DC Adapter question

Discussion in 'Computer Information' started by Ann-Marie, Jun 7, 2005.

  1. The 1 volt is generally true, but...

    Many electronics devices (two that I know positively fit this
    description are the Linksys WRT54G(S) series of wireless routers
    and the USR Courier series of modems) use a switching power
    supply internally. They aren't particular about the voltage fed
    to them. A WRT54G router will work well on any voltage from
    about 4 V to at least 20 V. A USR Courier will work at least
    with supplies from 9 V to 24 V.
    Doesn't necessarily help. With above two examples, a higher
    voltage will cause less current to flow. Ohm's Law suggest that
    if the voltage goes up the current necessarily goes up. But
    these devices are not simple resistors, and don't act like
    resistors. Other devices do though...

    The problem is that while what you've said is often right,
    sometimes it isn't. There's no substitute for an experienced
    eye when it comes to making judgement calls like selection of
    non-approved replacement parts. And it's always a crap shoot.
    And monster PC's! :)
    Floyd L. Davidson, Jun 8, 2005
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  2. Not really. If the voltage significantly changes then it isn't 'regulated'.
    That's what the word means in this context.
    There are lots of 'em, even in the traditional 'wall wort' form factor.
    Even more common in the brick form factor.

    A regulated wall wort in the power range being discussed would likely be a
    switcher rather than linear.

    I don't feel like bringing the network down to put a meter to it but I'd
    bet the 5V 2.5A wall wort to my D-link 614+ is a switcher because I don't
    see any way a 12.5VA transformer could fit in the 1.75x2.25x1 inch case,
    plus there's no weight to it, and the model number, SMP-xxxxx, looks
    suspiciously like an engineer's "Switch Mode Power" supply acronym.
    David Maynard, Jun 8, 2005
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  3. Ann-Marie

    Phil Weldon Guest

    'JANA' wrote: "The router draw the current that is correct."

    Correct, given everything is working properly.

    'JANA' wrote: "If you were to read up on ohm's law and understand it, you
    would understand the answer to this."

    Well, no, Ohm's law is not sufficient; the circuits involved are AC
    circuits, involving inductance, capacitance, resistance, inrush current, and
    power factors.

    'JANA' wrote: "A simple explanation, is that your AC outlet in the average
    home (In North America) can supply 15 Amps at 120 Volts."

    Well no, most wall sockets in USA buildings, if to electrical construction
    codes are on circuits breakered at 20 Amperes.

    'JANA' wrote: "Very few of your devices use more than 1 or 2 Amps." and
    "Very few of your devices use more than 1 or 2 Amps. The only exceptions are
    the air conditioner, toaster, microwave oven, and the electric kettle, just
    to mention a few."

    Fuzzy; most devices DO use more than one or two Amperes. The list of
    exceptions to a '1 or 2 Amps' limit is MUCH longer than the list of the
    devices below that limit. Other than small and florescent lamps, small
    radios, and wall warts, what's left under '1 or 2 Amps'?

    There are a number of non obvious differences between UK electrical codes,
    practices, and specifications and USA codes, practices, and specifications.
    Some of them are not obvious.

    1. It's not just the household voltages that are different, the AC
    frequency is 50Hz rather than 60Hz.
    2. AC circuits in the walls are wired as a loop rather than a line or tree.
    3. AC power cords tend to have a fuse in the plug.
    4. Color codes for AC wiring are NOT Black/White/Green.
    5. AC contacts (plugs and sockets) tend to be much heavier duty.

    The above and other points need to be considered when moving UK devices to
    the USA.

    'JANA' wrote
    Phil Weldon, Jun 8, 2005
  4. Yes *really*. "Regulation" is not specific enough. Some of
    regulators are better than others. Just saying "regulated"
    means zilch. And just saying the voltage changes means just
    about as much! How well regulated can be specified, and how
    much voltage changes can too.
    They are *rare* in the wall wort form, despite you knowing of an
    exception. The vast majority of wall worts that readers of this
    thread will ever see are *not* regulated.
    Typically that isn't done. The switcher is inside the
    equipment, and the wall wort amounts to little more than a
    transformer with a diode bridge, and might even have a

    It's good engineering practice, as it allows a variety of
    "power supplies" to be used. Personally, I don't see why
    anyone specifies a DC power supply anyway! They should move
    the rectifier and capacitor the equipment, which allows the
    wall wort to be AC or DC, and if DC it can be any polarity.
    That's nice flexibility.
    However, the fact that one such unit exists doesn't make it
    common, nor does it mean using it as a general example to
    describe the functionality of wall worts is a good idea.

    My point was that your comments were too narrowly focused on
    specific equipment that did not represent a broad enough view of
    what the OP, or others reading this thread via google searches
    next year, might be actually seeing.
    Floyd L. Davidson, Jun 8, 2005
  5. Ann-Marie

    McSpreader Guest

    1) Get a DC adapter that is specifed to deliver:
    a) 7.5V DC.
    b) not less than 1500ma.

    2) Check the DC supply plug for correct fit in the socket

    3) Check the DC plug for compatible polarity.

    4) Ignore the technomasturbatory responses in this thread.
    McSpreader, Jun 9, 2005
  6. Ann-Marie

    Phil Weldon Guest

    Exactly how not to make a first post to a group; and got the cart before the
    horse too!

    Phil Weldon
    Phil Weldon, Jun 9, 2005
  7. Ann-Marie

    Dave Guest

    You must keep the voltages the same but you can go higher on the current,
    not lower. So if the device says 7.5V at 1500mA then you must get one with
    7.5V and at least 1500mA. The 1700mA one will be fine.

    If you use a plug pack with less than 1500mA then you risk burning out the
    supply and/or the device which could lead to a fire.

    Of course some laptops can use a range of voltages but that would be stated
    on the device.

    Dave, Jun 9, 2005
  8. No, 'really'.
    Yes, it 'can be specified' but we're not talking about the Vcore regulator
    to a processor. We're talking about a wall wort and it's nonsense to
    contemplate an 'unregulated' regulated wall wort.

    We could also discuss how much ripple the unregulated wall wort is
    specified to put out at the specified current because there's the potential
    for a heck of a lot more variance in that than there is in the typical
    regulated wall wort.
    First you claimed you hadn't ever seen any, implying they don't exist, and
    now you want to argue 'percentages'.

    Perhaps I missed it but I don't recall it being said that the 'ac adapter'
    in question was even a 'wall wort'.

    Here's the package outline for Power Stream's selection in 15 watt wall
    wort switchers in both end and side mount plug, plus brick.


    And the specs for them: http://www.powerstream.com/Zdraw.htm
    That's certainly one way to do it. It's also not unusual to put a small
    switcher in the wall wort because, as the power levels go up, it's plain
    cheaper than a transformer. It's also more efficient with less weight, less
    bulk, and less heat.
    It may or may not be an advantage to allow a 'variety of power supplies'
    since a manufacturer usually knows what power supply they're providing.
    And some do it that way too. One could also argue that if you're moving
    everything else into the unit then you might as well put the transformer in
    it too.

    It depends on what one is trying to accomplish and what the device is for.
    If it's 'portable', as one example, then moving as much as possible into
    the external adapter removes bulk and weight from the portable device and,
    again using the portable example, there's little reason to carry around the
    transformer, rectifier, filter, and regulator when it's running on batteries.

    A fixed device, like a router, doesn't have that particular consideration
    but there are others, such as case size and internal heat dissipation, but
    I'm not going to debate the wisdom of D-Link design engineers as I don't
    know what design criteria they were handed.
    In the first place, I checked that particular unit because I just happen to
    have a D-Link (wireless/LAN) router and the device under question is, tada,
    a D-Link router, albeit a different model so one cannot assume it's the
    same. But it certainly shows that at least that one class of equipment, by
    the same manufacturer, employs a regulated wall wort.

    My D-Link 8 port switch uses a regulated adapter too, as do most notebooks
    in brick form, and I'm sure I could find more if I wandered outside the one

    Oh wait, the PDA is on a 5V 2A wall wort switcher (clearly labeled as such).
    Well pardon me for looking at a piece of equipment of the same type and
    manufacture as the one in question.
    You're arguing a straw man as no claim was made about 'how many' wall worts
    are regulated. Just that your absolute, 'they are all this way', statement
    that voltage will universally increase as load decreases is not true with a
    regulated power supply.

    And "others reading this thread via google searches next year" had better
    hear that regulated wall worts do, in fact, exist because replacing one
    with an unregulated wall wort isn't going to work worth spit.
    David Maynard, Jun 9, 2005
  9. Ann-Marie

    McSpreader Guest

    You've not been following this thread have you?
    McSpreader, Jun 9, 2005
  10. Ann-Marie

    Robert Baer Guest

    All unregulated "wall warts" have an excessively high output voltage,
    even at full rated load.
    The device that had a particular wall wart packaged with it must be
    designed to handle that excessive voltage with a good headroom, so use
    of a higher current-rated wall wart will make no practical difference.
    Robert Baer, Jun 9, 2005
  11. Ann-Marie

    Robert Baer Guest

    D A N G E R !
    Not all "US adaptors" are transformers.
    Robert Baer, Jun 9, 2005
  12. Ann-Marie

    Robert Baer Guest

    Within *one* volt???
    One is lucky to have an unregulated "wall wart" or wall transformer
    that is *less* than 20 percent high!
    Ten percent of that is due to typically high line voltage.

    Now, if the adaptor was a *regulated* unit, then the output voltage
    can be within 1% of specification.
    Robert Baer, Jun 9, 2005
  13. It's just good engineering.

    The rest of your article was mostly interesting opinion, but
    not significant either.
    Floyd L. Davidson, Jun 9, 2005
  14. (I'm not sure if you said what you meant, or if that is an
    editing error.) The rated voltage s essentially what it will
    put out when the load pulls the rated current. That's pretty
    much by definition, and isn't "excessively high output voltage".
    I'm assuming that previous paragraph must have been an editing
    error. If you mean that when the device is pulling less than
    full load, and therefore the voltage is higher than the stated
    voltage, the device must be designed to handle whatever that
    voltage is... yes, definitely. And in the case of most
    wireless units, which might have significant difference is
    current draw over very short periods of time, one of the reasons
    they use switching mode power supplies internally is to allow
    for a wide range of input voltage.

    In addition to handling the voltage swing from any given power
    source, it also allows them to buy whatever they can get the
    best deal on to ship as a power supply. It's very non-critical,
    and changing suppliers doesn't require any adaption of the device
    to match the new power supply.

    (One of the more hilarious examples of the above comes when
    someone gets a hold of an old USR Courier modem, sans power
    supply, and then posts a query to Usenet asking what kind of a
    power supply it requires. The answers list a confusing variety
    of voltages and current ratings! And the are *all* correct! USR
    has been shipping Courier modems for several years now, and
    they've used several significantly different power supplies.)
    Floyd L. Davidson, Jun 9, 2005
  15. Now I see what you were referring to in the other article, where
    you described it as "excessively high output voltage".

    Look at it this way... AC power in the US is "118 VAC", but that
    is a nominal voltage. It can be anything from 109 to 125 volts.

    So an unregulated power supply rated at 7.5 V might well interpret
    that as 7.5 V when the AC is 109 VAC. The output at 118 VAC would
    be 8.1 V. The output at 125 VAC would be 8.6 V.

    That's *15%* high just due to line voltage! Then, if they add
    on an extra 10% to avoid brownouts when the load hits momentary
    peaks of say 25% over the listed constant load rating...

    You've got a very good point about voltages!

    And can be 20% high, or even more, with little or no load.

    "Regulated" is a very loosely defined term... :)
    Floyd L. Davidson, Jun 9, 2005
  16. Speaking of 'unregulated' regulated wall worts isn't good english, logic,
    engineering, or anything else, except maybe humor.
    LOL. Listing specific wall wort switchers, including their rating, I happen
    to have in my possession and a manufacturer's site for the things, with
    full specifications and dimensions, is hardly "opinion."
    David Maynard, Jun 9, 2005
  17. That was *your* term, silly as it is.
    Floyd L. Davidson, Jun 9, 2005
  18. It is an accurate 'silliness' of your contention that a regulated supply
    may have significant voltage rise with a lower load than it's 'rating'
    (your original, and correct, warning about unregulated supplies that you
    clung to when I brought up regulated wall worts).

    But the whole point to "regulation" is to prevent precisely what you argue
    can take place so it would have to be 'unregulated' for your caution to be
    true, which would make it an 'unregulated' regulated wall wort, silly as it is.

    I really have no idea why you decided to turn a simple matter of regulated
    wall worts into a mash of mumbo jumbo. Say someone wants to replace a dead
    5V 2A SMP wall wort. What the hell do you suggest they get?
    David Maynard, Jun 9, 2005
  19. The DSL-604+ is an excellent product, although it's now at 'end of
    life'. I have one and have installed many more - very reliable, and one
    of D-Link's better products.

    Like most 'all-in-one' devices, it is (was?) not sold in the US. But
    strangely, I have a copy of apparently US-specific firmware stored away
    in a safe place, b3t14usa. So it's a lot earlier than the current UK
    firmware, b3t41uk. Anyway, I digress...

    The DSL-604+ *is* sold in Canada and can be found on the D-Link CA
    website here:
    It's currently distributed by Telus as part of their Home Networking

    Not only do I have a UK-spec model, but also a Canadian-spec model
    which I acquired from a customer who did what you have done - took his
    router with him. However, the firmware is Telus-specific and I'm unable
    to set it up for UK operation, and can't load the UK-spec firmware
    because it's a different hardware revision level. But I digress

    I have here in my hand a N. American spec external power supply for the
    DSL-604+ as supplied by D-Link CA. The details on the label say:
    Input: 120V AC 60Hz 20W
    Output: 7.5V DC 1.5A

    1. You could try D-Link CA and see if their spares dept (?) can ship
    one to you

    2. Let's do a swap. I'll send you mine if you send me yours. It's quite
    heavy (heavier than the UK equivalent) but I can ship it airmail small
    packet for around £6, and it'll be with you in say 3 days

    If you're interested, email me off list to arrange. Find my email
    address below. I'll also copy this to you by email (assuming the
    address in the header is valid) just in case you don't see this post.

    1. I'm sure the DSL-604+ will work just fine in the US with UK
    firmware, since it's set to autohandshake with the exchange / central
    office and will settle on the correct US comms standard (ANSI T1.413
    issue 2) rather than that used in the UK (ITU-T G.992.1).

    2. As someone else has said, don't use radio channels 12-13 as they are
    outside the frequency band allowed by the FCC.

    3. The DSL-604+ is/was one of the few such devices actually made by D-
    Link, or more specifically by their OEM/ODM division. This has now been
    spun off into a separate company, Alpha Networks

    4. If anyone knows the console password for the Telus-specific firmware
    for the DSL-604+ Rev B, please let me know. This is the password
    required to login either at the console port or via telnet. Hint: it's
    *not* admin/telus.

    5. I know a great deal about the DSL-604+ - but not the console
    password for the Telus-specific firmware. Anyone?

    Hope this helps


    Richard Perkin
    To email me, change the AT in the address below

    It's is not, it isn't ain't, and it's it's, not its, if you mean it
    is. If you don't, it's its. Then too, it's hers. It isn't her's.
    It isn't our's either. It's ours, and likewise yours and theirs.
    -- Oxford University Press, Edpress News
    Richard Perkin, Jun 9, 2005
  20. Wheee... This is fun. Permit me to throw in a few details.

    1. A problem with undersized wall warts is ripple. The smaller
    current handling xformer power supplies will tend to have undesized
    filter capacitors. Running at full load, the 60 or 120Hz ripple
    voltage can really screw up a 3 terminal regulator found in most
    bottom of the line wireless hardware.

    A rough approximation is:
    C = I / (120 * V)
    C = Cazapitance in Farads
    I = Load current in Amps
    V = Peak to peak ripple current desired in volts.
    So, for this device, I would probably want less than 50mv of ripple at
    1.6A load. Pluging:
    C = 1.6 / (120 * .05) = 267uF
    I've found some of the "replacement" power supplies to have very small
    (47uf) cazapitors and sometimes with a very marginal voltage rating.

    2. The maximum rating of these wall warts is often based upon self
    heating. That's caused by the xformer cores saturating. It's also a
    great way to get some free voltage regulation if you don't care about
    efficiency. Before the xformer gets too hot, the input/output voltage
    curve will tend to flatten somewhat. Some manufacturers take
    advantage of this effect by intentionally using undersized xformers
    and hopeing that the whole mess doesn't burn down the customers house.
    It usually doesn't but it does eventually cook the cheapo phenolic
    circuit board, diodes, and cazapitor inside the wall wart.

    3. The Dlink DSL-604+ wireless ADSL modem has apparently been FCC
    type accepted. However, my attempts to use the FCCID search
    abomination to find it by model number was unsuccessful. Duz anyone
    have the FCCID number for the DSL-604+? With that, I could lookup the
    type of power supply they use and see if it requires regulation.

    4. DLink has been using high efficient switching mode power supplies
    for quiet a while. They draw no power with no load. They are
    smaller, lighter, far more efficient, offer regulated voltage output,
    and have short circuit protection. They also generate lots of RFI
    which drives the hams nuts. I couldn't find a photo of the DSL-604+
    wall wart sold in UK. If it's a switcher, it should probably be
    replaced with a switcher as the DSL-604+ may rely on the added voltage
    regulation of the power supply. Difficult to tell without a look

    5. The voltage and current ratings are at "nominal" input voltage.
    For the US, that means 115VAC. Normal excursions are 105 to 125VAC
    input. For the 7.5VDC output, that's 6.8 to 8.2VDC. Neither extreme
    will cause a cheap 3 terminal 5VDC regulator with a 1.6VDC dropout
    voltage to stop working. LDO regulators are even less of a problem.
    Jeff Liebermann, Jun 9, 2005
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