I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

On 1/31/2017 3:26 PM, DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

It shouldn't.

DerbyBorn wrote:

I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No, devices pull whatever current as they require (subject to agreeing
the maximum with the charger) the charger doesn't "ram" all it's capable
of into the device ...

On Tue, 31 Jan 2017 15:26:08 GMT, DerbyBorn
wrote:

I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No. For the same reason that a car battery can crank the starter motor
that requires 100A or more yet also operate the interior light and
radio that doesn't.



--

Graham.

%Profound_observation%

On 31/01/2017 15:45, Graham. wrote:
On Tue, 31 Jan 2017 15:26:08 GMT, DerbyBorn
wrote:

I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No. For the same reason that a car battery can crank the starter motor
that requires 100A or more yet also operate the interior light and
radio that doesn't.

The only one that can sometimes cause trouble is a charger only good for
the basic 1.2A current and an impolite device that tries to take 2.4A
from it without negotiating the higher charge rate.

I don't have any device that bad, but I do have some that will slowly
discharge if put onto a basic 1.2A capable charger whist being used.

--
Regards,
Martin Brown

On Tuesday, 31 January 2017 15:40:44 UTC, Andy Burns wrote:
DerbyBorn wrote:

I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No, devices pull whatever current as they require (subject to agreeing
the maximum with the charger) the charger doesn't "ram" all it's capable
of into the device ...

That's one of the thimngs our studetn have trouble understanding at first, maybe they have those galaxy note 7 phones ;-)

whisky-dave wrote in
:

On Tuesday, 31 January 2017 15:40:44 UTC, Andy Burns wrote:
DerbyBorn wrote:

I have just bought a 13amp socket with built in USB Charger and
realise now that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No, devices pull whatever current as they require (subject to
agreeing the maximum with the charger) the charger doesn't "ram" all
it's capable of into the device ...

That's one of the thimngs our studetn have trouble understanding at
first, maybe they have those galaxy note 7 phones ;-)

I am okay on ordinary electrics - but thought their might be a "gotcha"
with phones/ tablets. There were scare storys some time back about Apple
devices catching fire on incorrect chargers.

On Tuesday, 31 January 2017 16:11:43 UTC, DerbyBorn wrote:
whisky-dave wrote in
:

On Tuesday, 31 January 2017 15:40:44 UTC, Andy Burns wrote:
DerbyBorn wrote:

I have just bought a 13amp socket with built in USB Charger and
realise now that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

No, devices pull whatever current as they require (subject to
agreeing the maximum with the charger) the charger doesn't "ram" all
it's capable of into the device ...

That's one of the thimngs our studetn have trouble understanding at
first, maybe they have those galaxy note 7 phones ;-)

I am okay on ordinary electrics - but thought their might be a "gotcha"
with phones/ tablets. There were scare storys some time back about Apple
devices catching fire on incorrect chargers.

Any device attached to the wrong charger could cause problems.
I have a few PSU for raspberry Pi whose output is 5.2V at 2amps.

I'm not sure what the maxium voltage an iPhone or any other phone can take.
But over Xmas I was charging a small cylidrical 2200ma battery left it on 24 hours and a little later the charge went pop and I saw a few sparks there was a black mark on the USB lead and the charger now rattles a 5V 1 amp Gear4.

Incedently the batter was cold and there was no sign that it was being charging when it went pop.

In article 2,
DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise
now that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

Does a 13 amp socket fry a 60 watt table light?

--
*Happiness is seeing your mother-in-law on a milk carton

Dave Plowman London SW
To e-mail, change noise into sound.

whisky-dave wrote:

I have a few PSU for raspberry Pi whose output is 5.2V [snip]
I'm not sure what the maxium voltage an iPhone or any other phone can take.

The USB spec is 5V +/- 5% so 5.2V is within tolerance.

"DerbyBorn" wrote in message
2.222...
I have just bought a 13amp socket with built in USB Charger and realise
now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

Nope. That specifies the maximum current that it can supply.
It’s the voltage that can fry things if its wrong.

I would hope not. It t would be a very dodgy design that could draw more
current than its supposed to.
Or am I too trusting?
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"DerbyBorn" wrote in message
2.222...
I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

If you are really worried an in car fuseholder with a slo blow 2A fuse
should set your mind at rest.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"newshound" wrote in message
o.uk...
On 1/31/2017 3:26 PM, DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise
now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

It shouldn't.

On Tuesday, January 31, 2017 at 3:26:10 PM UTC, DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.


The opposite problem can arise, like my iPad mini will not charge at all on a 2A charger, but is OK on a 2.4A Belkin one, even with a third party non-Apple cable.
It charges when switched off completely, but then overcharges as its regulator is also off.

On Tuesday, 31 January 2017 16:52:42 UTC, Dave Plowman (News) wrote:
In article 2,
DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise
now that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

Does a 13 amp socket fry a 60 watt table light?

Denps which student fits it ;-)

On Wednesday, 1 February 2017 11:10:28 UTC, Brian Gaff wrote:
I would hope not. It t would be a very dodgy design that could draw more
current than its supposed to.
Or am I too trusting?
Brian


Ask samsung.

On Wednesday, 1 February 2017 13:56:45 UTC, therustyone wrote:
On Tuesday, January 31, 2017 at 3:26:10 PM UTC, DerbyBorn wrote:
I have just bought a 13amp socket with built in USB Charger and realise now
that it is 3.1 amps.


The opposite problem can arise, like my iPad mini will not charge at all on a 2A charger, but is OK on a 2.4A Belkin one, even with a third party non-Apple cable.
It charges when switched off completely, but then overcharges as its regulator is also off.

I have an old iphone chareg iphone4 I think, that when conected to an ipad air 2
charges for about half a second then the ipad goes off then back on again then off like a ticking clock.

therustyone wrote
DerbyBorn wrote

I have just bought a 13amp socket with built in
USB Charger and realise now that it is 3.1 amps.

The opposite problem can arise, like my iPad mini will
not charge at all on a 2A charger, but is OK on a 2.4A
Belkin one, even with a third party non-Apple cable.

Thats a different effect and has nothing to
do with the maximum current it can provide.

It charges when switched off completely,

Because it isnt using any of what the
charger is supplying to power the device.

but then overcharges as its regulator is also off.

No its not.

Brian Gaff wrote

I would hope not. It t would be a very dodgy design that could draw more
current than its supposed to.

Or am I too trusting?

Nope, he just doesn’t understand how volts and amps work.

"DerbyBorn" wrote in message
2.222...
I have just bought a 13amp socket with built in USB Charger and realise
now
that it is 3.1 amps.

Will it fry my Samsung which specifies 2 amps?

On Wed, 01 Feb 2017 11:11:23 +0000, Brian Gaff wrote:

If you are really worried an in car fuseholder with a slo blow 2A fuse
should set your mind at rest.

No, it won't (even if there was any need)!

This question ("Can I use this 2A USB rated socket to charge my half amp
rated gadget or charger?") comes up with monotonous regularity in the
news groups. It's akin to asking if a 240v 40W table lamp (0.167A
incandescent lamp load) can be safely plugged into a 240v 13A socket. The
answer in both cases is "Yes!" and for essentially the same reason.

When supplying electrical power to an electrical appliance or gadget,
the primary consideration is the matching of the supply voltage to the
voltage required by the appliance or gadget. With mains powered
appliances and gadgets fitted with 13A plugs, the 230/240v is implied in
the case of UK domestic supply and appliances and gadgets (and always
marked in some way on the plug in appliance or gadget itself for the
benefit of any "Doubting Thomases").

The same rule applies in the case of low powered gadgets intended to be
powered from low level DC voltages (typically 3 to 30 but more commonly 5
or 12 volts) using 'wallwarts' which may take the form of a "USB Charging
'wallwart'" (plug in or built into something else like a PC or a 13A
double outlet wall socket).

Naturally, due to the variance in DC voltage levels used by such low
voltage gadgets (commonly 5 or 12 volts but possibly as low as 3 to as
high as 30 volts) end users tend (and most definitely ought) to verify
that the voltages match between any chosen 'wallwart' and its associated
gadget to guard against the possible mix up of an identical looking but
different voltage wallwart[1]

It's understandable that such concerns should arise out of this scenario
(mistakenly using the wrong voltage wallwart). However, with USB gadgets
and chargers, the voltage level has long been standardised on the classic
five volt standard originating with the TTL chips used by the original
desktop computers (Apple and IBM and all the toy computers of the late
70s onwards to the present day).

As with wallwarts designed not for charging but simply to act as a low
voltage power supply, the only critical specification for 'safe'
operation is the voltage level. With USB this is defined as 5 volts[2].
The charging amperage specified by such chargers are a maximum they can
supply before they either current limit or else foldback into an overload
induced tripped off state.

If you plug a gadget, designed to charge its own built in battery from a
standard USB port specified to supply no more than half an amp per socket
[3], into a 2 or 3 amp rated USB charger, said gadget will still only
draw the maximum of half an amp unless it has the means to identify
whether the supply is capable of supplying more current than the nominal
half amp limit of a standard USB port *and*, importantly, the ability to
make use of the higher charging current.

IOW, a 2A rated Samsung gadget will work just fine with a 3.1A rated USB
charging port. Indeed, a 2A (maximum charging rate) Samsung gadget will
work just fine (at least for charging purposes) off a half amp limited
USB2 port. The Samsung will use whatever it can get to charge its
battery, even if it's an unnegotiated 100mA from a laptop, netbook or
tablet USB port (it'll just take a lot longer to charge its battery
compared to how fast it can charge from a 2 or 3 amp rated port).

Some gadgets may draw so much current when turned on that they leave so
little current available from a half amp supply as to take a day or two
to fully recharge their battery. In this case, the benefit would be to
extend the operating time without exhausting the battery.

Using a 3.1A rated USB charging port would allow the device to be
powered up and *still* recharge its battery at the full 2 amp rate with
600mA to spare for another USB device. However, a gadget with a 2A
battery charging capability may be forced to reduce the battery charging
rate when also switched on and active at the same time due to limitations
in its power management circuitry.

[1] Due to the mass market nature of these 'handy gadgets', it's not
unusual to land up with a collection of identical looking wallwarts with
different DC voltage outputs (commonly, though not restricted to, a mix
of 5 and 12 volts). Luckily, other than for kit that depends on the
supply being a specific voltage to power a motor or solenoid, the innards
often need one or more supply voltages such as 3.3v and 5v demanding some
form of voltage regulator which, these days will be a low loss, high
efficiency switching converter.

A surprising amount of electronic kit (SoHo ethernet switches and
routers for example) will run just fine off almost any wallwart
regardless of the voltage over the range of 6 to 16 volts DC despite what
is specified by the gadget itself provided the wallwart's VA rating
equals or exceeds that specified by the gadget. However, it's a given
that anything designed to be powered via a USB2 socket cannot be safely
subjected to a voltage in excess of 5.5v (nominal 5v +/- 10% tolerance).

[2] The USB3 standard not only permits a higher current demand to be met,
it also allows for a higher negotiated supply voltage, presumably
starting off with a 5 volt level for safe interoperability with USB1 and
2 and 'dumb' USB3 devices.

[3] IME thus far, the USB2 ports on desktop PC motherboards supply their
USB sockets and headers via a common 5v bus, protected by a 3 or 4 amp
rated polyfuse[4] which not only powers the USB sockets but also, where
fitted, the 5v pins on the PS/2 keyboard and mouse sockets.

It seems the 'Negotiated 500mA' protocol mechanism is restricted to
laptop/tablet usage where power consumption is a more critical
consideration. In theory (which only happens in practice with portable
devices), a usb gadget can only draw a maximum of 100mA without
negotiating for the additional 400mA it may desire.

[4] In some cases, notably those infamous "PC Chips" branded
motherboards, the cost of a polyfuse was deemed an unnecessary expense by
the bean counters who felt their safety obligations could be met
adequately by reliance on either a very thin circuit trace or a small smd
inductor to act as a 'one shot' safety fuse to obviate the risk of
conflagration in the event of a short circuit fault on the 5v USB power
bus.

--
Johnny B Good

On Tue, 31 Jan 2017 18:17:14 +0000, Andy Burns wrote:

whisky-dave wrote:

I have a few PSUs for raspberry Pi whose output is 5.2V [snip]
I'm not sure what the maximum voltage an iPhone or any other phone can
take.

The USB spec is 5V +/- 5% so 5.2V is within tolerance.

The loads (eg TTL chips and their cmos equivilents) have a +/-10%
voltage tolerance rating whilst it's common practice to specify PSU
voltage tolerances at half of such loads' tolerance rating to absolutely
guarantee that the chips will operate to their specified limits with a
margin to spare, hence the +/-5% voltage tolerance commonly specified for
PSUs.

However with USB powered kit, relying on a 'nominal five volt supply'
with a +/-5% tolerance (4.75 to 5.25 volts) to power 'five volt kit' with
its own 'nominal five volt' +/-10% requirement (4.5 to 5.5 volts) over
the vagaries of ill defined cable and contact resistances can lead to out
of tolerance conditions on the supply pins of the chips used in the USB
device or gadget since the 250mV margin between the lower limits of 4.75v
supply and 4.5v load can be entirely consumed (and then some) by volt
drops in the cable resistance and socket contact resistances depending on
the amount of current demanded. Even just a half amp loading could result
in more than 250mV being lost in the connecting cabling alone.

Awareness of this cabling volt drop issue leads to USB wallwarts being
specified to a higher and more tightly controlled voltage level with 5.2v
+/-2.5% being typical (5.07v min and 5.33v max) allowing a worst case
cable volt drop allowance of 507mV.

An obvious way to eliminate the cable volt drop issue is to use remote
voltage sensing wires in the cable between the wallwart PSU and the pins
of the usb plug on the end of a permanently attached cable (dedicated
high current USB chargers). This means the 5.2v supply can be maintained
at the USB plug contacts independently of volt drops arising out of the
normal current variations supplied through the cable, leaving only
contact resistance as the final 'unknown' parameter.

Whilst a connector will eventually start producing excessive volt drops
due to wear and tear, using remote voltage sensing will mitigate this by
allowing for longer and more flexible (but higher resistance) leads
reducing the stresses transferred into the plug and socket assembly.
Also, the higher resistance of the lead will reduce the peak arcing
currents due to contact movement, reducing electrical erosion of said
contacts, leading to an improved reliability all round.

There can be a world of difference between a "Cheap 'n' Cheerful" "No
Frills" "2A USB charger" and that of a well designed dedicated "Fast" 2
or 3 amp USB charger using remote sensing at the USB plug on the end of a
2 metre flexible cord.

Since those 13A wall sockets with built in USB charging ports can't
provide a remote voltage sensing facility, they seem a rather pointless
add-on feature imho. A decent plug in wallwart is a much better option
since it can include the refinement of remote sensing and a more
optimised tightly controlled voltage of 5.2 or 5.3 volts at its
permanently connected USB plug.

With a little more expense, even the dedicated USB charging lead could
be made a user servicable part of such a fast charging USB wallwart.
However, I can see a case for not adding such expense on the basis that
by the time such a well designed plug and fly-lead has worn itself out,
it's very likely time to replace the smoothing capacitors in the wallwart
itself and therefore the whole damn thing anyway.

--
Johnny B Good

OK on another issue then...
Powering a usb sound box from the computer seems to result in a whine on
the analogue audio output of said device. One assumes as this changes as
things happen in the computer that this is getting in via the psu lead from
the computer via the usb. So if one bought one of these oft used powered usb
hubs, could I expect this to go, or would I still be plagued by this either
due to the signal still getting down one of the digital inputs or by there
being a not very well designed wall wart on the remote hub.
My first thought would be to buy a well known make and hope for the best,
but if this fails, could one open up the sound box and get some nice kind
person to put some really big capacitors across the 5v supply?
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Johnny B Good" wrote in message
...
On Tue, 31 Jan 2017 18:17:14 +0000, Andy Burns wrote:

whisky-dave wrote:

I have a few PSUs for raspberry Pi whose output is 5.2V [snip]
I'm not sure what the maximum voltage an iPhone or any other phone can
take.

The USB spec is 5V +/- 5% so 5.2V is within tolerance.

The loads (eg TTL chips and their cmos equivilents) have a +/-10%
voltage tolerance rating whilst it's common practice to specify PSU
voltage tolerances at half of such loads' tolerance rating to absolutely
guarantee that the chips will operate to their specified limits with a
margin to spare, hence the +/-5% voltage tolerance commonly specified for
PSUs.

However with USB powered kit, relying on a 'nominal five volt supply'
with a +/-5% tolerance (4.75 to 5.25 volts) to power 'five volt kit' with
its own 'nominal five volt' +/-10% requirement (4.5 to 5.5 volts) over
the vagaries of ill defined cable and contact resistances can lead to out
of tolerance conditions on the supply pins of the chips used in the USB
device or gadget since the 250mV margin between the lower limits of 4.75v
supply and 4.5v load can be entirely consumed (and then some) by volt
drops in the cable resistance and socket contact resistances depending on
the amount of current demanded. Even just a half amp loading could result
in more than 250mV being lost in the connecting cabling alone.

Awareness of this cabling volt drop issue leads to USB wallwarts being
specified to a higher and more tightly controlled voltage level with 5.2v
+/-2.5% being typical (5.07v min and 5.33v max) allowing a worst case
cable volt drop allowance of 507mV.

An obvious way to eliminate the cable volt drop issue is to use remote
voltage sensing wires in the cable between the wallwart PSU and the pins
of the usb plug on the end of a permanently attached cable (dedicated
high current USB chargers). This means the 5.2v supply can be maintained
at the USB plug contacts independently of volt drops arising out of the
normal current variations supplied through the cable, leaving only
contact resistance as the final 'unknown' parameter.

Whilst a connector will eventually start producing excessive volt drops
due to wear and tear, using remote voltage sensing will mitigate this by
allowing for longer and more flexible (but higher resistance) leads
reducing the stresses transferred into the plug and socket assembly.
Also, the higher resistance of the lead will reduce the peak arcing
currents due to contact movement, reducing electrical erosion of said
contacts, leading to an improved reliability all round.

There can be a world of difference between a "Cheap 'n' Cheerful" "No
Frills" "2A USB charger" and that of a well designed dedicated "Fast" 2
or 3 amp USB charger using remote sensing at the USB plug on the end of a
2 metre flexible cord.

Since those 13A wall sockets with built in USB charging ports can't
provide a remote voltage sensing facility, they seem a rather pointless
add-on feature imho. A decent plug in wallwart is a much better option
since it can include the refinement of remote sensing and a more
optimised tightly controlled voltage of 5.2 or 5.3 volts at its
permanently connected USB plug.

With a little more expense, even the dedicated USB charging lead could
be made a user servicable part of such a fast charging USB wallwart.
However, I can see a case for not adding such expense on the basis that
by the time such a well designed plug and fly-lead has worn itself out,
it's very likely time to replace the smoothing capacitors in the wallwart
itself and therefore the whole damn thing anyway.

--
Johnny B Good

On Friday, February 10, 2017 at 3:21:10 PM UTC, Johnny B Good wrote:
On Wed, 01 Feb 2017 11:11:23 +0000, Brian Gaff wrote:

If you are really worried an in car fuseholder with a slo blow 2A fuse
should set your mind at rest.

No, it won't (even if there was any need)!

This question ("Can I use this 2A USB rated socket to charge my half amp
rated gadget or charger?") comes up with monotonous regularity in the
news groups. It's akin to asking if a 240v 40W table lamp (0.167A
incandescent lamp load) can be safely plugged into a 240v 13A socket. The
answer in both cases is "Yes!" and for essentially the same reason.

When supplying electrical power to an electrical appliance or gadget,
the primary consideration is the matching of the supply voltage to the
voltage required by the appliance or gadget. With mains powered
appliances and gadgets fitted with 13A plugs, the 230/240v is implied in
the case of UK domestic supply and appliances and gadgets (and always
marked in some way on the plug in appliance or gadget itself for the
benefit of any "Doubting Thomases").

The same rule applies in the case of low powered gadgets intended to be
powered from low level DC voltages (typically 3 to 30 but more commonly 5
or 12 volts) using 'wallwarts' which may take the form of a "USB Charging
'wallwart'" (plug in or built into something else like a PC or a 13A
double outlet wall socket).

Naturally, due to the variance in DC voltage levels used by such low
voltage gadgets (commonly 5 or 12 volts but possibly as low as 3 to as
high as 30 volts) end users tend (and most definitely ought) to verify
that the voltages match between any chosen 'wallwart' and its associated
gadget to guard against the possible mix up of an identical looking but
different voltage wallwart[1]

It's understandable that such concerns should arise out of this scenario
(mistakenly using the wrong voltage wallwart). However, with USB gadgets
and chargers, the voltage level has long been standardised on the classic
five volt standard originating with the TTL chips used by the original
desktop computers (Apple and IBM and all the toy computers of the late
70s onwards to the present day).

As with wallwarts designed not for charging but simply to act as a low
voltage power supply, the only critical specification for 'safe'
operation is the voltage level. With USB this is defined as 5 volts[2].
The charging amperage specified by such chargers are a maximum they can
supply before they either current limit or else foldback into an overload
induced tripped off state.

If you plug a gadget, designed to charge its own built in battery from a
standard USB port specified to supply no more than half an amp per socket
[3], into a 2 or 3 amp rated USB charger, said gadget will still only
draw the maximum of half an amp unless it has the means to identify
whether the supply is capable of supplying more current than the nominal
half amp limit of a standard USB port *and*, importantly, the ability to
make use of the higher charging current.

IOW, a 2A rated Samsung gadget will work just fine with a 3.1A rated USB
charging port. Indeed, a 2A (maximum charging rate) Samsung gadget will
work just fine (at least for charging purposes) off a half amp limited
USB2 port. The Samsung will use whatever it can get to charge its
battery, even if it's an unnegotiated 100mA from a laptop, netbook or
tablet USB port (it'll just take a lot longer to charge its battery
compared to how fast it can charge from a 2 or 3 amp rated port).

Some gadgets may draw so much current when turned on that they leave so
little current available from a half amp supply as to take a day or two
to fully recharge their battery. In this case, the benefit would be to
extend the operating time without exhausting the battery.

Using a 3.1A rated USB charging port would allow the device to be
powered up and *still* recharge its battery at the full 2 amp rate with
600mA to spare for another USB device. However, a gadget with a 2A
battery charging capability may be forced to reduce the battery charging
rate when also switched on and active at the same time due to limitations
in its power management circuitry.

[1] Due to the mass market nature of these 'handy gadgets', it's not
unusual to land up with a collection of identical looking wallwarts with
different DC voltage outputs (commonly, though not restricted to, a mix
of 5 and 12 volts). Luckily, other than for kit that depends on the
supply being a specific voltage to power a motor or solenoid, the innards
often need one or more supply voltages such as 3.3v and 5v demanding some
form of voltage regulator which, these days will be a low loss, high
efficiency switching converter.

A surprising amount of electronic kit (SoHo ethernet switches and
routers for example) will run just fine off almost any wallwart
regardless of the voltage

Nevertheless, you have to be careful of smart phones sold circa 5 years ago with a dedicated USB charger and the warning "only use the supplied charger". My HTC used to complain on screen if I plugged it into a universal USB charger or it got rather hot, implying that current limitation was designed into the HTC charger. Since the more recent moves not to sell chargers with new phones, current limitation is likely built into the phone and the problem has gone away.

On Sat, 11 Feb 2017 01:21:38 -0800, therustyone wrote:

On Friday, February 10, 2017 at 3:21:10 PM UTC, Johnny B Good wrote:

====snip====


A surprising amount of electronic kit (SoHo ethernet switches and
routers for example) will run just fine off almost any wallwart
regardless of the voltage

Nevertheless, you have to be careful of smart phones sold circa 5 years
ago with a dedicated USB charger and the warning "only use the supplied
charger". My HTC used to complain on screen if I plugged it into a
universal USB charger or it got rather hot, implying that current
limitation was designed into the HTC charger. Since the more recent
moves not to sell chargers with new phones, current limitation is likely
built into the phone and the problem has gone away.

When it comes to kit that's designed to be charged from a USB port
(whether on a desktop PC or a wallwart usb charger), it's best to stick
to such five volt sources. Unlike a lot of SoHo IT kit designed to be
powered from a wallwart, Tablets, Smartphones and the like are best
confined to the supplied or recommended USB chargers. You can't play
'Fast and Loose' with wallwart voltages here. It helps that the charging
cables are USB cables of one type or another in this case - you'd be hard
pressed to connect them to a DC voltage source other than a 5 or 5.2 volt
one anyway.

--
Johnny B Good

On Sat, 11 Feb 2017 08:32:43 +0000, Brian Gaff wrote:

OK on another issue then...
Powering a usb sound box from the computer seems to result in a whine
on
the analogue audio output of said device. One assumes as this changes as
things happen in the computer that this is getting in via the psu lead
from the computer via the usb. So if one bought one of these oft used
powered usb hubs, could I expect this to go, or would I still be plagued
by this either due to the signal still getting down one of the digital
inputs or by there being a not very well designed wall wart on the
remote hub.
My first thought would be to buy a well known make and hope for the
best, but if this fails, could one open up the sound box and get some
nice kind person to put some really big capacitors across the 5v supply?
Brian

The issue here is due to noise ('digital hash') being induced into the
analogue signal lines (earth loop or just plain inductive or capacitive
coupling).

In the case of a USB powered speaker box which still uses the speaker or
line out ports, the problem is simply a 5v supply polluted with 'digital
hash' not being sufficiently screened or decoupled from the analogue
signal lines. A larger decoupling capacitor across the 5v supply might
improve the situation but have no effect (or might even aggravate the
problem) if the issue is coupling between the supply wiring and the
analogue signal wiring.

If the USB sound box has its own DAC sound chip built in to convert the
digital sound stream via the USB data lines, the problem is the result of
a badly filtered 5v supply in the amplifier circuitry. In this case,
using a powered hub may alleviate the problem, assuming an analogue
regulated wallwart supply or a high quality smpsu wallwart.

A poor quality smpsu wallwart may well introduce different but similar
whining noises into the audio output. However, a capacitor upgrade in the
amplifier may well provide effective relief, depending on how the
interference is being introduced (amplifier supply itself or coupling
into the analogue line between the ADC and the amplifier).

Any 'digital hash' coupled into the USB data lines is going to be
extremely low level and its effects nulled out by the use of the balanced
line (D+ and D- wires). Even if such interference to the D+ and D- wires
was to reach a sufficiently high level as to cause trouble, the symptoms
would be data corruption of the stream leading to random pops, crackles
and bangs or just complete drop outs. Such interference wouldn't account
for 'whining' noises which are only heard by virtue of their being
induced into the analogue signal paths[1].

Assuming the usb sound box appears as a 'device' in Device Manager (ie
it has its own DAC built in), there's a good chance that a powered hub
with either an analogue or high quality smpsu wallwart will eliminate
(or, at the very least, modify[2]) the 'digital hash' whining noises
you're currently experiencing. An alternative to modifying the innards of
the USB sound box in this case would be to get an in-line filter module
made up for the wallwart to powered USB hub feed (basically something as
simple as a 1F 6.3v capacitor across the 5v line :-).

[1] A properly implemented DAC chip will prevent the 'digital hash' that
is the data stream arriving at its digital input port from being coupled
into its analogue output port. However, badly laid out circuit boards can
negate the DAC chip designers' best efforts at preventing such 'cross-
talk' issues so it's best not to assume that every implementation will be
free of this problem.

It has to be said, however, that it takes a certain level of
incompetence for such cross-talk afflicted abominations to pollute the
market (but please bear in mind the *years* we had to wait before the PCI
soundcard analogue line input clipping issue was resolved).

[2] Even if such a change merely modifies the form of the interference
rather than eliminate it, that still helps you in pinning down the
culprit so you can concentrate your efforts on more productive measures.
In this case, a change in the characteristics of the unwanted noise,
rather than elimination, may simply indicate that a better quality
wallwart is all that's needed.

--
Johnny B Good

On Friday, 10 February 2017 16:48:29 UTC, Johnny B Good wrote:
On Tue, 31 Jan 2017 18:17:14 +0000, Andy Burns wrote:

whisky-dave wrote:

I have a few PSUs for raspberry Pi whose output is 5.2V [snip]
I'm not sure what the maximum voltage an iPhone or any other phone can
take.

The USB spec is 5V +/- 5% so 5.2V is within tolerance.

The loads (eg TTL chips and their cmos equivilents) have a +/-10%

Modern chips (well of the last 10 years) are the HC series which work from
2V to 6V.
Modern memeory chips are 3,3V 2.5V and 1.8V.

voltage tolerance rating whilst it's common practice to specify PSU
voltage tolerances at half of such loads' tolerance rating to absolutely
guarantee that the chips will operate to their specified limits with a
margin to spare, hence the +/-5% voltage tolerance commonly specified for
PSUs.

Te peoblem comes with over voltage is that you can blow the regulator by overheating.


However with USB powered kit, relying on a 'nominal five volt supply'
with a +/-5% tolerance (4.75 to 5.25 volts) to power 'five volt kit' with
its own 'nominal five volt' +/-10% requirement (4.5 to 5.5 volts) over
the vagaries of ill defined cable and contact resistances can lead to out
of tolerance conditions on the supply pins of the chips used in the USB
device or gadget since the 250mV margin between the lower limits of 4.75v
supply and 4.5v load can be entirely consumed (and then some) by volt
drops in the cable resistance and socket contact resistances depending on
the amount of current demanded. Even just a half amp loading could result
in more than 250mV being lost in the connecting cabling alone.

Awareness of this cabling volt drop issue leads to USB wallwarts being
specified to a higher and more tightly controlled voltage level with 5.2v
+/-2.5% being typical (5.07v min and 5.33v max) allowing a worst case
cable volt drop allowance of 507mV.

An obvious way to eliminate the cable volt drop issue is to use remote
voltage sensing wires in the cable between the wallwart PSU and the pins
of the usb plug on the end of a permanently attached cable (dedicated
high current USB chargers). This means the 5.2v supply can be maintained
at the USB plug contacts independently of volt drops arising out of the
normal current variations supplied through the cable, leaving only
contact resistance as the final 'unknown' parameter.

Whilst a connector will eventually start producing excessive volt drops
due to wear and tear, using remote voltage sensing will mitigate this by
allowing for longer and more flexible (but higher resistance) leads
reducing the stresses transferred into the plug and socket assembly.
Also, the higher resistance of the lead will reduce the peak arcing
currents due to contact movement, reducing electrical erosion of said
contacts, leading to an improved reliability all round.

There can be a world of difference between a "Cheap 'n' Cheerful" "No
Frills" "2A USB charger" and that of a well designed dedicated "Fast" 2
or 3 amp USB charger using remote sensing at the USB plug on the end of a
2 metre flexible cord.

Since those 13A wall sockets with built in USB charging ports can't
provide a remote voltage sensing facility, they seem a rather pointless
add-on feature imho. A decent plug in wallwart is a much better option
since it can include the refinement of remote sensing and a more
optimised tightly controlled voltage of 5.2 or 5.3 volts at its
permanently connected USB plug.

With a little more expense, even the dedicated USB charging lead could
be made a user servicable part of such a fast charging USB wallwart.
However, I can see a case for not adding such expense on the basis that
by the time such a well designed plug and fly-lead has worn itself out,
it's very likely time to replace the smoothing capacitors in the wallwart
itself and therefore the whole damn thing anyway.

--
Johnny B Good