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I have 8A 6port usb charger. It has two ports marked as fast charing, and the phone here actually charges faster than in the two other ports. When I dismantled it, all the USBs were on the same power line, so the charger is definitely somehow telling the phone how much current can it use. There are bunch of resistors around the ports, looks like connected to the data pins, but I will have to desolder the USB's to see how they are connected, as most of the paths are on the PCB covered by the ports. I would like to be able to make the third port also fast charge (don't worry, I know there are current limitations and the other ports are used for handsfree and smartwatch cahrging which takes ~500mA, and as the phones draws ~2A, it will still be in the power source's limits). I tried to find a schematics for the resistors connections, but only thing I was able to find is about how it's done for Apple and tons of articles about quickcharge with no tech specs.

Only thing I need is to tell Android phone it could draw more than 1A from the USB. I'm also going to build charging station from PSU (5V 30A) and here I would also want to tell the phones that they could draw more power. Thanks for any help.

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    \$\begingroup\$ The wiring (including circuit board traces) might be heavier for the fast charging ports... much better to put your high current draw devices on the high current ports than try to trick them. \$\endgroup\$
    – Ben Voigt
    Feb 16, 2017 at 22:29
  • \$\begingroup\$ This is a duplicate of electronics.stackexchange.com/q/123172/117785 \$\endgroup\$
    – Ale..chenski
    Feb 17, 2017 at 18:35

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The standard USB qualified method for telling a phone that it can fast charge is to short the D+ and D- lines together. (USB calls this out in its documentation)

The non standard way is to place voltages on the data lines.

schematic

simulate this circuit – Schematic created using CircuitLab

The usual way this is done is using two resistor dividers. What is unfortunate is that these voltages are all different depending on your device. If your chargers is capable of fast charging your phone then measure the voltages on the data pins and set up your own dividers to get those same voltages.

ePanorama had a great aggregation of the information on fast charging USB ports as it related to Apple devices. This APC article discusses the variation in D-/D+ voltages used by various manufacturers.

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  • \$\begingroup\$ Do I unerstand right that shorting D+ and D- works for everything, but placing resistors to them (which costs more) doesn't always works? If so, why are chargers I bought from eBay using the resistor method it it doesn't always works? \$\endgroup\$
    – Adam Ježek
    Feb 16, 2017 at 23:03
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    \$\begingroup\$ @AdamJežek No, you have that wrong. USB consortium made a standard that shorting the data pins together means fast charging. About half to three quarter of OEMs use it. The rest roll their own. This is why i suggested measuring the voltages and reproducing them on the other port. It sounds like your phone falls into the "roll their own" category. You could try bridging the data pins together with a bit of solder to see if your phone likes it. My phone will fast charge from both an iphone charger or from shorted data pins. \$\endgroup\$
    – vini_i
    Feb 16, 2017 at 23:12
  • \$\begingroup\$ I have Samsung Galaxy, but I would like to to bude usefull for more. Is there any list of manufacturers where could I find if they use shorted/which voltage, or do I have to use the trial-error method? \$\endgroup\$
    – Adam Ježek
    Feb 16, 2017 at 23:29
  • \$\begingroup\$ @AdamJežek I wish there was such a list. Trial and error is about the only way right now. \$\endgroup\$
    – vini_i
    Feb 16, 2017 at 23:31
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    \$\begingroup\$ Here is a list of what different chargers use on D+/D-: electronics.stackexchange.com/a/271681/117785 \$\endgroup\$
    – Ale..chenski
    Feb 17, 2017 at 18:49
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If your charger is indeed quick charge capable, go to Qualcomm and read up on QC. It. Is a lot more involved than being able to do the with a few resistors.

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    \$\begingroup\$ Question is about fast charging, not QuickCharge (TM). \$\endgroup\$
    – Ben Voigt
    Feb 16, 2017 at 22:27
  • \$\begingroup\$ @ben doesn't mean OP might not be mistaken or didn't know it was QC or something \$\endgroup\$
    – Passerby
    Feb 16, 2017 at 23:29
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    \$\begingroup\$ Quick Charge is, I would say, pretty new technology and still many phones, including mine, doesn't support it, there is only fast charge. \$\endgroup\$
    – Adam Ježek
    Feb 16, 2017 at 23:31

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