery. But I got nothing. Until I flipped the positive and negative wires on the battery then the LED lit up.

    Wired this way, it means current is flowing from the + terminal of the battery to the cathode of the led, instead of the other way, right?

    This sounds like the battery is labeled using "conventional flow" instead of "electron flow". Is this the case and is it like that for all batteries? Or do I need to go back to square one because I have it all wrong in my head :)

    Thanks!!
     
    Last edited: Jan 28, 2009
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
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    Uhh, no.

    Nine volts are just like all other electronics. Can't speak for yours, they could be labeled incorrectly, but this is what they look like.

    [​IMG]

    Generally, Red is positive, Black is negitive. When dealing with circuits, conventional circuit flow is not your friend.
     
  3. diggler001

    Thread Starter New Member

    Jan 28, 2009
    4
    0
    Thanks Bill! Despite triple checking my connections I must have made a mistake in my circuit last night. I just did a real simple test of wrapping a resistor to the cathode of the led, and put the anode to the + battery terminal and resistor/cathode on the - and it lit up as it should. I'll have to set it up on the bread board again tonight and figure out what it was only working in reverse last night :)

    Thanks again!
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    For what it's worth, everyone does that one time or another. Just don't let the magic blue smoke out.
     
  5. italo

    New Member

    Nov 20, 2005
    205
    1
    lEDS ARE DIODES i don't know what a flat side is but look for the longer lead on the led as positive.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,764
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    I prefer to look for the cathode on the inside of the LED, since I cut most of mine for protoboards. I'm not aware of any exceptions, though as many types there are I'm sure there are some. The flat side is usually the cathode, which I also look for.

    [​IMG]
     
  7. diggler001

    Thread Starter New Member

    Jan 28, 2009
    4
    0
    mystery solved! Turns out the 9v battery snap leads I picked up at a surplus store were wired as black -> positive red -> negative! Silly me for thinking it was the usual black is negative lead :)

    ***update** (just noticed your above post after I posted this hehe)

    As to the "flat side" on my leds, on the cathode side they flattened the edge of the plastic cover on the led so you can see which is cathode in the leads have been cut.

    Like this...
    [​IMG]

    Thanks again for the help!!
     
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