A loaded Raspberry Pi model B sucks down about 700-750mA, or more if you've hooked up particularly current-hungry USB devices to it. The USB specification states that USB devices should demand no more than 500mA, and many computer sockets/hubs will automatically disconnect devices that suck down more power than this - especially if the device doesn't do proper USB power negotiation. Some cheaper USB hubs (and some more expensive ones too) don't have per-socket regulation so you can suck the full 2A (or whatever they provide) out of just one, but I would not recommend it as a long term solution - the Pi is notoriously unstable when it's not connected to a decent power supply. Many computers provide more than 500mA per socket, but this cannot be relied upon.
Some USB hubs deliberately have a high current port - these are normally highlighted for charging iPads and the like. Otherwise standard tablet/phone chargers that plug into the wall work quite well - I'd advise checking that these provide at least 800mA before using it. I'm using a 2.1A Nexus 7 charger for my RPi and it works wonderfully.
Hope this helps,
Benjie.
On 5 Feb 2013, at 10:59, "Chris. Aubrey-Smith" <cas194@???> wrote:
>
>
> On 5 February 2013 09:44, Paul Tansom <paul@???> wrote:
> ** Dr A. J. Trickett <adam.trickett@???> [2013-02-04 20:22]:
> > Having actually seen and photographed a Raspberry Pi I think I'm sold on the
> > idea of them. I currently have an Ethernet switch under the TV, spare power
> > and a CRT (composite TV input) though I do plan to replace it with a flat TV
> > of some sorts eventually (HDMI input).
> >
> > It seems to make sense that a RPi Model B makes sense, it would be small,
> > silent and fun - it appeals to my inner geek. I've a few questions:
> >
> > 1) Where is the best place to get one? Maplin or Farnell or RS?
> >
> > 2) What else does it need?
> > An SD card for the OS and local storage
> > A case
> > A USB power supply
> > A USB keyboard and mouse if you want to drive it directly
> ** end quote [Dr A. J. Trickett]
>
> I've been keeping a careful check on costs: (lifted from a spreadsheet)
>
> Raspberry Pi Costs
> ---------------------------
>
> No. Item Cost Notes
>
> 1 Model 'B' Hardware Kit £33.89
> 2 Pre-loaded 16Gb SD Card £13.99
> 3 Wireless LAN USB Plug £9.99
> 4 User Guide £9.09
> 5 Case £5.65
> 6 Power Supply £4.99 *Could be powered via USB
> 7 USB Adapter for Keyboard £0.00 (From stock)
> 8 HDMI Display Cable £0.00 (From stock)
> 9 USB Hub £0.00 (From stock)
> 10 Display £0.00 (From stock)
> 11 Keyboard (PS2 Plug) £0.00 (From stock)
> 12 Mouse £0.00 (From stock)
>
> Incidentally, if you have a powered USB hub, the R-Pi doesn't need a separate power supply.
>
> I didn't really need the pre-loaded SD card, but I thought it would 'smooth the way'.
>
> The only problem I've had concerned the keyboard (one is warned about this!) I didn't have a spare USB keyboard so I had to resort to one with a miniature DIN plug and the adapter as listed.
>
> I'm mightily impressed by the whole thing!
>
> Chris
>
>
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