input 0.18A @ 220V output 1A @ 5V

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Man-wai Chang

I read these spec from an AC-to-DC adapter for a 4-port USB hub.

Does it sound weird? I meant the current... :)

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I read these spec from an AC-to-DC adapter for a 4-port USB hub.

Does it sound weird? I meant the current... :)
Click to expand...

Other than it being extremely inefficient, what are you concerned about?
 
I read these spec from an AC-to-DC adapter for a 4-port USB hub.
Other than it being extremely inefficient, what are you concerned about?
Click to expand...

I understand by definition it looks OK.

But how do u explain in electron level how 0.18A become 1A? :)

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Man-wai Chang said:
I understand by definition it looks OK.

But how do u explain in electron level how 0.18A become 1A? :)
Click to expand...

If you ignore the efficiency issue, "power is conserved".

If you want 5V at 1A on the output, and your source is 20V,
you'd expect 20V at 0.25A on the input side. The product of
V*I should be constant.

The power supply is not an ideal "transformation device". It is
not 100% efficient. So instead of putting in 20V at 0.25A
to make 5V at 1A, you might need 20V at 0.30A. The excess is
dissipated as heat, in things like power transistors, transformers
or diodes.

So when you use a very high voltage like 220V, you expect a
very low current number to go with it (the product of the two,
to give you 5 watts total).

*******

That still doesn't explain the above numbers though.
0.18A is too high.

First of all, what it said on the adapter was probably
something like this:

100-220V 0.18A

In other words, a "universal" adapter, capable of running
at two different line voltages. Simply change adapter
cords, to connect to a different kind of wall socket.

The 0.18A value is quoted at the *lowest* applied voltage, which
is 100V in this example. 100V * 0.18A = 18W.

Now, compare to the output of 5W. This is terrible efficiency.
And as a practical check, feel the outside of the adapter.
Does it feel like 13W is wasted as heat, ever ? Probably
not. It probably feels like it is running cooler than that.

Could we account for it a bit, by assuming a 0.7 power factor.
That probably wouldn't account for all the difference between
18W input and 5W output.

I can't adequately explain it. I've seen things like this
before, but have never investigated any further for an answer.
Obviously, they've measured some current, or they've attempted
to estimate the worst case current flow value. That's about
all I can suggest, it's an estimate that just never happens
in practice.

Maybe someone else has an idea where those imaginative
numbers come from.

Paul
 
The 0.18A value is quoted at the *lowest* applied voltage, which
is 100V in this example. 100V * 0.18A = 18W.

Now, compare to the output of 5W. This is terrible efficiency.
And as a practical check, feel the outside of the adapter.
Does it feel like 13W is wasted as heat, ever ? Probably
not. It probably feels like it is running cooler than that.
Click to expand...

It's not hot. But I have never pushed it to its limits.

It's actually the power supply for a 4-port USB hub. I don't know why
only a 1A power supply was bundled with it when you should need 500mA
times 4. :)

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Man-wai Chang said:
It's not hot. But I have never pushed it to its limits.

It's actually the power supply for a 4-port USB hub. I don't know why
only a 1A power supply was bundled with it when you should need 500mA
times 4. :)
Click to expand...

Yes, but how many customers would notice that ?

If the adapter is overloaded, it will shut off.

Paul
 
But I have never pushed it to its limits.

It's actually the power supply for a 4-port USB hub. I don't know why
only a 1A power supply was bundled with it when you should need 500mA
times 4. :)
Click to expand...

But, as you haven't, then the onus remains essentially yours. . .both
for having chosen an external powered port for selecting a particular
USB device(s) to premise reason, if then at what point reason is
exceeded by demand or expectation;- It's either of two prongs: a) when
you've got an error report in the operating system, or not, that b) a
fault condition occurs when exceeding specifications (2nd & 4th
passages respectively from wiki). . .

A bus-powered hub is a hub that draws all its power from the host
computer's USB interface. It does not need a separate power
connection. However, many devices require more power than this method
can provide, and will not work in this type of hub.

USB current (related to power) is allocated in units of 100 mA up to a
maximum total of 500 mA per port. Therefore a compliant bus powered
hub can have no more than four downstream ports and cannot offer more
than four 100 mA units of current in total to downstream devices
(since the hub needs one unit for itself). If a device requires more
units of current than the port it is plugged into can supply, the
operating system usually reports this to the user.

In contrast a self-powered hub is one that takes its power from an
external power supply unit and can therefore provide full power (up to
500 mA) to every port. Many hubs can operate as either bus powered or
self powered hubs.

However, there are many non-compliant hubs on the market which
announce themselves to the host as self-powered despite really being
bus-powered. Equally there are plenty of non-compliant devices that
use more than 100 mA without announcing this fact (or indeed sometimes
without identifying themselves as USB devices at all). These hubs and
devices do allow more flexibility in the use of power (in particular
many devices use far less than 100 mA and many USB ports can supply
more than 500 mA before going into overload shut-off) but they are
likely to make power problems harder to diagnose.

Some self-powered hubs do not supply enough power to drive a 500mA
load on every port. For example, many seven port hubs have a 1A power
supply, when in fact seven ports could draw a maximum of 7 x 0.5 =
3.5A, plus power for the hub itself. Designers assume the user will
most likely connect many low power devices and only one or two
requiring a full 500mA.
 
Man-wai Chang said:
I read these spec from an AC-to-DC adapter for a 4-port USB hub.

Does it sound weird? I meant the current... :)
Click to expand...

15W in (120VAC/sqrt2 = 85Vrms; 85Vrms * 0.18A = 15W)
5W out (5V + 1A = 5W)
10W loss (15W - 5W = 10W; transformer dissipates 10W)
33% efficiency (very poor)

What did you think was weird? That you got less power out then went in?
That's how this universe works (lookup "entropy"). Despite entropy (due
to inefficiency), there is generally a conservation of energy, so you
get [mostly] out what you put in. Ohm's Law can be rewritten as R = V*I
(power = voltage times amperes). If voltage goes down then current has
to go up for power to remain the same. Due to inefficiency (dissipated
as heat) in transferring power, the power output will be less. Read up
on Ohm's Law:

http://en.wikipedia.org/wiki/Ohms_law

Is your concern that this unit is highly inefficient? So maybe it's a
super cheapy design. Is your concern that there is only 1A available
for all 4 ports instead of .5A for each one for a total of 2A available
overall? Well, that would be poor design but there's lots of hardware
poorly designed.

Is this a secret 4-port USB hub? If not, why no URL link to it so
others can see what you are asking about?

In another of your posts, you said "explain in electron level how 0.18A
become 1A?". What? You've never heard of [step-down] transformers or
not a clue how they work? If so, start here:

http://en.wikipedia.org/wiki/Transformer
http://www.energyquest.ca.gov/how_it_works/transformer.html
http://sound.westhost.com/xfmr.htm
 
But, as you haven't, then the onus remains essentially yours. . .both
for having chosen an external powered port for selecting a particular
USB device(s) to premise reason, if then at what point reason is
exceeded by demand or expectation;- It's either of two prongs: a) when
you've got an error report in the operating system, or not, that b) a
fault condition occurs when exceeding specifications (2nd& 4th
passages respectively from wiki). . .
Click to expand...

The power supply was hidden in the package. How could I find out? By the
price alone? :)

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Thanks. I will do my homework first.

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The power supply was hidden in the package. How could I find out? By the
price alone? :)
Click to expand...

Was called for an issue once with a powered hub and printer on an
office machine. OS was reporting back an error, so I unplugged the
hub, figured a way to get around it, directly to connect the printer
and that fixed it. Doubt yours ran less than the only $1.99 four-port
hub I've owned, I gave away recently to a guy after helping him pick
out and setup a TASCAM multitrack recorder. Haven't really much
current needs for just a few simple USB devices I do have, pretty much
along standard to conveniences and plenty of ports on newer cases.
 
Franc said:
The mains voltage rating is in RMS.

So 120VAC = 120Vrms, not peak.
Click to expand...

Schwack (me slapping my forehead).

Oops, you're right. I'm too used to looking at oscilloscope traces so
when someone says X VAC then I too often automatically figure that's
peak to peak so I divide by .707 to get RMS (but then I'm also assuming
sinusoidal AC and not some stepped or oddball waveform). Like you say,
the peak-to-peak voltage for household is ±170VAC and that's 120VACrms.

22W in (120Vrms * .18A)
5W out (5V * 1A)
23% efficiency (not 33%)

That means efficiency is even worse. At 100% efficiency, the input
current should only be 42mA to produce 5W output, not the 180mA the OP
mentioned. So I suspect the input spec is for worst case or max safe
draw, not for typical draw. Also, since the output current is clamped
to protect the connected devices, you'll never get out the max power on
the output side so you won't know what is the real efficiency of the
converter.

Still is seems odd the max output is 1A instead of 2A when there are 4
USB ports and each one should provide .5A max. There are some hi-power
USB devices that won't work with just .25A, like an iPod or PDA. An
iPod takes 430mA (running or sleeping) to charge from a discharged
state. The Dell Axim x50 takes 840mA max when running to recharge (will
work on a 5V/500mA port but may drop voltage on other ports if connected
to a 5V/100mA port). It's charger auto-stops after 7 hours but with
only 250mA available on this USB hub's port then the user would have to
unplug and replug the charger to start another charging cycle.

So far, we don't know what USB hub the OP is asking about since no brand
and model has been supplied or a URL to the device if he's thinking
about getting it. I suspect the OP is in his scavenge mode again
digging through a drawer of miscellaneous parts and wondering if some
adapter he found is usable for some unidentified purpose.
 
Schwack (me slapping my forehead).

Oops, you're right. I'm too used to looking at oscilloscope traces so
when someone says X VAC then I too often automatically figure that's
peak to peak so I divide by .707 to get RMS (but then I'm also assuming
sinusoidal AC and not some stepped or oddball waveform). Like you say,
the peak-to-peak voltage for household is ±170VAC and that's 120VACrms.

22W in (120Vrms * .18A)
5W out (5V * 1A)
23% efficiency (not 33%)

That means efficiency is even worse. At 100% efficiency, the input
current should only be 42mA to produce 5W output, not the 180mA the OP
mentioned. So I suspect the input spec is for worst case or max safe
draw, not for typical draw. Also, since the output current is clamped
to protect the connected devices, you'll never get out the max power on
the output side so you won't know what is the real efficiency of the
converter.

Still is seems odd the max output is 1A instead of 2A when there are 4
USB ports and each one should provide .5A max. There are some hi-power
USB devices that won't work with just .25A, like an iPod or PDA. An
iPod takes 430mA (running or sleeping) to charge from a discharged
state. The Dell Axim x50 takes 840mA max when running to recharge (will
work on a 5V/500mA port but may drop voltage on other ports if connected
to a 5V/100mA port). It's charger auto-stops after 7 hours but with
only 250mA available on this USB hub's port then the user would have to
unplug and replug the charger to start another charging cycle.

So far, we don't know what USB hub the OP is asking about since no brand
and model has been supplied or a URL to the device if he's thinking
about getting it. I suspect the OP is in his scavenge mode again
digging through a drawer of miscellaneous parts and wondering if some
adapter he found is usable for some unidentified purpose.
Click to expand...

Is there any plausibility to the idea that the output rating listed is
per port?
 
What's the primary winding inductance figure when the secondary winding is
shorted ? Usually, those little transformers are design to whistand the
short circuit without burning hence fireproof. In such a case, the iron (and
copper) temp should below something like 60 °C.
That's been a long time I didn't design transformers and standards have
evolved a lot.
Please check Google on the topic.
 
TVeblen said:
Is there any plausibility to the idea that the output rating listed is
per port?
Click to expand...

USB is rated in "unit loads". 1 unit load is 100mA so 5 unit loads are
500mA. The max unit loads handled by a USB port is 5. I haven't heard
the USB specs got updated to handle more than 5 unit loads (500mA).

USB 3.0 changed the definition of "unit load" to 150mA, so 1 unit load
is 150mA. USB3 upped the unit load count to 6, so 6 max unit loads
would be 900mA (still not quite the 1000mA rating noted by the OP).

We still don't know anything about brand and model of the power adapter
queried by the OP or with what it was meant to be used. Could be they
put 1A simply because they didn't have room for 900mA or they are doing
the slipshod marketing crap of using a better "near value", like when
the marketing aholes decided they could make hard disks look bigger
using decimal byte values instead of binary-based values. Note that as
far as we know, the OP stated the spec for the adapter, not the USB hub
itself (which it appears the OP doesn't have). If it is rated at 1A
than that it's total max output. If it were used for a 2-port USB hub
then each port would have .5A (probably a bit less since the internal
circuitry consumes some power). If it is a 4-port USB hub as the OP
states than the max with 100% efficiency in the circuitry would be just
..25A per port. I doubt the rating printed on the power adapter reflects
anything about the rated output of each port on the separate USB hub
device. But then maybe the OP gave us the spec for the entire product
(adapter + hub) or he gave us what he saw printed on the adapter.
 
USB is rated in "unit loads". 1 unit load is 100mA so 5 unit loads are
500mA. The max unit loads handled by a USB port is 5. I haven't heard
the USB specs got updated to handle more than 5 unit loads (500mA).

USB 3.0 changed the definition of "unit load" to 150mA, so 1 unit load
is 150mA. USB3 upped the unit load count to 6, so 6 max unit loads
would be 900mA (still not quite the 1000mA rating noted by the OP).

We still don't know anything about brand and model of the power adapter
queried by the OP or with what it was meant to be used. Could be they
put 1A simply because they didn't have room for 900mA or they are doing
the slipshod marketing crap of using a better "near value", like when
the marketing aholes decided they could make hard disks look bigger
using decimal byte values instead of binary-based values. Note that as
far as we know, the OP stated the spec for the adapter, not the USB hub
itself (which it appears the OP doesn't have). If it is rated at 1A
than that it's total max output. If it were used for a 2-port USB hub
then each port would have .5A (probably a bit less since the internal
circuitry consumes some power). If it is a 4-port USB hub as the OP
states than the max with 100% efficiency in the circuitry would be just
.25A per port. I doubt the rating printed on the power adapter reflects
anything about the rated output of each port on the separate USB hub
device. But then maybe the OP gave us the spec for the entire product
(adapter + hub) or he gave us what he saw printed on the adapter.
Click to expand...

Good info. Thanks Vanguard
 
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