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USB Charging Question

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#1 primexx


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Posted 16 August 2013 - 20:04

So I have come into possession of a 2.1A Apple charger and have one of these on order as well. There's one thing I want to confirm and one I'm not sure about.


1. As far as I understand it the device will draw as many amps as it needs up to the rated maximum of the charger. There is no problem whatsoever using a high amperage charger on a device that doesn't need that much. Is this correct? I've found a lot of conflicting information by Googling so I just want to double check that there's no problem using high amperage chargers for everything.


2. This I couldn't find anything about. Are *all* USB cables (say, 2.0) able to handle up to 2.1A? Or are only some cables? I don't see any ratings on any of my cables. I currently use one from HTC (for my old phone, Mozart) and another $3 one that I bought for travel. Should I obtain new cables that I'm sure could handle 2.1A? How would I even be able to tell since this doesn't seem to be mentioned anywhere as part of the specs?



#2 Roger H.

Roger H.

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Posted 16 August 2013 - 20:08

1 - Correct. The Device will only pull what it needs. The Charger doesn't "push" power to the device.


2 - Yeah, the cables shouldn't matter much. They may get warm if the copper inside is really thing but beyond that they'll work just fine.

#3 Astra.Xtreme


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Posted 16 August 2013 - 20:31

To answer your question about the current rating, there are NEC standards which all wire must comply by.  The NEC books themselves cost money, but it's pretty easy to find the tables online:




So for this case of a 2.1A rating, the wire should optimally be 18 gauge.  


This is the area where some of those cases of the knock-off cables killing people could be caused by.  If they don't go by the NEC standard, and they don't correctly classify the wire as a "transmission" wire, then the wire may not be able to handle the current, which will short out other components which were also wrongly de-rated. Anyway, I guess that's besides the point. :)


To actually be able to determine if your cable is the correct wire gauge, you'd have to snip through the insulating and measure the copper conductor thickness.  Not exactly convenient though, hah.  As long as it's not a $0.99 cent Chinese knock-off, you shouldn't have anything to worry about.  And I guess you could also tell by whether the wire gets hot.

#4 OP primexx


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Posted 16 August 2013 - 21:49

hmm... it seem rather unlikely though that most USB cables are a little over 1mm... however I don't see any cables advertised as being high amperage.. guess i'll find out if anything gets warm.