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DC Adapter question



 
 
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  #21  
Old June 8th 05, 08:39 PM
Floyd L. Davidson
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David Maynard wrote:
Floyd L. Davidson wrote:

Robert Baer wrote:

A supply could be rated at 1000A and work no differntly than
one rated at 1700mA.
It is the *voltage* rating that one must be cautious about.

Almost, but not quite. If a DC supply is significantly under
loaded,
the voltage will rise.


That's true if it's unregulated but the voltage change with a
regulated supply is negligible.


That would depend on the regulation, but regardless... I've
never seen a regulated wall wort.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #22  
Old June 8th 05, 08:52 PM
Floyd L. Davidson
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"JANA" wrote:
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.


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.

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


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.

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.


And monster PC's! :-)

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #23  
Old June 8th 05, 09:27 PM
David Maynard
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Floyd L. Davidson wrote:

David Maynard wrote:

Floyd L. Davidson wrote:


Robert Baer wrote:


A supply could be rated at 1000A and work no differntly than
one rated at 1700mA.
It is the *voltage* rating that one must be cautious about.

Almost, but not quite. If a DC supply is significantly under
loaded,
the voltage will rise.


That's true if it's unregulated but the voltage change with a
regulated supply is negligible.



That would depend on the regulation,


Not really. If the voltage significantly changes then it isn't 'regulated'.
That's what the word means in this context.

but regardless... I've
never seen a regulated wall wort.


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.



  #24  
Old June 8th 05, 11:11 PM
Phil Weldon
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'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
"JANA" wrote in message
...
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.

--

JANA
_____


"Ann-Marie" wrote in message
...
Hi,
I just moved from the UK to the US. I brought my Wireless access
point/router with me, but I need to get a new DC adapter for it so that it
works on the 110V supply here.

It says on my UK adapter that the output is: 7.5V DC 1500mA 11.25VA

Every universal adapter I find that has 7.5 as an option, seems to have a
current rating of either below, or above the 1500mA I need. They are
usually
either about 1000mA, or 1700mA etc.

Does anyone know if this is a required rating, or if it will automatically
only take the current required, as long as it's set to 7.5V ?

For example, if I get the one with only 1000mA rating, will it not work?
If
I get the 1700mA one, will it be too much and blow the wireless access
point?

Thanks for any help,
Daniel





  #25  
Old June 8th 05, 11:23 PM
Floyd L. Davidson
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Default

David Maynard wrote:
Floyd L. Davidson wrote:

That's true if it's unregulated but the voltage change with a
regulated supply is negligible.

That would depend on the regulation,


Not really. If the voltage significantly changes then it isn't
'regulated'. That's what the word means in this context.


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.

but regardless... I've
never seen a regulated wall wort.


There are lots of 'em, even in the traditional 'wall wort' form
factor. Even more common in the brick form factor.


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.

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


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.

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.


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 http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #26  
Old June 9th 05, 12:51 AM
McSpreader
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"Ann-Marie" wrote in
:

7.5V DC 1500mA


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.
  #27  
Old June 9th 05, 04:08 AM
Phil Weldon
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Exactly how not to make a first post to a group; and got the cart before the
horse too!

Phil Weldon

"McSpreader" wrote in message
...
...



  #28  
Old June 9th 05, 05:41 AM
Dave
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"Ann-Marie" wrote in message
m...
Hi,
It's a D-link DSL-604+, it has built in modem, router, switch, WAP, so I
guess thats why it takes quite a lot of power.

I looked in the manual, and it says the power consumption is 12W max,
which, I worked out to be 1.6A at 7.5V - would that be right?

If I get this 1700mA adapter, and run it at 7.5V, is there a risk of fire
or anything? or is that only if I got a lower rated one.

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



  #29  
Old June 9th 05, 08:02 AM
David Maynard
external usenet poster
 
Posts: n/a
Default

Floyd L. Davidson wrote:
David Maynard wrote:

Floyd L. Davidson wrote:

That's true if it's unregulated but the voltage change with a
regulated supply is negligible.

That would depend on the regulation,


Not really. If the voltage significantly changes then it isn't
'regulated'. That's what the word means in this context.



Yes *really*.


No, '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.


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.

but regardless... I've
never seen a regulated wall wort.


There are lots of 'em, even in the traditional 'wall wort' form
factor. Even more common in the brick form factor.



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.


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.

http://www.powerstream.com/Zdraw.htm

And the specs for them: http://www.powerstream.com/Zdraw.htm

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



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.


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's good engineering practice, as it allows a variety of
"power supplies" to be used.


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.

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.


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.

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.



However, the fact that one such unit exists doesn't make it
common,


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).

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


Well pardon me for looking at a piece of equipment of the same type and
manufacture as the one in question.

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.


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.



  #30  
Old June 9th 05, 09:41 AM
McSpreader
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"Phil Weldon" wrote in
k.net:

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

Phil Weldon

"McSpreader" wrote in message
...
...




You've not been following this thread have you?
 




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