12dc > 240ac inverter; input polarity not clear

Discussion in 'General Electronics Chat' started by arfa2, Sep 5, 2016.

  1. arfa2

    Thread Starter New Member

    Sep 5, 2016
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    I recently inherited a 12Vdc > 240Vac inverter. A "Dick Smith M5100 150W". I have googled for a wiring diagram - or any info but nothing of use was forthcoming.
    It looks like it has hardly been used so I presume it works. BUT... there are no markings for DC input. There are no unit terminals - just a raw cable exiting and it has been cut and ends stripped - presumable to wrap directly to the battery. I presume there may have been battery post clips at one stage. I read one post on the site where reversed polarity popped the works so I am cautious.
    I have set a photo below in the hope that someone may conclude the obvious. I live remote so don't get to town often.
    With a 50/50 shot I would guess that the wire with the writing, feeding to the transformer? would be positive.

    Any thoughts? - on the image below or suggestions on how I might determine which wire is which.
    [​IMG]
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,030
    1,622
    Just follow the polarity markings on the input side capacitors back to which wire they are connected with.
     
  3. arfa2

    Thread Starter New Member

    Sep 5, 2016
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    Many thanks for the speedy reply tcmtech.
    I am very limited in tech knowledge. Bear with me if you can.

    "input side capacitors back to which wire they are connected"
    are they the two 'big round things' to the left of the transformer?
    will I be able to see the markings on this topside? or, will I need to fully open the unit to view the underside of the board?
    I presume the capacitor will have a visible '+' or '--'

    sorry if this is too newbie for this forum but, as I mentioned, access to a store tech person is limited.
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,030
    1,622
    Yep it's the two black cans. They have a white line down one side with the (-) sign on it.

    That's obviously the negative terminal and thusly the bigger input wire that connects to that same circuit trace is the negative power line.
     
  5. arfa2

    Thread Starter New Member

    Sep 5, 2016
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    That's great.
    The unit is back in my cabin and I am about to head back there so will see what I can see and report back tomorrow.

    thanks a bunch.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    The polarity markings on those two caps can be seen in the photo. See the whitish lines (bars?) on the black backgrounds? Those are both the negative sides. They both face the wire without printing on it (in the photo, anyway) that is farther away from the transformer. That wire is likely negative. But go ahead and verify.
     
  7. arfa2

    Thread Starter New Member

    Sep 5, 2016
    4
    0
    Yes, right on the money.
    I had to remove the board to clearly view the circuitry but it was easy enough to see.

    Many thanks for your very helpful directions.
     
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