A USB has 2 power cables and 2 data ones afaik. If i were to split these and re solder them to make essentially a Y cable with one USB A for power and one for data, and then plug the power into wall and data into PC, would I be able to charge my phone at full speed (2.1A) and be able to do data transfers simultaneously?
3 Answers
A lot of devices use a specific resistances across the data wires to detect whether they are connected to a computer or a wall charger.
A fully compliant USB device will see the normal "data" termination resistors and limit their charge to 500mA, thus making your modification pointless.
Less compliant devices may suck down as much juice as they can and expect the device supplying the power to do the limiting, in that case your modification will work.
Either way though you are potentially doing a bad thing as by having your USB device supplied from a different source it can create a potential difference between the USB power and the data lines. External hard drives have protection and compensation for this, your cable will not. You could be fine, but you could also damage the USB chip in your phone or computer or both.
Or it could be fine, we don't know whether all your devices are plugged into a well grounded mains system, or whether you are going to pass the shield through on both sides of this cable... As a minimum you should pass the ground (-ve) from the PSU to both the source USB port as well as the device being charged.
Only you can justify whether the incredibly minor inconvenience of unplugging your device from a computer to plug it into a proper charger outweighs the possibility of damaging your phone or computer.
I would not do what you are intending mainly because good chargers are never far away, a computer may at least slowly charge a device, and there are some risks with doing it. As always though YMMV and it may just work.
answered Apr 30, 2016 at 17:10
In theory yes, they Sell usb Y cables, no need to make one, They use to include them with usb hard drives in the early days of XP when one usb port would not power the enclosure due to the usb 1.1 power specification, so they added another usb pigtail to use power from the second usb port. I still have one of them.
You could use a y cable even if it does not have the correct end for your phone, just use a usb gender changer adapter.
A better solution is just use this Y cable on the PC, it will pull 500ma for each of the usb 2.0 connections which is 1.0amps.
Doing as you suggest is an experiment and may damage hardware.
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Could I plug one in the wall then and get full 2.1A charging speed. Or do they both need to go in the computer Commented Apr 30, 2016 at 16:49
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2I'm not sure what would happen with 2 separate power sources, since they are on the same wire, it would be an experiment with possible hardware damage. Overall it does not sound like a good idea.– MoabCommented Apr 30, 2016 at 16:51
That could work but it could also damage the computer's port as well as the phone's unless you implement a circuit that would balance them together.
Nothing could guarantee that the voltage and ground would be identical from both power sources.
USB hubs that accept an external power source will use transistors to separate the two circuits.
answered Apr 30, 2016 at 16:46
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There would only be one power source. The computer would provide data and no power, the wall would provide power and obviously no data Commented Apr 30, 2016 at 16:48
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2How do you think electronic devices identify bits? It's always relative to the common ground which wouldn't be the case here. Commented Apr 30, 2016 at 16:49
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@HamzahMalik The data wires are both “+”. If you disconnect the ground, the connection won’t work, even though both devices are active.– Daniel BCommented Apr 30, 2016 at 17:21