Raspberry PI Power

[Scott Sullivan]

On 08/02/2013 11:09 AM, Colin McGregor wrote:
> Sorry about a subject line that sounds like a tacky children's
> cartoon, but it is an issue I am looking at.
>
> I wanted to set-up a Raspberry PI with a 19" LCD screen at my kitchen
> table. Connected to the Raspberry PI I had an Ourlink WiFi dongle and
> a Logitech Unifying receiver to support a wireless keyboard/mouse (*).
> Initial set-up with several different "1 amp" output transformers had
> the same result, the Raspberry PI ran, but the WiFi connection was
> unusable. Powering the Raspberry PI off a 4 port USB hub that has a
> 2.6 amp power supply and moving the WiFi dongle to the hub has
> resulted in a very solid set-up. So, power seems to be the issue, but
> where is the question. Am I looking at :
>
> - a Raspberry PI with noted accessories using more than 1 amp of power?
> - transformers that claim to be "1 amp" not putting out 1 amp to the
> Raspberry PI?
> - a Raspberry PI getting enough power, but not being able to pass
> enough to the accessories?
> - another issue I have not thought of?

Colin,

I assume you have a model B (as you have two USB ports). But which revision?

The revision 1 boards had poly fuses that clamped the output of the USB 
ports to 100mA each. The USB spec only guarantees 100mA and the device 
is supposed to request more in 100mA increments up to 500mA. In practice 
this is largely ignored and the whole 500mA is usually provided. The 
Foundation was trying to be protective in the face of many 500-750mA 
chargers on the market at the time. But it cause more head scratching 
then problem solving.

http://elinux.org/images/archive/9/96/20120908163029!RpiFront.jpg

The revision 2 boards did away with them at community behest.

http://elinux.org/images/9/96/RpiFront.jpg

I had the same experience with my revision 1 board. You actually can 
by-pass the poly fuses (the two large green component in the top right 
corner of the board). You just need to solder a wire in place.

Example:
http://imgur.com/a/mIhaR
-- 
Scott Sullivan
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