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9 + 9 =18?

Discussion in 'Electrical Engineering' started by Virginia Belle, Nov 19, 2003.

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  1. I Know that this is a dumb question but, I am curious anyway.

    Lets just say that I need an 18 volt DC power source and that the source
    has to come from one of those transformers? that plug into the wall and
    change AC to DC.

    What if I only have two of those transformer devices that are 9 Volts
    DC each.

    Now, If I cut the insulation off of the ends of both of those
    transformers, take the two wire ends from each and twist the 4 ends
    together to make two again, plug them in, will THAT make me the 18 volts
    that I need?

    9 + 9 makes 18 doesn't it?

    PLEASE tell me that I have made SOME sense here?

    Thank You
  2. EEng

    EEng Guest

    I won't go into the right or wrong of it, but to answer your

    Strip the insulation from each of the four wires. Twist together the
    negative of one adapter to the positive of the other adapter. This
    leaves you two open wires, one positive, one negative, and you now
    have 18V.
  3. John Gilmer

    John Gilmer Guest

    I have yet to see any wall wart with a ground connection.

    If your "wall warts" are designed to replace 9 volt bateries, you can cut
    the part that go to the appliance in half and connect ONLY the male of one
    to the female of the other. The unused male and female will have your 18
  4. It is also a good idea to use identical wallwarts. If you use different
    ones, imbalances can occur, especially if they are poorly regulated
    (like most are...)

  5. Guest

    It's not a dumb question at all. 9 volt wall warts
    deliver 9 volts *at their rated current*. If you
    run them at a different current, the voltage could
    be considerably higher or lower.

    If the two wall warts have identical current specs,
    you'll get 18 volts at the load for which the transformers
    are rated. The problem is that MOST wall warts are not
    regulated. That means that a wall wart rated 9 volts,
    100 mA may put out say 12 volts if it is connected to
    a load that draws 10 mA instead of 100 mA.

    The bottom line is this: when you connect the
    two wall warts in series and then connect the
    two remaining wires to the load, you may not get
    18 volts. You could get well above or well below
  6. DaveC

    DaveC Guest

  7. John G

    John G Guest

    She posted seperately to several newsgroups that I look at and as well as
    the usual many similar answers to the same question she got them in all
    sorts of variations in EACH newsgroup.
    What a waste of band width.
  8. John Gilmer

    John Gilmer Guest


    You are starting to sound like someone who looks under his bed before going
    to sleep.

    Actually most don't even have polarized plugs.
  9. John Gilmer

    John Gilmer Guest

    Sure. Putting two wall warts in series will come back to "bite you on your

    Get real!
  10. I don't think I've seen a US/Canadian one that's a true "wall wart",
    though the "brick" type, both linear and switching types, often do
    have the output grounded. If the AC plug has only two pins, there's
    nothing to worry about.

    Best regards,
    Spehro Pefhany
  11. As I pointed out in another newsgroup, what happens to the filter
    capacitor when one of the two accidentally gets unplugged and you have
    not added diodes across the outputs?

    Best regards,
    Spehro Pefhany
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