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Wall Wart Woes!

Discussion in 'Electronic Design' started by Martin Brown, Feb 20, 2012.

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  1. Martin Brown

    Martin Brown Guest

    I wonder how many of us have old modems/WiFis/Routers salted away in a
    dark cupboard waiting for the day when they might be needed again for
    something? (usually helping a charity with their IT needs)

    The main annoyance is that the wall warts and even laptop PC supplies of
    old span a crazy range of random voltages and both polarities. And the
    PSU often dies or simply gets lost leaving the unit orphaned.

    That isn't too much of a problem since modern switched mode supplies and
    fit anything connectors are easy enough to come by. The really annoying
    thing in recycling kit for a charity where the original PSU is lost is
    that in most cases neither the manual nor the unit itself states whether
    the power connector is positive or negative centre pin. The lost PSU of
    course displays which voltage, current and polarity it outputs but the
    unit requiring power very often does not.

    Now you could take it apart, but more often just play Russian roulette
    and see if the LEDs light. Why can't manufacturers label the connector
    with (+)- or (-)+ nnV/mmA? I am fed up with just seeing "POWER".

    That label tells me nothing I can't already guess from the type of
    connector - what I really want to know is what voltage and polarity!

    Does anyone else find this annoying?
  2. PeterD

    PeterD Guest

    I know this is high level rocket science, but...

    1. The label on the unit tells the voltage. Always.

    2. The polarity can be determined with a visual inspection of the board
    at the connector, they will have at least one filter capacitor, with a
    marked plus lead.
  3. WoolyBully

    WoolyBully Guest

    The polarity of the connector is also almost always on the AC powered
    product ID label as well. OR it can be ID'd from the cord feeding the
    plug sometimes too. The 'icon' on the device being powered sometimes
    shows the polarity 'desired' by it as well. Look closely at the logo at
    the power pin, if there is one.

    The standard is typically "center positive" because the connector
    design is usually such that the barrel (outer) connects first. Or for
    whatever reason, it has been pretty much the de-facto method.

    There are, however "center negative" versions as well. So much for
    adopting and maintaining standards. Maybe we should ring the necks of
    all the dopes who stubbornly did it "their way" anyway.

    I have also used in a design, types which have a threaded ferrule on
    them and actually attach to the device the get plugged into. I would want
    that exposed ferrule to be chassis, which is usually negative.
  4. Don Y

    Don Y Guest

    Hi Martin,

    I volunteer at a non-profit that actually *receives* such kit for
    recycling. If you think its bad trying to chase down *your* wall wart
    for *your* piece of kit, imagine the problem when donors drop off
    random bits of kit with the wall warts in a knotted tangle -- which
    often doesn't include *the* wall wart for the item of interest!

    (We have, literally, garbage *cans* full of wall warts whose mates
    are unknown)

    Some vendors will mark the product with the voltage and polarity of
    the expected power source. Then, it's "just" a matter of finding
    the appropriate barrel diameter and center post diameter to "fit".
    One gripe *I* have is that the standard scheme for indicating polarity
    doesn't fare well as it is scaled. Something like:

    + ----* )---- -

    where the ")" signifying the barrel contact actually wraps around the
    "*" signifying the center post. Ink bleed at small scales often turns
    this into a guessing game: "is that a '-' or a '+'? Is the line
    from that +/- symbol going to the center *pin*? Or, the enclosing

    Why not a simple circle with a sign inside? Takes LESS space on the
    label (so it could be printed at a larger scale) and removes some of the

    Or, design devices that are tolerant of polarity reversals! (ideally,
    *functioning* with either polarity or at least not giving up the
    ghost with "reversed" polarity!)

    For my own, personal items, I label each wall wart with the name of
    its mate and write the power requirements on the mate with a "Sharpie"
    using the "circled sign" graphic I described accompanied by
    voltage and amperage. I have a *white* pen for those items
    that have black cases.
    A vendor once made the observation that center positive is common
    for US market while many other markets have center negative. I
    suspect that is *not* universally true (as I have encountered
    lots of kit with center negative).
    Let's see... how many souls currently on the planet?
  5. Pimpom

    Pimpom Guest

    I've just had a look at the two wallwart-powered ADSL modems on
    my desk, and though they both specify the required DC supply
    voltages, neither one shows the polarity. They are neither
    moulded nor printed anywhere.

    A high majority of the devices I've worked with and on over the
    years use the outer ring as the positive contact, with the
    opposite polarization being occasional exceptions. I've always
    considered the more common practice illogical.
  6. Guest

    Mostly because the wall wart is used for everything the company makes and is
    usually an off-the-shelf item.
  7. David Lesher

    David Lesher Guest

  8. David Lesher

    David Lesher Guest

    Because K's builder bought the wallwarts from Delta or another wallwart
    supplier....and they charge real money for custom labels. Further,
    they also fit K950's, L111's and etc. What label should they pay Delta
    to use?
  9. David Lesher

    David Lesher Guest

    Because Linksys bought each version from a different supplier, I bet.
  10. Don Y

    Don Y Guest

    Hi David,

    And what happens when the wall wart gets misplaced?

    Wall wart (applies to bricks as well) *and* device
    need to clearly indicate their power requirements.
    ON THE DEVICES (since you can't expect a user to
    hold onto any printed documentation that came with
    the original product -- nor can you rely on vendors
    to maintain this information on web sites, help desks,

    Ink is cheap (or, raised lettering on a mold).

    (though this still ignores the issue of protecting
    that device from "inappropriate" power adapter choices
    on the part of the user!)
  11. Baron

    Baron Guest

    WoolyBully Inscribed thus:
    What about the ones that actually require an AC supply. Granted you are
    unlikely to cause any damage irrespective of the polarity of a DC
  12. David Lesher

    David Lesher Guest

    The EU, tired of tens of millions of junked smartphone chargers
    per year, mandated 5VDC/microUSB. The phone builders balked at
    first, then grokked then no longer need to ship one with each

    Apple, of course, is upset. They make big money selling
    replacement chargers.
  13. WoolyBully

    WoolyBully Guest

    I find it funny that a huge number of AC fed power supplies (only the
    switchers) will work, no problem at all, if fed with DC.

    Since there is no transformer, no cycling is needed.

    One cannot do that with a linear, transformer front ended power supply.
  14. HectorZeroni

    HectorZeroni Guest

    Maybe because they are owned by, and their designs are engineered by
    Cisco now.
  15. Guest

    No, because the droid in shipping reaches in the bin and pulls one to stick in
    the kit. There are likely four vendors' wall warts in the bin, which is used
    for 999 different kits.
    We'd mark the case with the "universal symbol" (concentric circles, with a
    line going to a "+" for CPP) and the voltage. It costs a little. I don't
    understand why there would ever be CPN, but that's just me.
    You think people are going to read a silly sticker before plugging something
    in? If it fits, it's going to be tried. I tried to code the voltage and
    current into the connectors (center pin diameter and length) but it cost quite
    a bit, in both $$ and aggravation, to do it and it didn't always work.
  16. Guest

    I think that's a UL requirement, but maybe not for really low power devices.
    I tried to do that with a TVS and polyfuse. Low voltages were still a
    problem, though.
  17. Martin Brown

    Martin Brown Guest

    Sometimes you can recognise the maker even when it *is* badged. I don't
    mind so much that the wart doesn't say which product it belongs with so
    long as both PSU and product both state their ratings and polarity.

    I find a dab of coloured paint on the plug and socket helps avoid
    embarrassing smoke emissions where different scanners/routers have
    identical connectors but significantly different voltage requirements.
    Problem is that the same unit likely powers a dozen different products.

    What I want is the product having a case moulding that includes the
    power polarity, voltage and current requirements of the product. This
    labelling is mandatory for mains powered equipment, but apparently once
    you stick a wall wart in the way you can just put a 3.5mm socket
    labelled "POWER" on the outside and be done with it.

    Mass production techniques don't cost more for a few extra characters on
    the injection moulded back panel, nor would it hurt to include these
    details in the manual tech ref pages! Virtual ink costs nothing.

    It seems most engineers agree with me so how do we get the halfwitted
    MBAs to make the change? I guess they see customers blowing things up
    due to badly designed power connectors as a way to increase sales.
    EU inspired thing to prevent the insane proliferation of utterly
    incompatible mobile phone charges using ever more exotic shaped
    connectors but almost all about the same voltage and power.
  18. mike

    mike Guest

    You should get out more.
    Always is an often misused word.
    If there's a connector accessible, that often connects to ground.
    Then you can measure from that connector to the power socket to determine
    the ground connection. The other one is often positive.
  19. Don Y

    Don Y Guest

    Hi Peter,

    So, we're supposed to disassemble each such device (think: flimsy
    snap-together construction... if not *gasp* solvent welded!) and
    go on a reverse-engineering mission?

    You can sort out polarity. And, you can put an upper limit on the
    *voltage* (not to exceed the lowest WVDC of the caps on that line).
    But, no idea as to current requirements.

    All this work just so a vendor can AVOID marking his product clearly?
    Hint to manufacturers: make your corporate logo smaller if you don't
    have room for this information (<gasp>)
  20. WoolyBully

    WoolyBully Guest

    Especially in this fucked up group.
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