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Do you need a special USB cable for 2 amp charging?

amigo108 362 65 September 11, 2013 at 07:05 AM
I have a question about the USB cables. Are all micro USB cables capable of carrying 2.1 amp at .5v or do you need one spec'd for that? My guess is that the wall charger, or cigarette lighter adapter is what dictates how much juice is supplied and how fast, but I just wanted to know if the USB cable can also be a limiting factor. Also, is there a difference between charging off the computer using a USB 3.0 port vs standard USB port?

I've got a bunch of AC/USB wall plugs (mini-bricks? not sure what they're called) from my old palm pre phones as well as from nooks and galaxy note 2, and was wondering if I can use any old cables with them and get the faster charging or if I have to be careful not to get the good cables mixed up with cheap ones from other devices?

Thanks

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#2
Cables can be a limiting factor. I definitely keep my good ones separate.

The official power specifications for USB are as follows:
USB 2 - 500mA
USB 3.0 - 900mA

However, many implementations offer more power than that.
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#3
Quote from hbarnwheeler View Post :
Cables can be a limiting factor. I definitely keep my good ones separate.

The official power specifications for USB are as follows:
USB 2 - 500mA
USB 3.0 - 900mA

However, many implementations offer more power than that.
that's what i was afraid of. Sadly, there's nothing listed on the cables themselves, i remember what some of the good ones look like but not all.
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#4
Quote from amigo108 View Post :
that's what i was afraid of. Sadly, there's nothing listed on the cables themselves, i remember what some of the good ones look like but not all.
Yeah, the problem isn't that there are different types of cables (for different power contexts) but rather just that some of the super cheap ones just aren't very good quality and so don't perform as well.
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#5
Quote from amigo108 View Post :
that's what i was afraid of. Sadly, there's nothing listed on the cables themselves, i remember what some of the good ones look like but not all.
Are not all USB 3.0 type A cable connectors end blue and USB 2.0 white?
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#6
Quote from repitall View Post :
Are not all USB 3.0 type A cable connectors end blue and USB 2.0 white?
The power specifications I mentioned above for USB are for the ports, not the cables, though it may be true that usb 3 cables are somehow able to carry more current than a similar quality usb 2 cable, though I doubt it.

OP, this app [google.com] may be able to help you out, if you have an android device which will report current information.
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#7
This should be easy to estimate.

A Monoprice USB cable [monoprice.com]has 28 awg conductors in it. 28 awg is rated for 1.4/0.22 A (VAC) according to here [powerstream.com]. Those numbers are for chassis wiring and power supply (respectively).

I am not an electrical engineer, so the AC/DC question (does it matter if 120VAC or 5VDC?) I googled and apparently current is current [allaboutcircuits.com].

If we use the higher of the two numbers above, the minimum AWG acceptable for 2.1A is about 26 AWG (2.2/0.361). I'd have to believe we look at the left number as we don't get to 2.1 on the right number until 18 AWG and for USB that'd be one huge ass cable!

Looking at a USB 3.0 cable [monoprice.com], it's listed as 28/24 AWG - which is likely a difference between the number of required conductors in 3.0 (9 vs 5?).

At any rate, you can buy a heavier gauge USB2 wire (I couldn't find info on AWG in MP's "premium" cables), butthese are the ones [amazon.com] I use for all my devices.
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#8
To truly know you'd have to know the wire gauge and then look up an electricians table to see what the ampacity is.
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#9
Another factor is the manufacture. Doesn't samsung ground one of the data pins to do 2 amp charging?
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Vague questions receive vague answers . . . . . .
#10
i wanted to know the same question.


can someone show me a usb cable, that i can use for 2.1amp?
ebay link/amazon appreciated. (even if its from china thats ok).
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#11
Lets clarify a few things...
-Current is current regardless of if it's AC or DC.
-Most reasonably high quality usb cables work fine at 2.1A
-If the cable specifies wire gauge, a smaller AWG number equates to a larger cable and larger current carrying capacity.
-consulting "electrician" tables isn't going to be particularly helpful or relevant. They generally don't go low enough in current to be relevant, are based on much longer runs of wire, and are fairly conservative.
-the shorter a cable of give wire gauge is, the more current it can carry.
-Don't expect wonders from a cable that costs $0.99

-If the cable feels warm, when charging you should replace it / replace it with a better cable. Cables that have developed breaks in some of the wires are more likely to get warm as a result of reduced current capacity. A poorly constructed or undersized cable could also get warm
-Newer rapid chargers use low voltage AC instead of lower voltage DC (5V) which allows similarly sized cables and connectors to carry more power. Eg. 5VDC*2A = 10W, 30VAC*1A = 30W
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#12
Quote from jkee View Post :
Lets clarify a few things...
-Current is current regardless of if it's AC or DC.
-Most reasonably high quality usb cables work fine at 2.1A
-If the cable specifies wire gauge, a smaller AWG number equates to a larger cable and larger current carrying capacity.
-consulting "electrician" tables isn't going to be particularly helpful or relevant. They generally don't go low enough in current to be relevant, are based on much longer runs of wire, and are fairly conservative.
-the shorter a cable of give wire gauge is, the more current it can carry.
-Don't expect wonders from a cable that costs $0.99

-If the cable feels warm, when charging you should replace it / replace it with a better cable. Cables that have developed breaks in some of the wires are more likely to get warm as a result of reduced current capacity. A poorly constructed or undersized cable could also get warm
-Newer rapid chargers use low voltage AC instead of lower voltage DC (5V) which allows similarly sized cables and connectors to carry more power. Eg. 5VDC*2A = 10W, 30VAC*1A = 30W

I see I replied earlier but anecdotally, all my android stuff charges at 2.1A; I never pay attention to the cables used (meaning I don't only use certain cables for this); I've never had a problem with any of the cables and I've never had any of them even become warm. This includes the OEM cables (Samsung), the higher-rated Amazon cables (see my link, but I've bought 3-4 different ones) and the cheapo ones that come with some Chinese devices.

I really think this is getting way too analytical.
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#13
Quote from Dr. J View Post :
I really think this is getting way too analytical.
Yeah, you're right. > 90% of all USB cables made today are probably fine. That said, there are some REALLY crappy cables out there. I got one with a surge protector that had a usb port a few years a go that's about as big around as a piece of raw thin spaghetti. I've also seen some scary cables at the dollar store. There are however plenty of good cables for <$5.

The usb-c / usb power delivery spec can deliver up to 100W of power. For this type of application you certainly want to be careful when selecting chargers and cables.
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#14
Quote from jkee View Post :
Lets clarify a few things...
-Current is current regardless of if it's AC or DC.
-Most reasonably high quality usb cables work fine at 2.1A
-If the cable specifies wire gauge, a smaller AWG number equates to a larger cable and larger current carrying capacity.
-consulting "electrician" tables isn't going to be particularly helpful or relevant. They generally don't go low enough in current to be relevant, are based on much longer runs of wire, and are fairly conservative.
-the shorter a cable of give wire gauge is, the more current it can carry.
-Don't expect wonders from a cable that costs $0.99

-If the cable feels warm, when charging you should replace it / replace it with a better cable. Cables that have developed breaks in some of the wires are more likely to get warm as a result of reduced current capacity. A poorly constructed or undersized cable could also get warm
-Newer rapid chargers use low voltage AC instead of lower voltage DC (5V) which allows similarly sized cables and connectors to carry more power. Eg. 5VDC*2A = 10W, 30VAC*1A = 30W
Looking at a published old school electricians table likely won't yield much information for those higher AWG sizes, but they definitely publish them online. I think the bigger issue is figuring out what the AWG size is in the cable you have/buy/intend to buy. If your charge wire is any smaller than 24 AWG I'd be a little concerned.

They do sell 24/28 AWG micro USB cables, monoprice has some. http://www.monoprice.com/Search/I...+usb+24AWG
In this case the power wire is 24AWG and the data wire is 28AWG. I would not trust a cheap no brand china cable to have 24AWG power wires.
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Last edited by brbubba August 10, 2015 at 07:42 AM
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#15
Quote from Dr. J View Post :
I see I replied earlier but anecdotally, all my android stuff charges at 2.1A; I never pay attention to the cables used (meaning I don't only use certain cables for this); I've never had a problem with any of the cables and I've never had any of them even become warm. This includes the OEM cables (Samsung), the higher-rated Amazon cables (see my link, but I've bought 3-4 different ones) and the cheapo ones that come with some Chinese devices.

I really think this is getting way too analytical.
Talk about bump

Gauge of the cable does matter. The 28/24 gauge cables are what you want. Especially if it's longer. The really cheap cables usually use a thinner gauge and are not able to carry as much current. Now this all kind of changes with the Qualcom quickcharge stuff. thinner gauge cables are ok, but your still best with a 28/24.
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