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I am still searching for a solution to conveniently power some external hard drivers.

I would like to use only one AC plug as I think it is not very efficient to use two different PSUs.

My idea is to split the cable from a 2.6A power supply. (actually I did not find a 2.7A one)

AC mains -> 5V 2,6A PSU --> USB micro plug -> Raspberry Pi (Model B)
                         \                         | USB data
                          \--> round DC plug -> powered USB Hub

So this is more an electrical engineering question: Is it okay to connect the 2.6A input to raspberry Pi and to the USB hub parallely? Could there any overloading happen?

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2 Answers 2

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Your config is good but i think is easier to make a ring!

RasPi USB --> Hub-USB --> RasPi MicroUsb power

Both solutions have the problem of groundloop

You can avoid it by stripping the ground in the last connection:

Hub-USB --> RasPi MicroUsb power

or in your connection schema:

RasPi USB --> Hub-USB

2A power adapter is enough: i tested it with 2 USB self powered hdd, a wifi adapter and a usb lan adapter

NOTE that this works only with version B

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  • But the USB hub would supply max 500mA per port - RasPi needs 700mA - how does that work?
    – Alex
    Mar 27, 2013 at 9:08
  • @Alex hubs usb are dumber than you think. anyway as I said I tested this configuration. I also measured raspi B current for a day and it need 450mA if you use a powered hud with all usb device attached. I think they write 700 including usb devices
    – giammin
    Mar 27, 2013 at 9:54
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    @Alex: 500mA should actually be enough for RasPi itself since all the other devices are powered by active hub. I also use the same setup and it works fine. All you have to remember is that you now can't disconnect microUSB cable to turn RasPi off, you have to disconnect the HUB.
    – Krzysztof Adamski
    Mar 27, 2013 at 9:59
  • @giammin: What do you mean by striping the ground?
    – Krzysztof Adamski
    Mar 27, 2013 at 10:02
  • @KrzysztofAdamski it is better to avoid groundloop. it is enought to remove the ground from the cable that power raspi from hubusb. in this way the usb ground is not looped
    – giammin
    Mar 27, 2013 at 10:12
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I found a USB hub: "Plugable USB 2.0 4 Port Hub / BC1.1 Charging. It came with 2.5A @ 5V power supply. The BC means Battery Charger - has the power to charge an IPAD via USB without being connected to computer. Also has the needed up-link cable (2ft USB A to USB mini A)

I got USB A to USB Micro-B 6" cable to power RPi. Then hooked the RPi to the up-link port. With the setup, I power the PI and still have 3 ports open, That have Wireless NIC and 16GB Memory stick and a port left over for a disk drive from time to time. Since my unit is model B, the second USB port has a wireless keyboard/mouse.

Does look a little funny with USB cables entering both ends of RPi, but work very nicely.

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