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I dont really know much about electronics and I tried to seach online if this specific thing im thinking of doing has ever been posted and i cant find anything exactly the same.

So what im trying to do is make a makeshift powered usb hub. Ive seen several online but they are made differently. Basically, i wish to just connect the data + and - from the computer to the hub, disconnect vcc and gnd from the computer by cutting the ends of those wires coming from the pc, and finally connect a 5v 2a power supply from a tablet charger to the hub vcc and gnd.

Is this viable? I just thought this could be cool because since only the charger's power is connected to the hub, i wont need a diode since there is no possibility that voltage will be sent to the computer as that line is cut. Will this allow the pc to send data to the hub?

I hope this is not a dumb question. Thanks in advance!

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  • \$\begingroup\$ You will, at least, have to connect the grounds otherwise the data lines won't have a reference to work from. \$\endgroup\$ – Transistor Jul 6 at 13:20
  • \$\begingroup\$ Noted. Thanks for the answer! \$\endgroup\$ – Evan777 Jul 6 at 13:28
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Will this allow the pc to send data to the hub?

Not if you connect the tablet...

Reason behind this: The hub still identifies itself as being bus-powered, and thus the charging current of the tablet -reported via USB- would (probably) be above the (100/400mA) limit for bus-powered USB hubs. In this case the host os will complain with an error message and not allow you to transfer data.

Alternatively the tablet might use a rather low current over USB in data mode, that usually discharges the battery (at least with the screen turned on).

It is not possible to fast charge a tablet and use USB in data mode, because the data lines are used to recognize the fast charging capable USB power source.

USB-C finally changed that - but both tablet and hub/PC must use this port type.

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  • \$\begingroup\$ I think thats ok, I wont be connecting a tablet to the hub. The tablet pc charger is just a spare one i had lying around, and the hub will just be uaed to power a keyboard , mouse, and a wifi adapter. The problem was my pc's usb (also a tablet, it just has one usb port) cant power all three devices at the same time, and thats why i planned on making the hub powered. Thanks! \$\endgroup\$ – Evan777 Jul 7 at 3:34
  • \$\begingroup\$ Same effect: The USB host will add the requested currents, see that the sum is too big and complain to you - and prevent usage of the devices. You will need a hub that properly tells the host that it is self-powered. \$\endgroup\$ – Turbo J Jul 7 at 15:19
  • \$\begingroup\$ There are very few bus-powered (aka "mobile") hubs that identify themselves as "bus powered". 99% of these hubs would lie in descriptors as being "self-powered". It should be easy to determine using USBTreeView tool. superuser.com/a/1181052/620011 \$\endgroup\$ – Ale..chenski Jul 7 at 17:28

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