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

394 69 September 11, 2013 at 07:05 AM in Tech & Electronics (3)
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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Joined Aug 2008
L99: Slicker than Ice
> bubble2 6,537 Posts
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slapshot136
08-10-2015 at 11:40 AM.
08-10-2015 at 11:40 AM.
It's about how much power is wasted in the cable vs what reaches your phone - longer cables will waste more, and thinner cables will also waste more - best way would be to measure power into the cable and power out of the cable, but outside of that, thicker gauge cables are better. Either way, both cables will support 2 amps of current (although the thinner gauges like 28 might not be able to support that level 24x7, it will last long enough to charge a phone and thus reduce the current down to a level that it can support)

also, while current is current, a cable rated for Y amps of AC will be rated significantly lower than Y for DC, because when rating wires it's more about the average current vs the peak current, and the average current is the same as the peak current for DC, but not for AC.
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Joined Jun 2005
Let Sleeping Dogs Lie
> bubble2 8,770 Posts
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komondor
08-10-2015 at 01:51 PM.
08-10-2015 at 01:51 PM.
If you want something you can depend on get a "FAST" charger with a cable the one that came with my Note 4 will work with some cables I have and some will not, they charge but not FAST charge.
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Joined Sep 2006
L10: Grand Master
> bubble2 10,138 Posts
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larrymoencurly
08-12-2015 at 01:00 PM.
08-12-2015 at 01:00 PM.
This table about wire gauge versus resistance and maximum amp capacity [powerstream.com] says #28 wire shouldn't be used for more than 1.4 amps for chassis wiring, which probably means roughly a couple of feet at most, and the resistance is 0.0649 ohm per foot, which will drop about 1/2 volt at 2 amps for a 4 foot long cable. Make that about 1.0 volt if the ground shield isn't connected to power ground. I'm not sure if most USB cables are even #28.

Lithium batteries are so particular about charging needs that devices have battery charger circuits inside to control the charging, so you probably don't need exactly 5.0 volts coming into them from the USB port. OTOH they may not do anything to limit the current they draw, so if they take more than the
5 volt source can put out, they may overload it.

USB 3.0 ports are supposed to have a capacity of at least 0.9 amp, compared to 0.5 amp for USB 2 and USB 1.
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