On Saturday, November 12, 2022 at 9:07:06 AM UTC-5, Joe wrote:
> On Sat, 12 Nov 2022 12:03:58 -0000
> "Commander Kinsey" <C...@nospam.com> wrote:
>
> > On Sat, 12 Nov 2022 11:15:00 -0000, John Walliker
> > <jrwal...@gmail.com> wrote:
> >
> > > On Saturday, 12 November 2022 at 08:57:35 UTC, Commander Kinsey
> > > wrote:
> > >> On Sat, 12 Nov 2022 07:39:17 -0000, Ricky
> > >> <gnuarm.del...@gmail.com> wrote:
> > >> > On Saturday, November 12, 2022 at 2:37:14 AM UTC-4, Commander
> > >> > Kinsey wrote:
> > >> >> On Sat, 12 Nov 2022 04:03:04 -0000, Paul
> > >> >> <nos...@needed.invalid> wrote:
> > >> >> > Other cabling schemes may use more "active"
> > >> >> > means of signaling. "Passive" cabling (where
> > >> >> > there is no D+ D- continuity, but there is resistor
> > >> >> > straps on D+ D- on the cable output end) are generally
> > >> >> > limited to lower currents.
> > >> >> WTF? These are charging cables, specifically designed to
> > >> >> charge! No data lines, fast charging expected!
> > >> >
> > >> > Try using your ohm meter.
> > >> >
> > >> > Wouldn't the resistors be in the power unit? It makes no sense
> > >> > to have anything in the cable unless the currents are so high,
> > >> > they would overheat a typical cable.
> > >> Charging cables have no connection on the data lines, they
> > >> advertise them as being secure - you can charge your phone on an
> > >> aeroplane or in a cafe without risking someone hacking into your
> > >> phone. So resistors on data lines within the power supply cannot
> > >> possibly do anything if you're using a charging cable.
> > >>
> > >> So.... how does a device and power supply work out what rate to
> > >> charge? In the absence of data lines, does the device just go for
> > >> it flat out until the voltage drop on the power supply causes it
> > >> to use less?
> > >
> > > Yes, that is exactly what happens with older chargers.
> >
> > There were some modems back in the days of USB 2, which drew about
> > 570mA. Some motherboards were shutting the USB socket off when they
> > did that.
> >
> > > Things get more complex with PD
> > > chargers as the voltage can be negotiated. All chargers start at
> > > 5V but some can also deliver 9V, 12V, 15V and 20V and in some cases
> > > lots of smaller steps in between. My pixel3a phone likes to charge
> > > at 9V for example. I have a notebook PC that prefers to charge at
> > > 20V. if it can. Very high power USB chargers can deliver up to 48V
> > > at up to 5A giving a maximum output power of 240W.
> > > The more exotic combinations (more than 20V or more than 3A) will
> > > only work with special cables that have identity chips which
> > > specify the current and voltage rating of the cable and connectors.
> > >
> >
> > Grrrr. My phone takes no more than 5V 1.1A. Takes quite a while to
> > charge if the CPU is running flat out all 8 cores.
> Surely nowadays the charger is in the device being charged, and is fed
> the 5V (or whatever) directly?

For modern devices like cell phones and tablets, part of the charger is
in the device, part in the charger it's connected to. Modern devices conform
to either Quickcharge or PD power specs that specify many possible
charging voltages and currents. The device being charged negotiates with
the wall charger over the USB, the wall charger tells it what it's capable of
and then the device tells the charger what it wants. The charging voltage
requested can also change as the battery is partially charged.