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positive and negative

Discussion in 'Electronic Repair' started by meirman, Jan 17, 2005.

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  1. meirman

    meirman Guest

    I almost can't believe it, but after 35 years, I still get confused
    about positive and negative. Sorry to bother you, but I just can't
    remember.

    I'm replacing a bridge rectifier with 4 separate diodes, and I know
    where the negative should be. If I put one diode on one AC wire, and
    another diode in the opposite direction on the other AC wire, and if I
    set the VOM on 200V DC, and I put the common/negative/black lead from
    the voltmeter on the unconnected end of one diode, and the
    positive/red lead on the other diode, and the needle moves to the
    right (I get a positive reading) does that mean the diode with the
    black wire on it is putting out negative?

    That's what I think, but I'm not sure.


    If I went by the silver/grey band on one end of the diode, would that
    end be the positive or negative end?

    These are all laid out parallel to each other and taped together, with
    narrow white paper tape on one end, and red paper tape on the other.
    This means that the end with the red tape puts out positive voltages,
    right?

    Thanks.

    Meirman

    If emailing, please let me know whether
    or not you are posting the same letter.
    Change domain to erols.com, if necessary.
     
  2. James Sweet

    James Sweet Guest



    Connect two diodes together at the striped end, that'll be your positive
    output, connect the other two together at the non-striped end, that'll be
    your negative output, now connect the two free pairs together in the middle
    and apply AC across those.
     
  3. meirman

    meirman Guest

    In sci.electronics.repair on Mon, 17 Jan 2005 06:42:51 GMT "James
    Thanks a lot.

    I haven't done it yet, but I'm sure that will work.

    (And of the ones which had never been used yet, the striped ends were
    the ones connected with the red paper tape, which makes sense. Red =
    plus.)


    Meirman

    If emailing, please let me know whether
    or not you are posting the same letter.
    Change domain to erols.com, if necessary.
     
  4. JURB6006

    JURB6006 Guest

    Connect two of the diodes together by the cathodes (banded end), connect the
    other two by the anodes (obviously the non-banded end).

    At the junction of the two banded ends you get positive, the negative is
    supplied by the aforementioned anodes.

    NOW LISTEN, IF YOU DON'T KNOW WHAT YOU'RE DOING DON'T DO IT ,,,,
    unless you use a small 12 volt tranformer or something, stay away from those
    mains.

    When you connect the ends you'll have AC applied to both an anode and a cathode
    at all times.

    This is called full-wave rectification.Positive and negative cycles are always
    sent to the proper output pins, of course, because of the diodes.You are
    basically building a "full wave bridge rectifier".

    Again, if you don't know what you're doing, at least in electrical safety, DO
    NOT DO IT. Also, make sure the diodes you are using are of the same or higher
    ratings.

    To sum it up, I'd rather just order the right friggin part. And, if it's mains
    rectifiers, don't do it at all, or on an SMPS. This is important.In some cases
    you really need the right part.

    JURB
     
  5. meirman

    meirman Guest

    In sci.electronics.repair on Mon, 17 Jan 2005 06:42:51 GMT "James
    Second reply. Posted and mailed.

    Well, you were right of course, and the tiny air compressor is fixed.
    I bought it and a lawn mower at a junk yard for 20 dollars. Fixed the
    lawn mower somehow without spending a dime (although it may need a
    helicoil when next spring comes and I try to mow a whole lawn with it.
    The mower looks brand new and the closest model to it sells for 175
    dollars.

    The bridge rectifier had shorted, I guess, and burned out a trace on
    the circuit board. Then it blew the fuse. I replaced the fuse, ran a
    wire in place of the circuit board connection, and put in 4 diodes.
    But I had all the stuff so it didn't cost anything. The compressor
    sells for 75 dollars, although that would include a hose and other
    attachments. A set of those sells for 10 to 15 dollars.

    So I'm doing well.

    I alswo bought at the junk yard two gas powered Homelite weed wackers
    for 7 dollars, figruing I could combine them to make one good one.
    Failed to notice that neither had a carburetor. I'm not sure what I'm
    going to do but I'm still ahead of the game.

    Thanks for the help.

    Meirman

    If emailing, please let me know whether
    or not you are posting the same letter.
    Change domain to erols.com, if necessary.
     
  6. NSM

    NSM Guest

    | I almost can't believe it, but after 35 years, I still get confused
    | about positive and negative. Sorry to bother you, but I just can't
    | remember.
    |
    | I'm replacing a bridge rectifier with 4 separate diodes, and I know
    | where the negative should be. ...




    +-+-- Pos out
    A A
    AC in -+ |
    AC in -(-+
    A A
    +-+-- Neg out

    Created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de)
     
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