Looking after your Pi – Part 1 – The Importance of a Quality Power Supply (PSU)

When I took delivery of my original Raspberry Pi (Model B) the board arrived packed in a sturdy plastic case, not unlike an audio or DAT cassette box (a reference which instantly shows my age…)

In contrast, the Pi 2 arrived in a flimsy cardboard box, with absolutely no crumple protection.

image

My first Pi 2 actually had to be returned as there was damage to the relatively fragile board. This raised questions in my mind regarding the robustness of the unit, and best practices for general usage and handling.

Some of the topics I’ll be covering in this and the next post are:

  • Hardware damage vs ‘soft’ damage (configuration errors and data corruption)
  • Power supply and usb cable quality
  • Power supply voltage, amperage, and order of connection to the Pi
  • The importance of a 2amp Psu when attaching peripherals via Usb
  • Usb cable quality technicalities: 2828 AWG vs 2824 AWG grades
  • General handling of the Pi, electrostatic discharge, and using an enclosure
  • Best pratices for connection and disconnection of peripherals
  • Pi shutdown and SD card handling

It is important to note that the Raspberry Pi was designed from the outset to be a system for learning about all aspects of computing; as such it doesn’t come housed in a bullet-proof case, it doesn’t come with a power supply that is guaranteed to work, nor does it come with a compatible SD card (which acts as the system’s hard disk, or more accurately, like a contemporary desktop or laptop’s SSD).

Like all consumer grade electronics, it is possible to physically break the Raspberry Pi, and to do so in a manner in which the damage is impossible to discern (such as by electrostatic discharge).

It is much more likely, however, that any damage the Pi suffers is in the form of corrupted configuration or data files (which can be resolved by restoring from a backup – not a problem as everybody takes regular backups of their system… don’t they?). I’ll be covering problems caused by configuration errors and data corruption in a later post

Given that physical damage is a possibility, it may be worth listing a few of the tips I came across for safe handling of the system, some advice I found specific to the power supply requirements, and also possible issues regarding MicroSD cards.

Power Supplies (Micro Usb / PSU)

Although the Raspberry Pi uses a standard micro usb connector for the main power supply (psu), the rated power output (amps and volts), and the build quality of the unit used is very important.

Whilst it is possible to boot the Pi using the Usb output from a variety of sources (such as the TV the Pi is connected to, or a laptop Usb port), once the Pi is under load various problems can arise when the Cpu, graphics processor, Usb ports etc begin to demand more and more power (which is especially evident with many of the emulators which are driving the Pi to the limits of what can be delivered).

In short, by consensus (or, more accurately, from my sampling of a number of forums, and having read a few relevant books), the Pi should be powered from a dedicated Micro Usb PSU, with an integrated cable, able to deliver 5 volts and at least 1.2 amps (preferably 2 amps).

[EDIT] Since this post was written the Raspberry Pi 3 has been released. The increased capabilities of this machine, including in-built WiFi and Bluetooth, along with a faster quad-core processor, result in increased peak power consumption. As a result, for the Pi 3 the recommended PSU specification is 5 volts and 2.5 amps.

A very useful guide covering a range of Raspberry Pi issues can be found on the RaspberryPi.org forums Common pitfalls for beginners; the following are a couple of useful entries relating to the importance of a quality psu are:

Bad power indications caused by power supply unit (psu) or cable problems – covers the Pi entering a boot-up loop; the importance of quality usb cables; power brown-outs indicated by a rainbow icon on the display, and by the power Led on the board

Warning! adapters might output more than 6V without load – related to the previous link, this covers psu over-voltage and blown polyfuses

A key comment from this entry:

“Our advice would be to first plug in the micro-USB connector, and only then plug in the wall wart, or use the power switch on the power bar to switch power on and off.”

It is worth noting that the official Raspberry Pi Regulatory Compliance and Safety Information Pdf states:

“This product shall only be connected to an external power supply rated at 5V dc, and a minimum current of 600-1800mA. Any external power supply used with the Raspberry-Pi shall comply with relevant regulations and standards applicable in the country of intended use”

Note however that the Pdf refers to “Raspberry Pi Model B+” specifically, rather than the newer Pi 2 model B, and appears to contradict both the de facto advice to use a 2 amp PSU, and the fact that the officially branded PSU available from RS Components is a 2 amp unit.

Some more specific advice can be found on the RaspberryPi.org forums, for example in a post by forum user klricks

“The maximum current into the RPi is limited to 2A. The maximum current to all of the USB ports combined is 1.2A so that leaves 0.8A for the RPi+ anything connected to the GPIO’s

You need to find the current draw specification of each USB device and add them up. If 1.2A then you will have to use a powered HUB.

Note the default USB power output is 600mA. You must change a configuration setting to get the max 1.2A

So as mentioned you can’t go wrong with a 2A supply. A smaller supply can be used for the server with no peripherals.
A larger than 2A supply can be used but has no added benefit.”

Advice is also found in the excellent Raspberry Pi User Guide (2nd edition) by Eben Upton (‘co-creator of the Raspberry Pi’), and Gareth Halfacree:

“The formal USB standard states that devices should draw no more than 500 mA, with even that level of power only available to the device following a process called negotiation. Because the Pi doesn’t negotiate for power, it’s unlikely that it will work if you connect it to the USB ports on a desktop or laptop computer.”

(chapter 4, troubleshooting)

Especially important if your Pi is powered from a mains adaptor which does not have an integrated cable is the quality of the Usb cable; for an interesting article on how this can drastically affect not only how the Pi will work, but also a range of other issues including the time required to charge a device, see: Not all micro Usb cables are equal – if you have a tablet watch out for 2828 awg vs 2824 awg

Continued in Part 2 – General Handling

Related Posts
Links: Raspberry Pi and Gaming Emulation via RetroPie

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