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Re: What sets the charging rate?

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In message <35pucf-i3d.ln1@Telcontar.valinor>, Carlos E.R. 
<robin_listas@es.invalid> writes:
>On 26/11/2018 17.52, J. P. Gilliver (John) 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.)
>
>Well, not exactly: the light bulb doesn't have a controller, and it
>doesn't negotiate. It is purely ohm law, with a relatively fixed plain
>resistor (except that the resistor gets so hot, that resistance
>increases notably with the temperature).
>
>So the house supplies a fixed voltage and you connect a fixed resistor:
>the current is determined from both. There is no limitation in the
>circuit on current or power: but if the resistor is too low, the fuse blows.
>
>Intelligent devices can have batteries with regulation. The apparent
>resistance the "battery" has varies so that it draws more or less
>current as needed.
>
I know, it was a poor example: I was just a bit shocked that someone 
could say "my charger delivers 1.5A"; he didn't realise that the truth 
was that his charger _can_ deliver 1.5A, but doesn't necessarily do so 
if the device doesn't suck that much. I suppose I could have said "your 
charger doesn't deliver _anything_ if nothing is connected to it", but 
that wasn't as good, I thought.

Interesting off-topic sidebar: nearly forty years ago I briefly worked 
in the electricity supply industry, where they had (presumably do still) 
things called "current transformers", usually abbreviated to CT, which 
worked counter to how we're used to thinking: they delivered a _current_ 
proportional to the current in the primary (often a "bar primary"!), and 
did so no matter what. They were intended for instrumentation (and thus 
control of course). Unlike conventional power sources, they were quite 
happy to be shorted: they'd deliver their rated current through the 
short. In fact you normally _did_ leave them shorted when not connected 
to anything - because they'd try to deliver that current regardless, and 
if you left them _open_ circuit, would overvoltage and damage 
themselves. I never did figure out how they worked (I don't remember 
trying very hard, I admit. I'm pretty sure they were passive devices 
though - just coils and cores, no electronics). Their advantage was 
that, no matter how long the cable run between them and the (say) meter 
you connected them to (could be many tens of yards - possibly miles I 
think), the current would indicate.
-- 
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.

offensive speech is something to be protected, not celebrated.
- "yoni", 2015-8-5

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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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