Power on the Raspberry Pi is a tricky business. I think on the B+ they've made it easier to deal with but it still cannot pass through a lot of current. So a powered hub is necessary, as previous posters mentioned.
It does indeed backfeed into the Pi. I used thin stripes of electrical tape to cover the outer two contacts within the USB connector of the cable that connects the Pi to the hub, and that took care of that problem. Also, I found out that my hub (a cheap piece bought from DX), even when externally powered, would draw some current from the Pi during load. So the electrical tape took care of that too. If you have a good power supply for the hub you can power your Pi from the hub itself with an additional cable (i.e. the hub will be connected to the Pi twice, once with a USB A-B cable like any hub, and once with a USB A - MicroUSB B, from one of the hub's ports into the Pi's power supply port). This removes the need for a second power supply. One problem that I faced, though, was that a wifi dongle connected to the hub was being disconnected and reconnected every few minutes. I plugged it directly into the Pi itself and it works flawlessly. I still don't know why that problem happened; after all, they both are on the same power supply (the hub's). Other devices on this hub (the Pi itself as well as other stuff) seem to work fine. Maybe the hub's power supply is noisy and the Pi filters it when it passes it through. No idea. Alex On Wed, Dec 17, 2014 at 4:12 PM, Moish <mo...@mln.co.il> wrote: > > > On 17/12/2014 16:03, Gabor Szabo wrote: > >> I've got this one: >> http://www.dynamode.com/english/pages/product/Datacom% >> 20Products/USB%20Products/USB-H40-A2-0.html >> >> when I connected this device to the Raspberry I got these message >> >> Dec 17 13:59:48 pi kernel: [246075.608736] usb 1-1.4: new high-speed USB >> device number 112 using dwc_otg >> >> Dec 17 13:59:48 pi kernel: [246075.710412] usb 1-1.4: New USB device >> found, idVendor=05e3, idProduct=0608 >> >> Dec 17 13:59:48 pi kernel: [246075.710447] usb 1-1.4: New USB device >> strings: Mfr=0, Product=1, SerialNumber=0 >> >> Dec 17 13:59:48 pi kernel: [246075.710462] usb 1-1.4: Product: USB2.0 Hub >> >> Dec 17 13:59:48 pi kernel: [246075.721467] hub 1-1.4:1.0: USB hub found >> >> Dec 17 13:59:48 pi kernel: [246075.721944] hub 1-1.4:1.0: 4 ports detected >> >> >> When I connected the HD to it the syslog was filled with this message: >> >> hub 1-1:1.0: over-current change on port 2 >> >> but I still could not see it using sudo fdisk -l >> >> Gabor >> >> >> It will work only with low energy consumption devices. > See previous messages regarding usb hubs with external power supply. > Moish > > > _______________________________________________ > Linux-il mailing list > Linux-il@cs.huji.ac.il > http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il >
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