"whisky-dave" wrote in message
...
On Wednesday, 14 December 2016 14:36:18 UTC, Rod Speed wrote:
"whisky-dave" wrote in message
...
On Tuesday, 13 December 2016 18:48:38 UTC, Rod Speed wrote:
"whisky-dave" wrote in message
...
On Monday, 12 December 2016 13:33:52 UTC, charles wrote:
In article ,
Dave Plowman (News) wrote:
In article ,
Stephen wrote:
I bought an unbranded wall-wart to usb output charger from CPC,
hoping
to use it to charge my mobile phone or tablet (both are
Samsung).
When
I connect either device using the original Samsung cable,
neither
device charges.

Why is this not working? I read a post here some months ago
saying
that the PSU and the device communicate (presumably over the
data
wires) and presumably the phone tells the charger what current
it
will
accept?

Could it be that the charger I have is not that sophisticated
and
is
not talking to the phone or does Samsung employ some way of
checking
whether the supply is a Samsung charger - I'm not an Apple man
but
I
think Apple do the same?

I have a couple of Samsung devices and both charge just fine from
a
non
Samsung PS. Indeed I bought a mains socket with built in USB
charger
outlets (to make things neater than wall warts) and that charges
everything I have that uses this system.

Are you sure your new charger produces enough current?

I think that's the point. With my wife's Nokia phone, if you plug
it
into
a low current charger, a mesage appears on the screen to that
effect.

If I plug my ipad air 2 into an old iphone charger (iphone4) the
ipad
comes on
then switches off in a one second cycle something I wouldn't have
expected
as
on another old charger it just doesn't charge (battery indicator
doesn't
go green).

Most likely that one happens like that because it trys to take the
current it wants from the iphone4 charger and that sags badly
voltage wise when it does that.

There have been sonme instances of the lead causing charguing
problems but I haven't come uop against that one yet.

Yes I know but IF the ipad communicates over the data lines

It doesnt in the sense that the charger tells the phone what current it
can
provide.

That's what the version of USB does.


ALL is communicates is that it can provide more than the 500mA
that standard USB port is guaranteed to be able to provide.

What is a standard USB port ?

That 500ma they are required to be able to supply.

Keyboards can typically only suply 100ma even if USB2
Some PC's have differtn standards depending on which
USB port you plug them into. All the PCs here if yuo wanted
to power an external drive you'd have to plug them in the
back otherwise they wouldnlt spin up properly.

Thats because they need more than 500ma.

it shouldn't get itself into this situation. It'd realise
that it couldn't get enough power to charge

It clearly can provide what a standard USB port can provide.

Doesn't seem to be able to.

Of course it does, otherwise it wouldnt be
able to charge the iphone 4S it came with.

Are you saying all USB ports can supply the same current ?

Nope.

and give up trying just as my old ipad3 did when trying to get power
from the keyboard it comes up with a message telling you it's not
charging.

But it doesnt say that about a standard USB port, it does charge slowly
from that.



What is a standard USB port in your world ?

One that can supply 500ma.