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What sets the charging rate?

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  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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#57830 — What sets the charging rate?

I own an Asus ZenPad S 8, I have recently discovered what I consider 
unusual behavior. I charge the pad with either a USB 3.0 port on my 
computer, or an Anker wall charger that provides 39W to two USB slots. I 
noticed that at times, the wall charger was not keeping up with the battery 
discharge in use. And I wasn't watching movies or doing any big cpu tasks 
at the time. The heaviest load I see is when I am looking at Imgur, with 
its occasional GIFs and short video clips.
I purchased one of those power monitors that goes between the power source 
and the device being charged, and no matter which charging source I am 
using, it only shows .5 amps being drawn. So my question is, what controls 
the charging rate on an android device, and how can I track down whatever 
is draining my battery?

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#57833

Tim <onelydad58@gmail.com> wrote in
news:XnsA9A3AB9A1184Btimothybilyahoocom@69.16.179.29: 

> I own an Asus ZenPad S 8, I have recently discovered what I consider 
> unusual behavior. I charge the pad with either a USB 3.0 port on my 
> computer, or an Anker wall charger that provides 39W to two USB slots.
> I noticed that at times, the wall charger was not keeping up with the
> battery discharge in use. And I wasn't watching movies or doing any
> big cpu tasks at the time. The heaviest load I see is when I am
> looking at Imgur, with its occasional GIFs and short video clips.
> I purchased one of those power monitors that goes between the power
> source and the device being charged, and no matter which charging
> source I am using, it only shows .5 amps being drawn. So my question
> is, what controls the charging rate on an android device, and how can
> I track down whatever is draining my battery?
> 
Znother data point: I hooked up my Maxboost Electron power bank, and it is 
charging at 1 amp. The port it is connected to is capable of outputing 
2.1A.

BTW If anyone happens to have a user guide or manual for a Maxboot Electron 
Plus 15000 mAh power bank, could you let me know?

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#57855

In comp.mobile.android, on Sat, 24 Nov 2018 04:24:18 GMT, Tim
<onelydad58@gmail.com> wrote:

>Tim <onelydad58@gmail.com> wrote in
>news:XnsA9A3AB9A1184Btimothybilyahoocom@69.16.179.29: 
>
>> I own an Asus ZenPad S 8, I have recently discovered what I consider 
>> unusual behavior. I charge the pad with either a USB 3.0 port on my 
>> computer, or an Anker wall charger that provides 39W to two USB slots.
>> I noticed that at times, the wall charger was not keeping up with the
>> battery discharge in use. And I wasn't watching movies or doing any
>> big cpu tasks at the time. The heaviest load I see is when I am
>> looking at Imgur, with its occasional GIFs and short video clips.
>> I purchased one of those power monitors that goes between the power
>> source and the device being charged, and no matter which charging
>> source I am using, it only shows .5 amps being drawn. So my question
>> is, what controls the charging rate on an android device, and how can
>> I track down whatever is draining my battery?
>> 
>Znother data point: I hooked up my Maxboost Electron power bank, and it is 
>charging at 1 amp. The port it is connected to is capable of outputing 
>2.1A.

That's interesting. 

I thought the major factors in charging rates were 1) the maximum the
charger could put out, and - I'm not sure abou this one - 2) the amount
in  the battery at the moment which determined how much voltage it had
and now much it pushed back against being charged.   I guess 2 would
have to mean that phone batteries when moderately to fully charged have
more volts than what they say, but that the output voltage is regulated
to a lower number.   

But when attempting to recharge of course the output regulation is
irrelevant and what matters is the actual voltage of the battery, and
that the more fully charged it is, the more voltage and the more it
pushes back, so the actual charging voltage is the difference between
the charger and the battery voltages.   And after that I = E/R where R
is the internal resistance of the battery, E is the differential
voltage, and I is the current charging current. 


>BTW If anyone happens to have a user guide or manual for a Maxboot Electron 
>Plus 15000 mAh power bank, could you let me know?

On a related topic, because I was in the hospital for 3 days (and
thought it would be 4 hours or I would have brought a charger (they
would have charged it for me probably)), I ran the battery down to 40%.

When rechaging I left the screen on to slow the charging rate, because I
thought that was better for the battery.  Is that true?  Is there any
reason it's not true when it is true for car batteries afaik.  So I
would leave my lights on and the heater fan blowing to slow but not stop
the charging.   Why would phone batteries be different.

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#57864

On 25/11/2018 06.10, micky wrote:

> When rechaging I left the screen on to slow the charging rate, because I
> thought that was better for the battery.  Is that true?  Is there any
> reason it's not true when it is true for car batteries afaik.  So I
> would leave my lights on and the heater fan blowing to slow but not stop
> the charging.   Why would phone batteries be different.

Because there is a charging controller.

It probably charges slower, but not necessarily so.

For the car, just use a smaller charger instead.

-- 
Cheers, Carlos.

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#57882

In comp.mobile.android, on Sun, 25 Nov 2018 14:12:55 +0100, "Carlos
E.R." <robin_listas@es.invalid> wrote:


So was the first part of my answer okay. 

>On 25/11/2018 06.10, micky wrote:
>
>> When rechaging I left the screen on to slow the charging rate, because I
>> thought that was better for the battery.  Is that true?  Is there any
>> reason it's not true when it is true for car batteries afaik.  So I
>> would leave my lights on and the heater fan blowing to slow but not stop
>> the charging.   Why would phone batteries be different.
>
>Because there is a charging controller.
>
>It probably charges slower, but not necessarily so.
>
>For the car, just use a smaller charger instead.

The car is usually running at the time.   Of course now that the dash
doesn't have an ammeter, or even a voltmeter, I can't tell what's going
on. 

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#57897

On 26/11/2018 03.22, micky wrote:
> In comp.mobile.android, on Sun, 25 Nov 2018 14:12:55 +0100, "Carlos
> E.R." <robin_listas@es.invalid> wrote:
> 
> 
> So was the first part of my answer okay. 
> 
>> On 25/11/2018 06.10, micky wrote:
>>
>>> When rechaging I left the screen on to slow the charging rate, because I
>>> thought that was better for the battery.  Is that true?  Is there any
>>> reason it's not true when it is true for car batteries afaik.  So I
>>> would leave my lights on and the heater fan blowing to slow but not stop
>>> the charging.   Why would phone batteries be different.
>>
>> Because there is a charging controller.
>>
>> It probably charges slower, but not necessarily so.
>>
>> For the car, just use a smaller charger instead.
> 
> The car is usually running at the time.   Of course now that the dash
> doesn't have an ammeter, or even a voltmeter, I can't tell what's going
> on. 

Ah, a running car. Well, the car has a battery charging controller, too.
Old times it was a relay that would insert o remove a coil on the
generator inductor. Now I suppose it is some sophisticated electronic
regulator.

-- 
Cheers, Carlos.

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#57928

In comp.mobile.android, on Mon, 26 Nov 2018 15:21:26 +0100, "Carlos
E.R." <robin_listas@es.invalid> wrote:

>On 26/11/2018 03.22, micky wrote:
>> In comp.mobile.android, on Sun, 25 Nov 2018 14:12:55 +0100, "Carlos
>> E.R." <robin_listas@es.invalid> wrote:
>> 
>> 
>> So was the first part of my answer okay. 
>> 
>>> On 25/11/2018 06.10, micky wrote:
>>>
>>>> When rechaging I left the screen on to slow the charging rate, because I
>>>> thought that was better for the battery.  Is that true?  Is there any
>>>> reason it's not true when it is true for car batteries afaik.  So I
>>>> would leave my lights on and the heater fan blowing to slow but not stop
>>>> the charging.   Why would phone batteries be different.
>>>
>>> Because there is a charging controller.
>>>
>>> It probably charges slower, but not necessarily so.
>>>
>>> For the car, just use a smaller charger instead.
>> 
>> The car is usually running at the time.   Of course now that the dash
>> doesn't have an ammeter, or even a voltmeter, I can't tell what's going
>> on. 
>
>Ah, a running car. Well, the car has a battery charging controller, too.
>Old times it was a relay that would insert o remove a coil on the
>generator inductor. Now I suppose it is some sophisticated electronic
>regulator.

My last car, I had to buy a battery right after I bought the used car,
and I treated it very badly and thought I'd ruined it, and I still think
that but still made it last 6 years.  Then a week before I sold it, I
had to buy another battery anyhow.  Life would have been simpler if I'd
bought it 3 years ago. 

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#57856

In article <XnsA9A3E3EAE3CFAtimothybilyahoocom@69.16.179.29>, Tim
<onelydad58@gmail.com> wrote:

> > 
> Znother data point: I hooked up my Maxboost Electron power bank, and it is 
> charging at 1 amp. The port it is connected to is capable of outputing 
> 2.1A.

that means the device you plugged into it only draws 1a. 

> BTW If anyone happens to have a user guide or manual for a Maxboot Electron 
> Plus 15000 mAh power bank, could you let me know?

there's not a lot to a power bank. connect devices to the usb-a ports
and charge it via the micro-usb charging port.

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#57890

nospam <nospam@nospam.invalid> wrote in
news:251120180042485229%nospam@nospam.invalid: 

> In article <XnsA9A3E3EAE3CFAtimothybilyahoocom@69.16.179.29>, Tim
> <onelydad58@gmail.com> wrote:
> 
>> > 
>> Znother data point: I hooked up my Maxboost Electron power bank, and
>> it is charging at 1 amp. The port it is connected to is capable of
>> outputing 2.1A.
> 
> that means the device you plugged into it only draws 1a. 
> 
But the USB 3 ports on my computer provide 1.5A, so why doesn't it charge 
at that rate rather than .5A?

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#57894

In article <XnsA9A6336EF683timothybilyahoocom@69.16.179.28>, Tim
<onelydad58@gmail.com> wrote:

> >> Znother data point: I hooked up my Maxboost Electron power bank, and
> >> it is charging at 1 amp. The port it is connected to is capable of
> >> outputing 2.1A.
> > 
> > that means the device you plugged into it only draws 1a. 
> > 
> But the USB 3 ports on my computer provide 1.5A, so why doesn't it charge 
> at that rate rather than .5A?

it can provide *up* *to* 1.5a. if a device only requests 500ma, then
that's what it gets.

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#57895

nospam <nospam@nospam.invalid> wrote in
news:261120180852212967%nospam@nospam.invalid: 

> In article <XnsA9A6336EF683timothybilyahoocom@69.16.179.28>, Tim
> <onelydad58@gmail.com> wrote:
> 
>> >> Znother data point: I hooked up my Maxboost Electron power bank,
>> >> and it is charging at 1 amp. The port it is connected to is
>> >> capable of outputing 2.1A.
>> > 
>> > that means the device you plugged into it only draws 1a. 
>> > 
>> But the USB 3 ports on my computer provide 1.5A, so why doesn't it
>> charge at that rate rather than .5A?
> 
> 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?

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#57896

In article <XnsA9A6520002E70timothybilyahoocom@69.16.179.29>, Tim
<onelydad58@gmail.com> wrote:

> >> >> Znother data point: I hooked up my Maxboost Electron power bank,
> >> >> and it is charging at 1 amp. The port it is connected to is
> >> >> capable of outputing 2.1A.
> >> > 
> >> > that means the device you plugged into it only draws 1a. 
> >> > 
> >> But the USB 3 ports on my computer provide 1.5A, so why doesn't it
> >> charge at that rate rather than .5A?
> > 
> > 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?

how do you know it was requesting 1a? 

the device and charger negotiate charging current. if the usb cable is
non-compliant, that may not work correctly.

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#57899

nospam <nospam@nospam.invalid> wrote in
news:261120180911493039%nospam@nospam.invalid: 

> In article <XnsA9A6520002E70timothybilyahoocom@69.16.179.29>, Tim
> <onelydad58@gmail.com> wrote:
> 
>> >> >> Znother data point: I hooked up my Maxboost Electron power
>> >> >> bank, and it is charging at 1 amp. The port it is connected to
>> >> >> is capable of outputing 2.1A.
>> >> > 
>> >> > that means the device you plugged into it only draws 1a. 
>> >> > 
>> >> But the USB 3 ports on my computer provide 1.5A, so why doesn't it
>> >> charge at that rate rather than .5A?
>> > 
>> > 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?
> 
> how do you know it was requesting 1a? 
> 
> the device and charger negotiate charging current. if the usb cable is
> non-compliant, that may not work correctly.
> 
As I stated before, I used a USB power monitor between my powerbank and my 
Zenpad. That is where I got all my numbers.

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#57902

In article <XnsA9A66331BD5E2timothybilyahoocom@69.16.179.28>, Tim
<onelydad58@gmail.com> wrote:

> >> But it was 'requesting' one amp from the power bank. Why not do so
> >> from the wall charger?
> > 
> > how do you know it was requesting 1a? 
> > 
> > the device and charger negotiate charging current. if the usb cable is
> > non-compliant, that may not work correctly.
> > 
> As I stated before, I used a USB power monitor between my powerbank and my 
> Zenpad. That is where I got all my numbers.

that shows the current flow, not what the device requested and what the
host granted.

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#57903

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:
> > 
> >> >> Znother data point: I hooked up my Maxboost Electron power bank,
> >> >> and it is charging at 1 amp. The port it is connected to is
> >> >> capable of outputing 2.1A.
> >> > 
> >> > that means the device you plugged into it only draws 1a. 
> >> > 
> >> But the USB 3 ports on my computer provide 1.5A, so why doesn't it
> >> charge at that rate rather than .5A?
> > 
> > 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?

  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.

  If your power monitors can also measure current and voltage, you might
want to check if different voltages explain the seemingly inconsistent
currents.

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#57904

On 11/26/2018 9:19 AM, Frank Slootweg wrote:

> 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.

An earlier Samsung tablet of mine would only give full charge current
using the ORIGINAL charger. Any other charger, no matter the size or
brand, would charge verrrry slowly and the battery symbol would show a 
red no charge indication.

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#57907

In article <pth791$88p$1@dont-email.me>, 123456789 <12345@12345.com>
wrote:

> > 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.
> 
> An earlier Samsung tablet of mine would only give full charge current
> using the ORIGINAL charger. Any other charger, no matter the size or
> brand, would charge verrrry slowly and the battery symbol would show a 
> red no charge indication.

some companies lock things down, while others do not:
<https://images.techhive.com/images/article/2016/03/usb_c_laptop_chartin
g-100649896-orig.png>

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#57906

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. 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.)
>
>  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).
-- 
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Have you ever heard about a petition, disagreed with it, but been frustrated
that there's no way you can *show* that you disagree? If so, have a look at
https://petition.parliament.uk/petitions/232770 - and please pass it on if you
agree, especially to twitter, facebook, gransnet/mumsnet, or any such forum.

You cannot simply assume someone is honest just because they are not an MP.

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#57908

In article <+IGvF2XTTC$bFwpy@255soft.uk>, J. P. Gilliver (John)
<G6JPG-255@255soft.uk> 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.)

exactly.

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#57910

"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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