Advice sought on why 6.8A USB charger melted USB cable today

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nospam wrote, on Mon, 07 Dec 2015 12:35:48 -0500:

I'm perfectly happy if I'm wrong because that would mean that I learn something, as long as we can explain why I'm wrong.

I am well aware that current is not "shoved" into a device that doesn't "draw" (or "sink") that current.
I realize that the current "sourced" by the charger is whatever the device "sinks", up to the maximum point that the charger is able to "source".
However, what's "smart" about this charger is that it can "source" 2.4 Amps (or so it says) from each port up to a limit of 6.8 amps.
So, if you plug in three devices, two of which are tablets sinking 2.1 Amps, while the third is a phone sinking only 1.0 Amps, then the device will "choose" which ports to source the 2.1 Amps and which ports to source the 1.0 Amps.
I do understand you now in that you're saying that the device "asks" (so to speak) for whatever amps "it" wants to sink, and the charger just blindly supplies that (or it doesn't) when it's an Apple charger.
What you're saying, I think, is that this charger just as blindly does that too, but in the case of this charger, you don't have to choose a low-power (1 Amp) port and a high power (2.4Amp) port because the charger will choose which port to source the 2.4 Amps and which ports to source the 1.0 Amps.
I'm not sure what the smart charger does when I plug in 3 tablets, all "asking" to sink 2.4 Amps though.
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it's been explained several times.

then you should be aware that there cannot be smarts in the charger. it's a +5vdc power source.

no.

no it won't. it has a dedicated 'superport' with 2a and the rest are 1a.

nope.
stop twisting and lying. it's really obnoxious.

nope. the specs said there's one superport.

two will get 1a.
regardless, there are no smarts in the charger for eoc detection. it just supplies power. the smarts and eoc detection are in the device and/or battery.
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nospam wrote, on Mon, 07 Dec 2015 19:12:07 -0500:

There are two so-called 'superports'. And they float to any two ports. Why can't you see this?
You are right though, that the eoc isn't detected by the charger.
The sink current is detected, and that floats the two superports. That's the smart part.
It doesn't detect EOC. That's the dumb part.
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that's minor.

there's no way for that to happen with a usb charger.
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Danny D. wrote:

You shouldn't be using marketing copy to understand technical details.
<snip>

How do you define smart? You should also learn some basic circuit theory.

Try reading the USB specifications regarding charging.
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joe wrote, on Mon, 07 Dec 2015 14:35:39 -0600:

The way I define it is that the charger is smart enough to know how to shunt current to where it's needed without me having to do that myself.
I plug in whatever I want to plug in (within the defined limits). And the charger shunts the current to those devices accordingly.
For example.
If I plug in five devices which each "ask" to sink 1 amp of current, then the charger is smart enough to make available a shunt of up to 1 amp each source current into those five sink devices.
Likewise, if I plug in three devices where one asks for 2.0 Amps, and another asks for 1.6 amps and another device asks for 1.4 amps, then the charger is smart enough to shunt 2.0 amps into one, 1.6amps into the other, and 1.4 amps into the third, for a total of 5.0 Amps (or 25 Watts).
With many multi-port chargers, one port is a *dedicated* 2.1 Amp (max) port while the other is a *dedicated* 1.0Amp (max) port.
This charger is "smart" in that the dedication is switched between the ports (i.e., they're not all 2.4Amp ports, but any one or two can be depending on what you plug into it).
That's smart.
But maybe I misunderstand since you people are telling me otherwise.
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not really and it doesn't work the way you think it does either.

yep.
a smart charger means it intelligently charges a battery by constantly monitoring its state of charge and changing the charge strategy as needed. usb chargers do *not* do that.
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You are wrong.

The 'reroute' power is the 'smart' part of the charger. Most USB chargers only supply 1amp to the USB port. Some chargers supply 2.1 amps. However, supplying 2.1amps to 6 ports is a LOT of power, so most chargers will designate one or two 2.1Amp ports.
This charger (and a lot of newer chargers) have some smarts that allow them to route those two amps to whichever ports need them. In this case, up to three ports.

This rerouting of which ports can provide 2amps has nothing to do with the complicated software on the devices and batteries.
--
> I miss the old days. I haven't killed anyone in years.

That's sad.
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Lewis wrote, on Tue, 08 Dec 2015 13:57:35 +0000:

I do understand that the "smarts" in the charger is simply for re-routing the "superport" to up to three ports.
The "dumb" part of the charger is that it does not sense the EOC of the battery. Those smarts are in the device/battery circuitry itself.
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More than you might think!
I came across this recently:
http://www.righto.com/2015/11/macbook-charger-teardown-surprising.html
--
Cheers,
Daniel.
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the smartness in that charger is for communicating with the laptop about the adapter's capabilities, not charging strategies, which is handled by the macbook based on the reported capabilities.
a magsafe charger tells the macbook its maximum power and the macbook budgets it appropriately. if the adapter has less power than what was originally supplied, the macbook will charge at a reduced rate or even not at all, depending on how much power is actually available and what the macbook needs.
in any event, the thread is about a usb charger which doesn't do any of that. it outputs 5vdc, hopefully compliant with the usb charging spec (some noname crap is not).
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Yes, of course. We've all been using (relatively) dumb chargers for years so it's pretty obvious that a wall-wart doesn't *need* to have the smarts of a 128k Mac!
The point was being made (by Bruce Sinclair, to whom I was replying) that modern chargers do have some smarts, and I thought it might be interesting to give an example (as I'd just come across it recently and had the link to hand) of a charger with a very great deal more smarts than one might imagine.
It *is* slightly boggling just how smart a charger can be, while remaining roughly plug-sized.

Indeed, but threads drift ... it would be a dull world if they didn't.
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Daniel.
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it doesn't.

some do, but not for charging strategies.
the magsafe adapter example you cited is for magsafe communication so that the laptop knows how much power is available.
for usb chargers, that's done over usb.
it doesn't communicate soc or eoc. that's in the device itself and/or the battery.

not really. there are much smaller products that are quite a bit smarter than any charger.
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nonsense. 1 amp through a coiled usb cable is not going to heat up. they even make coiled usb cables.
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Correction - I never made that point. :) (snip)
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Yep. If you don't know this, you work it out when you plug in a coiled cable for a while and it gets hot. :) Power cables on rolls have always come with the 'completely unroll before using' (or similar) instructions. :)
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wrote:

it's better to not fail in the first place.
nothing is perfect, but buying a reputable brand which is known for reliability is the best way to minimize how often you have to go back to get something fixed.
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True. :)

In theory, that's true. What I recall of electronics brands reliabilities however, is that there is actually little in it.
In theory, theory and practice are the same. In practice, they are not. :)
Personal experience with scientific equipment these days suggests that the smarter something tries to be, the more often it will fail. MTBF I guess ... the more bits, the more broken bits. :)
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Bruce Sinclair wrote:

I am a class of '60 in EE. Started with vacuum tubes all the way to nano-tech in electronics engineering. MTBF has been improving steady over the years. Just have a field trip to a big manufacturing plant and see how QC engineers are screening components for their product. Very serious affair. Even here you get what you pay for. For an example, mil-spec laptops cost few times more than consumer grade. You figure out why! Once back in '70s I witnessed testing mil-spec DEC PDP8 mini computer. From chopper up 3500 ft. it was tossed down, it did not suffer damage. Commercial grade PDP8 would be in pieces scattered all over. Another example, look at Panasonic Toughbook, ever tried one of those? You can run over it with your car without any problem. I always try to buy prosumer level product when I need something.
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Tony Hwang wrote:

And look at today's cars, they are like more electronics than mechanics. Drive one like 2013 onward? Some Runs by wire like air planes(CAN buss)
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