DC Adapter question

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 capacitor.

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.

The router will draw the current that is correct. You need to match the voltage to within about 1 Volt. The rating of the adaptor is the maximum safe load it can handle. You can use the 1700 ma one, as long as the voltage is correct.

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

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

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.

'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.

"Ann-Marie" wrote in news:sMkpe.2181$ snipped-for-privacy@newssvr17.news.prodigy.com:

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.

It's just good engineering.

The rest of your article was mostly interesting opinion, but not significant either.

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:

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 room.

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.

(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.)

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

Phil Weldon

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... :-)

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

That was *your* term, silly as it is.

"Phil Weldon" wrote in news:fpOpe.1430$ snipped-for-privacy@newsread2.news.atl.earthlink.net:

You've not been following this thread have you?

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."

The term was yours, and it is silly (and all the other adjectives you used to describe it). Which is why *I* didn't use it.

If you think so, you'd better take a closer look at real life regulators!

Sometimes the whole point of a "regulator" is ripple reduction at 60 Hz and it's harmonics. Sometimes the whole point of a "regulator" is to provide regulation within a very minimal range.

And sometimes "regulation" means within 20%, sometimes 10% and sometimes 0.1%.

I suppose I could go on with a longer list of ambiguities, but those are all well known and should be enough to demonstrate that your statement about "regulation" just doesn't have a lot of meaning. The point is that not all regulated power supplies maintain the same voltage with no load, and that some regulated power supplies do not regulate well except within a specified load range. Regardless, your original statement tried to generalize something specific that generally may not be true.

I'm sorry you don't understand the technical aspects, but that does suggest you perhaps shouldn't try to post technical answers.

A live "5V 2A SMP wall wort".

Whatever, this conversation is finished. You can have the last words. Just do try for something a little better than unregulated regulated power, eh?

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.

D A N G E R ! Not all "US adaptors" are transformers. *WARNING*

Within *one* volt??? Garbage! 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.

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) where: 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.

1. 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.
2. 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.
3. 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 inside.
4. 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.