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Re: What sets the charging rate?

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"J. P. Gilliver (John)" <G6JPG-255@255soft.uk> wrote:
> In message <pth9uf.bag.1@ID-201911.user.individual.net>, Frank Slootweg 
> <this@ddress.is.invalid> writes:
> >Tim <onelydad58@gmail.com> wrote:
> >> nospam <nospam@nospam.invalid> wrote in
> >> news:261120180852212967%nospam@nospam.invalid:
> >>
> >> > In article <XnsA9A6336EF683timothybilyahoocom@69.16.179.28>, Tim
> >> > <onelydad58@gmail.com> wrote:
> []
> >> >> But the USB 3 ports on my computer provide 1.5A, so why doesn't it
> >> >> charge at that rate rather than .5A?
> 
> (Same reason your 40 watt light bulb doesn't draw the kilowatt or so 
> your household lighting circuit can supply.)
> >> >
> >> > it can provide *up* *to* 1.5a. if a device only requests 500ma, then
> >> > that's what it gets.
> >> >
> >> But it was 'requesting' one amp from the power bank. Why not do so from the
> >> wall charger?
> 
> Because the two don't speak each other's language. (Or _possibly_ the 
> lead is missing the conversation wires.)
> >
> >  I've also seen such seemingly inconsistent behaviour, i.e. different
> >currents drawn from different chargers, while the *highest* current is
> >*less* than the capacity of the smallest-capacity charger.
> >
> >  For example at some state of charge (SoC), my Samsung tablet might
> >draw some 750mA from its 2.1A charger, but on a 1A (also Samsung)
> >charger, it draws only about half that, 375mA. However, when checking
> >the *voltage*, the 2.1A charger delivers 5.18V, while the 1A charger
> >delivers 4.96V.
> >
> >  So I'm quite sure that the 'inconsistent' below-charger-capacity
> >charging currents are caused by the chargers delivering slightly
> >different voltages.
> 
> I'm not. It's certainly _possible_ that the 'phones might monitor the 
> voltage available and take current accordingly, but there may also be 
> communication between the two.

  It's both (voltage monitoring and communication (the actual term is
[device] "configuration").

  There indeed is - or at least should be - communication
(configuration) between the two, but that communication (configuration)
determines the *maximum* current the source is allowed to supply. For
normal USB (2.0) ports the limits are 100mA and 500mA. USB charging
ports have additional limits of 1.5A and 5A. (Values simplified, because
before the Battery Charging Specification, there were already
ports/chargers with capacities above 500mA.)

  But the *actual* current - i.e. 750mA and 375mA in my example - is
still determined by charge controllers or/and Ohm's law.

  Without a charge controller in the device, the device could not limit
the charge to 750mA when it has asked the charger for 1.5A.

  So there's a difference between the maximum allowable current and the
actual current drawn,

<https://en.wikipedia.org/wiki/USB_(Physical)#Power>

>				 At its simplest, devices will by default 
> take no more than half an ampère, because that's what USB 1 and 2 is 
> rated at; I read that if the charger contains certain combinations of 
> resistors between the power and data lines, the 'phone will "recognise 
> it as a proper Apple charger" and draw more. More modern ones may 
> actually converse in data terms. (USB3 is rated at a higher default 
> level, but the 'phone must know it is a USB3 output - which I presume 
> means also be connected with a USB3 cable - before it will draw more 
> than the USB2 level.)

  Yep, all true. See the Wikipedia article for all the gory details.

> >  If your power monitors can also measure current and voltage, you might
> >want to check if different voltages explain the seemingly inconsistent
> >currents.
> 
> I doubt it's _purely_ the voltage level that determines it, at least for 
> something as sophisticated as a 'phone - not least because the drops in 
> the cable probably exceed the variation in supplies. For simpler loads, 
> like a desk fan or light, it might have an effect (though only in 
> proportion to the voltage variation).

  No, it's indeed not purely the voltage level, but apparently for a
lower voltage level, the charge controller in the devices 'decide' to
draw less current than for a higher voltage level.

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Thread

What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-23 22:52 +0000
  Re: What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-24 04:24 +0000
    Re: What sets the charging rate? micky <NONONOmisc07@bigfoot.com> - 2018-11-25 00:10 -0500
      Re: What sets the charging rate? "Carlos E.R." <robin_listas@es.invalid> - 2018-11-25 14:12 +0100
        Re: What sets the charging rate? micky <NONONOmisc07@bigfoot.com> - 2018-11-25 21:22 -0500
          Re: What sets the charging rate? "Carlos E.R." <robin_listas@es.invalid> - 2018-11-26 15:21 +0100
            Re: What sets the charging rate? micky <NONONOmisc07@bigfoot.com> - 2018-11-27 03:52 -0500
    Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-25 00:42 -0500
      Re: What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-26 06:18 +0000
        Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-26 08:52 -0500
          Re: What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-26 14:03 +0000
            Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-26 09:11 -0500
              Re: What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-26 15:45 +0000
                Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-26 10:49 -0500
            Re: What sets the charging rate? Frank Slootweg <this@ddress.is.invalid> - 2018-11-26 16:19 +0000
              Re: What sets the charging rate? 123456789 <12345@12345.com> - 2018-11-26 09:33 -0700
                Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-26 11:57 -0500
              Re: What sets the charging rate? "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2018-11-26 16:52 +0000
                Re: What sets the charging rate? nospam <nospam@nospam.invalid> - 2018-11-26 11:57 -0500
                Re: What sets the charging rate? Frank Slootweg <this@ddress.is.invalid> - 2018-11-26 18:49 +0000
                Re: What sets the charging rate? "Carlos E.R." <robin_listas@es.invalid> - 2018-11-27 04:09 +0100
                Re: What sets the charging rate? "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2018-11-27 16:42 +0000
                Re: What sets the charging rate? Tim <onelydad58@gmail.com> - 2018-11-27 22:43 +0000
                Re: What sets the charging rate? "Carlos E.R." <robin_listas@es.invalid> - 2018-11-28 14:08 +0100
                Re: What sets the charging rate? Andy Burns <usenet@andyburns.uk> - 2018-11-28 13:27 +0000
                Re: What sets the charging rate? "Carlos E.R." <robin_listas@es.invalid> - 2018-11-28 14:06 +0100

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