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-48V DC vs. 48V DC vs. +48V DC

Discussion in 'Electronic Basics' started by Caiser, Oct 11, 2005.

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  1. Caiser

    Caiser Guest

  2. Randy Day

    Randy Day Guest

    I think the titles are a not-so-good way to group
    the supplies for their catalog software.

    They have different rated capacities in amperes, one
    has a 3.3v output, the three have different dimensions
    (L/W/H) and mounting hardware. One's for PS/2 pc's,
    one's ATX, and one seems to be a generic supply.
  3. Caiser

    Caiser Guest

    I know that all 3 of these power supplies are differrent but I am look
    more specifically at the input voltage, what is the difference between
    -48V DC, +48V, and 48VDC?


  5. Anytime you have a signed voltage it implies that there is a referance
    to some ground point. So -48VDC implies that you need to have the (+)
    side of your input voltage tied to ground (or there is an internal
    connection of the (+) to ground).

    By the same token, +48 would indicate that the (-) side of your input
    supply should be at ground (or perhaps there is an internal connection
    of the (-) to ground).

    It then follows that the unsigned 48VDC input has no particular
    preferance for which end is grounded.
  6. Kitchen Man

    Kitchen Man Guest

    The chassis reference is the most likely reason for the input polarity
    designation. Usually, with no sign given, the assumption is a
    negative chassis reference, or "+" voltage. The reason for indicating
    a difference is in application; if you are working comm gear,
    typically with a -48V power source, and you connect a +48V input
    supply (observing correct polarity), everything will be fine until you
    mount the +48V supply to a rack that is referenced to the other
    equipment. Now you've shorted out the facility power supply, with
    both the "+" and "-" output terminals connected to the ground
  7. Jasen Betts

    Jasen Betts Guest

    probably which side of the output is connected to ground.

  8. Rich Grise

    Rich Grise Guest

    Input, which you'd have seen if you'd looked at the links.

    Probably the first one is to run off the Telco batteries,
    which are positive ground because of the electrolysis problem
    with buried cables.

    And frankly, it looks like the other two don't care, since
    they're open frame - the difference between the second and
    third is only in the nomenclature, because the spec is the

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