Some people seem to have had problems with their power supplies. By contrast I bought two which work perfectly from Amazon in the UK for £3.69 each including postage.
I cannot provide a URL to the specific PSU that will exist long-term but the ad was marked as "EXTRA LONG UK Micro USB Mains Power Wall Supply Charger For Raspberry Pi". Rated at 1000mA or 1A. Seems fine.
With a similar motivation to the thread about cases (q.v.) would anyone else like to recommend a PSU for the Raspberry Pi?
Even better, for those with applications where more USB ports are needed why not have a mains-powered USB hub which includes space and power for the Pi? The Pi could plug in to it. Then one mains lead would power both.
I did the 7805 thing for a while when I was having real trouble getting the Pi to run with the wall-warts I had. My standard 5V bench widget worked fine for that. It's a 7805 bolted to the inside of a little Hammond aluminum box on the 1"x2"x3" scale. It was feeding P1 at pins 2 and 6. It ran for long periods, got very warm, but never cut out. I've built a new model widget lately around some adjustable switching regulators that you can get for 2 or 3 bucks. Runs much cooler, of course. I'm finding that the micro-USB connector is the most difficult thing about powering the Pi.
If you don't want the heat these things are intended to spent a lot of volts down to 5v to drive RC gear
You might even be able to use the variabale pulse width 'shut the throttle, the battery's flat' pin as well :-)
(in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
I just made a *real cheap* switch by getting a Maplins SPST rocker switch, and a small plastic box to put it in. I ran the USB cable through the box and carefully cut and removed the outer case to expose the four wire bundle inside. I cut through the *red* wire, stripped 3mm of insulation off both the cut ends and soldered them onto the tags on the switch.
Works perfectly and the micro-USB is now permanently plugged into the RPi.
martin@ | Martin Gregorie
gregorie. | Essex, UK
Following up: ============= The numbers below were read off a Maplins mains wattmeter plugged between the mains socket and the Farnell-supplied USB adapter.
My Mains:USB adapter draws 0.0 W with the RPI off. While the RPi is booting it draws up to 2.8 W before settling to a steady 2.4W with the RPi idle.
I have a fully patched (as of last Friday) Debian Wheezy 512MB RPi B that I bought just after the 512 MB version was released. It is running headless with nothing connected except the Ethernet cable and the USB power cable.
Given this USB adapter's standby consumption I'm not at all bothered by the cost of leaving it plugged in 24:7. As a reality check it is no warmer than nearby chunks of plastic such as other vanilla 13A plugs and socket surrounds.
martin@ | Martin Gregorie
gregorie. | Essex, UK
On Tue, 7 May 2013 00:33:09 +0000 (UTC), Martin Gregorie wrote in :
I bought some three-way mains adapters at Aldi with individual switches (and LED indicators) built in. Works great for switching off monitors, powered speakers, etc. when leaving the Rechenzentrum for any length of time. Also helps distribute power to tablets and laptops from one Swiss-to-UK adapter when I'm staying at CERN.
Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
A somewhat related question: what about using a USB hub for powering a few Pis, I'm thinking 2 to 4 units? Somebody quoted figures around a little less than 3W power consumption for a single Pi, so a single good-quality powered hub should give more than enough power; has anybody tried this?
You'll have to be careful with your choice of hub - some will only supply 500mA per port, you need one that can manage 1000mA per port (which I believe is the maximum that the RPi can draw, although without any USB devices attached it will be less - aiming for maximum capacity should ensure stable well regulated supply).
I have a cheap chinese 7 port powered hub with a 5V 3A PSU that runs a pi and several power hungry peripherals (USB attached discs, charging phones etc.) without any trouble at all. The only issue I have with it and the pi is that it partly powers the pi through the USB port that controls it as well as through the power connector plugged into it. I don't see why it wouldn't power several Pis.
Steve O'Hara-Smith | Directable Mirror Arrays
C:>WIN | A better way to focus the sun
Raspberry Pi power is so critical for the Pi, that I expended a whole chapter on it in my new book "Assimilating the Raspberry Pi".
If you use the LM7805 for example (as mentioned up thread), to regulate some higher voltage down to 5V, you have two limitations:
1) you need an input voltage at 2 volts minimum higher (7V) than the output (5V)
2) you have a limited power dissipation capability for the regulator (10.5W)
The difference between input and output voltages is dissipated as wasted energy, hence the need for a good heat sink. If you assume the minimum current of 0.7A with a 2 volt drop, that is 1.4 Watts of energy wasted (this increases as input voltage or current draw increases). Wasted energy is bad for battery operation, obviously.
Also, an LM7805 rated at a max of 1.5A (@5+2=7 volts), is then limited to handling 10.5 watts of power. If you increase the input voltage, then the maximum output current drops below 1.5A (otherwise it the device thermally shuts down). The book illustrates these calculations.
Thermal shutdown is not a win either-- it does so by dropping the output voltage below 5V (brown outs). Clearly not an operationally good thing.
The best cheap solution is either a wallwart that regulates well at 2A or better, or to use a DC-DC buck converter PCB, between a higher input voltage power source (battery/power supply) and the Pi. In an experiment I documented in the book, I used a cheap ebay buck converter which provided about 72% efficiency. In that particular experiment, the input was about 15V from a surplus switching power supply that I had removed from a piece of equipment.
Checking the various forums, you'll note that many people experience problems when the GPU is active (using HDMI output), or their networking stops working. The 700mA should be viewed as a minimum, which is before the GPU becomes active. With the GPU busy, you'll reach peaks nearing 1A or so. Most 1-1.5A wallwarts won't keep up with the changing GPU demands fast enough. I would consider 2 Amps as a minimum unless you plan on ssh-ing into the Pi without HDMI support.
As an aside, I have used my ebook reader's power supply rated at 2A successfully, with the Pi. So if you have one of those kicking around in the house, that may be another option.