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

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I would just like some advice since I melted a USB cable today and I realized I don't have the proper troubleshooting skills.
I bought over a half-dozen "Hype Volt" 6.8Amp USB chargers for stuffing the Christmas stockings:
https://i.imgur.com/Zavgm4B.jpg
I kept one for myself, but, when I used it last night on an iPad and on an Android phone, the iPad lightning cable melted!
When I pulled it off the iPad, it was noticeably extremely hot, but it doesn't seem to have damaged the iPad (AFAIK).
So, I'm just wondering what happened, and, more importantly, when I look at the specs for this device, they don't make sense to me, so, I have difficulty troubleshooting what the problem is/was.
Here are all the specs off the package and off the device: DGL Group Ltd. Hype Volt HV-6PT Model: HC363-5U (also listed as HV-6PT-WHT) Input: AC 110VAC/60Hz - 220VAC/50Hz (800mA max) Output: DC 5V, 6.8A total Maximum Power: 40W Supercharge: 5V@2.4A maximum Universal: 5V@1A maximum
Description: (Amazon.com product link shortened) http://www.walmart.ca/en/ip/hype-volt-68a-wall-adapter-with-5-usb-ports/6000193376994
My questions are varied, because I don't understand how it works, nor how it could have overheated the cable to the tablet.
Here's what it says on the package: "Smart USB Technology: This adapter automatically adjusts power output to fit your charging device. Tablets and e-readers require 2 Amp charging, and this adapter will reroute power to the appropriate USB port you use." "Charging Combinations: - 2 tablets + 3 mobile devices - 1 tablet + 4 mobile devices - 5 mobile devices - 3 tablets"
I am confused about both the pure math and how this operates.
Q1: Since 6.8A times 5VDC is only 34Watts (not 40 Watts), how can they very clearly label it as a 40Watt device?
Q2: How does the device "know" to give tablets 2.4 Amps (12 Watts) but a "mobile device" only 1Amp (5 Watts).
Q3: What if a mobile device "wants" more than 1 amp? Does the charger give more than 1A to the device?
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http://www.powerstream.com/VA-Watts.htm

http://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphone

Ask the manufacturer.
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Scott Lurndal wrote, on Mon, 30 Nov 2015 17:38:04 +0000:

Here is a better (bigger) picture of the unit:
https://i.imgur.com/8bl7ypU.jpg
And a better (bigger) picture of the package:
https://i.imgur.com/30qxupn.jpg
I thank you for the reference, but, after reading it, I don't see how that article helps explain the *output* wattage descrepancy between 6.8A x 5VDC and the stated output spec of 40Watts.
That article explains how to convert Volt-Amps to Watts. "How to convert VA to Watts and KVA to Kilowatts" http://www.powerstream.com/VA-Watts.htm
The input voltage is AC so roughly the input wattage is: 110VAC RMS times 800mA (max) which is roughly 88VA
But it's the OUTPUT wattage that is stated to be 40Watts. 6.8Amps x 5.0VDC is only 34 Watts
Hence, a rather large 15% descrepancy (6 watts less than 40 watts).
I'm sure my math on the output wattage is wrong because the package can't be wrong (that would be illegal), so, I don't see where my math went wrong yet though.
So, any advice is welcome and I will check it out.
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On 30/11/2015 17:55, Danny D. wrote:

No, I don't think it necessarily is, it just rather vaguely says "Maximum power: 40W" on a separate line without any real clue as to what it refers to.

In my experience many Chinese manufacturers wouldn't care about the legality of giving a slightly wrong number. Many lie outright about meeting safety standards.

--

Brian Gregory (in the UK).
To email me please remove all the letter vee from my email address.
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On Fri, 5 Feb 2016 01:39:54 +0000, Brian Gregory

It's what you call (in)efficiency.
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Scott Lurndal wrote, on Mon, 30 Nov 2015 17:38:04 +0000:

Thanks for that article, titled: How USB charging works, or how to avoid blowing up your smartphone
The article explained that USB 3.0 "cables" have 9 wires but when I looked at the 6.8Amp charger, each USB slot seems to have only 4 gold pins on the white protruding tab. I presume the surrounding metal is ground, so, that makes 5 electrical connections that I can see in each USB slot of the 6.8Amp/40Watt "Smart" wall charger.
The article says there are three types of USB 3.0 ports: 1. Standard downstream port (900mA at 5VDC = 4.5Watts) 2. Charging downstream port (1.5A at 5VDC = 7.5Watts) 3. Dedicated charging port (1.5A at 5VDC = 7.5Watts)
The article did say "A regular USB 1.0 or 2.0 socket has four pins", so, I wonder if they counted the ground shield because the sockets on mine only have 4 gold strips on the white protruding tab, so, I'm not sure which USB spec my sockets are.
While this is interesting, after reading that article, I didn't see anything in there that explained the problem nor how to troubleshoot it.
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charging only requires two wires, plus two to negotiate the power.
usb 3 makes *no* difference for a charger.
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nospam wrote, on Mon, 30 Nov 2015 13:42:42 -0500:

Thanks.
That explains why each USB socket only has four gold pins on the white protruding tab.
I did call the company in Edison NJ at 718-499-1000, and, after going through their operator, I spoke with "Bob", a salesman at the office.
I told him, nicely, that it must be true, otherwise it would seem to me to be illegal to over represent the output power by 15%.
He didn't know the answer to why it says it outputs 40Watts but at the same time it says the maximum is 6.8Amps at 5VDC, but Bob said he'd try to find out and for me to call him back tomorrow.
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Bob F wrote, on Mon, 30 Nov 2015 11:43:06 -0800:

This is true that the package says "maximum power 40W" which "could" be input power (but nobody cares about input power - so why would they list it)?
https://i.imgur.com/30qxupn.jpg
The unit says the input is 100-240V at 800mA maximum, but that doesn't calculate anywhere near 40 Watts.
https://i.imgur.com/8bl7ypU.jpg
100 volts (RMS) times 800mA is about 80 VA (aka Watts).
So, if the 40 Watts is input power, it's under reported by 50% at 80 Watts actual.
If the 40 Watts is output power, it's over reported by 15% at 34 Watts actual.
I don't think it's input wattage though, because that would be reported in volt-amperes anyway (VA).
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On 30/11/2015 19:46, Danny D. wrote:

They could give specify VA, watts or both. Whatever they felt like putting in the spec. The VA figure can be higher than the wattage if the current draw in from the mains supply isn't in phase with the voltage.
--

Brian Gregory (in the UK).
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Scott Lurndal wrote, on Mon, 30 Nov 2015 17:38:04 +0000:

Here are some more specs: https://www.touchofmodern.com/sales/hype-volt/smart-adapter
The manufacturer is listed as "DLG Group LTD" on the package:
https://i.imgur.com/30qxupn.jpg
And, as "Hype Volt" on the device:
https://i.imgur.com/8bl7ypU.jpg
Looking for a phone number, I find this description which says they're based out of "Edision, New Jersey" (with the USPTO giving the HYPE VOLT trademark serial number of 86138884 which was subsequently "abandoned"): http://www.trademarkia.com/hype-volt-86138884.html
The contact was provided as: URI DALLAL PO BOX 340256 BROOKLYN, NY 11234-0256
Googling further, the DGL Group seems to be located here: http://listings.findthecompany.com/l/8916005/DGL-Group-Ltd-in-Edison-NJ 195 Raritan Center Pkwy Edison, New Jersey 08837-3650 (718) 499-1000 http://www.dglusa.com
Another phone number was listed here: https://start.cortera.com/company/research/l3r0pul5p/dgl-group/ 195 RARITAN CENTER PKWY EDISON, NJ 08837-3650 | view map (732) 692-5000 www.dglusa.com
Another site gives similar information: http://www.yellowpages.com/edison-nj/mip/dgl-group-468058349 195 Raritan Center Pkwy, Edison, NJ 08837 (732) 379-6000 Primary Phone: (732) 225-1251 Phone: (732) 225-1251
This gives another number: https://www.dandb.com/businessdirectory/dglgroupltd-edison-nj-14169289.html 195 RARITAN CENTER PKWY EDISON, NJ 08837 Get Directions (718) 499-1000, www.dglusa.com
I'm calling them, as we speak.
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was it an mfi-compliant cable or a noname one?

probably not.

from what you've said, it doesn't work.

probably what it consumes, not what it outputs.

usb devices initially get 100ma and then request how much power they really want. the charger responds with how much it can supply.
some non-compliant devices ignore the negotiation phase and either output whatever power is needed and/or the device uses whatever is available. that's probably the case here. however, that alone is not a problem.
an easy way to think about this is a lightbulb. if you screw in a 15w bulb, it will use 15w. if you screw in a 60w bulb, it will use 60w. with a 200w bulb, it will use 200w. nothing about the light socket or the house wiring has changed. it uses what it needs. a 15w bulb won't be overloaded because the socket *can* supply more power.

a properly designed charger won't because it can't. it tells the device "all you're getting is 1a" and the device says "ok".
a shitty charger might, which can cause it to overheat.
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nospam wrote, on Mon, 30 Nov 2015 12:45:25 -0500:

How would I know by looking at it?
Here is a closeup picture of it:
https://i.imgur.com/Dy37Ek8.jpg
It has a USB symbol and that's about it for markings.
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where did you get it and how much did you pay?
if it's from apple, it's obviously mfi-compliant.
if it's a third party cable, it might be compliant. some are and some aren't. generally, cheaper cables are not compliant. really cheap cables are almost certainly not compliant.
the cable itself might not say but the packaging will. companies like to brag that it's compliant.
non-compliant cables don't always melt. it simply means it doesn't meet apple's standards of quality and construction and may not work properly, notably with syncing (charging usually works but not always).
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nospam wrote, on Mon, 30 Nov 2015 14:27:08 -0500:

I have about a dozen of lightning cables so I don't really know, as I don't save the packages.
But I think this one may have come from Office Depot as it was about $10 and it's slightly more than 3 feet long.
Googling, I find this description: http://www.officedepot.com/a/products/739269/Visiontek-Lightning-to-USB-3020-ChargeSync/
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here's the manufacturer's page: <https://www.visiontek.com/cables-accessories/for-mac/visiontek-lightnin g-to-usb-3-0-2-0-charge-sync-cable-detail.html>
the fact that it says 'full compatibility with ios 7' rather than saying it's 'mfi certified' which would guarantee compatibility no matter what suggests that it's *not* mfi certified.
a cable that's mfi certified would say so, as it's a competitive advantage over generic cables: <http://www.ianker.com/product/A7114011
apple has this to say about how to check the cables: <https://support.apple.com/en-us/HT204566
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nospam wrote, on Mon, 30 Nov 2015 15:09:53 -0500:

Thank you for that reference. It's pretty clear from the white faceplate and the lack of printing on the cable that it's not an Apple cable, but that doesn't mean the cable is bad.
I ran down the iPad today and have it on the same charger with a different USB cable (this one I think was from Staples because it's flat instead of being round). So far it's not getting hot, but I will know by tomorrow.
As for the 40Watt figure, I think it's a lie because I googled for the part number that is printed on the side of the unit:
https://i.imgur.com/8bl7ypU.jpg
Notice that HC363-5U printed on the unit?
Googling for just that, I find the same unit only with a different set of markings, which is listed as being 35Watts, which is closer to the 34 Watts that 6.8 Amps gets us at 5 VDC: (Amazon.com product link shortened) "Hausbell 35W HC363-5U UL Certified (UL No:E310745) Family-Sized USB Wall Charger Plug Smart Charger, Single USB Output 2.4A Max,Output total 6.8A Max,5P-USB Output for Apple and Android Smartphones,Tablets and More(White) by Hausbell, Price:     $59.99 & FREE Shipping"
Here's the same unit, this time for $15: (Amazon.com product link shortened)
Here's another, again listing it as 35Watts: http://www.sportinggoodsoutdoor.com/p/detail/B00ORLR1X2/Pre-sale-promotionHausBell-35W-HC363-5U-UL-Certified-UL-NoE310745-Family-Sized-USB-Wall-Charger-Plug-Smart-ChargerSingle-USB-Output-24A-MaxOutput-total-68A-Max5P-USB-Output-for-Apple-and.html
And another: http://hausbell.net/products/cell-phones-accessories/travel-chargers/family-sized-usb-wall-charger-5p-usb-output-238.html
And another: http://macbookpro.deal2hand.com/review-Hausbell-35W-5-Port-USB-Wall-Charger-UL-Certified-with-Foldable-Plug-for-Apple-and-Android-Smartphones-Table_B00ORLR1X2.html
So, pretty much, the 40Watts is either a bold-faced lie, or it's not the wattage of the output.
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Danny D. wrote:

We have couple iPADs kicking around in the house. I wouldn't use quality unknown anything with iPAD for the danger of damaging the unit. Look for UL, CSA,EU approval Logo on stuffs like that. I have O'scope at least I'd check how clean output they produce EU standard is quite higher than that of UL.

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Tony Hwang wrote, on Mon, 30 Nov 2015 18:00:22 -0700:

They print the UL approval on lighting cables?
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Danny D. wrote:

Good charger is not just putting out certain voltage. Ihas some smarts and as charging progresses it tapers back the current. Regulating output current. El Cheapo charger may charge a device but it can shorten the lie of battery or damage the device. Spend some money and buy some decent product.
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