Raspberry PI Power

[William Weaver]

Colin,

My bet is that the logitech unifying receiver and the wifi are both
requesting a high current usb connection, which is then saturating your 1A
power source when the RPis load gets high. Would it be possible for you to
measure your current draw from the externally powered power supply?

Also something I've been doing, I have a monitor with USB built into it, I
plug my power cable from the pi into the monitor powered USB hub, then the
ubhub into the pi. The pi gets power from the usb hub (which doesn't have a
data line so it doesn't create a loop issue, and the other ports are
available for usage. Best of all my monitor's power switch becomes a hard
power switch for the pi.

In your case you may be able to take the usb hub and with a bit of
soldering put it on one of the rails of the lcds power supply. I'd
definately check spec sheets and do some testing before you broke out the
iron though.

Will


On Fri, Aug 2, 2013 at 12:14 PM, Colin McGregor <colin.mc151-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>wrote:

> On Fri, Aug 2, 2013 at 12:02 PM, Scott Sullivan <scott-lxSQFCZeNF4 at public.gmane.org> wrote:
> > 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?
>
> Revision 2, with 512 MB of RAM, made in the UK, so board revision
> doesn't seem to be the issue.
>
> Thanks for the thought though.
>
> > 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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