[Information] Raspberry Pi Power Supplies Explanation

nothere

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Nov 25, 2012
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[Information] The ultimate Raspberry Pi power supply thread

OK, so there is a lot of talk and about power supplies and the possibility that they can cause various problems with the Raspberry Pi's performance and reliability. I have put together a small guide with information powering the Raspberry Pi.

You will need to provide a power supply that can provide enough current to power the device plus any connected devices such as keyboards, IR recievers, WIFI dongles and USB thumb drives etc as the power required by the Pi will changes depending what you have connected, whilst also taking into account inefficiencies of the supply itself and the cable between the power supply and Raspberry Pi. Use a good quality micro USB cable. Cables are notorious for giving trouble (ask the Apple TV jailbreaking community), so be prepared to swap for another one. Some chargers and power supplies are just not upto the job. They are either unregulated or simply do not output what they say they do.

Even if the Pi demands a higher current for a split second, and the power supply cant deliver, this is enough to cause freezing, rebooting or unreliable functioning of connected USB items or ethernet connection.

Each of the two USB ports on the Pi has a polyfuse rated at 140 mA, so any connected USB devices should draw less than this amount of current. In addition the polyfuse will cause a significant voltage drop, so that USB devices get less voltage than is available on the RPI itself, sometimes up to half a volt less (maybe more if the fuse has recently been hot). For regular "low power" USB devices this doesn't cause a problem as they are designed to work with voltages as low as 4.4 Volt. This isn't the case however with some USB devices such as WiFi dongles which may need 4.75 Volt, and are also known to draw more than 150 mA when configured and active (because of the problems these polyfuses caused, Raspberry PI's produced after August 25, 2012 have the USB polyfuses removed). Its worth noting that the microUSB input port still has a polyfuse which may also have enough resistance to cause problems.

The PSU may not deliver enough power. Although the maximum power requirement is said to be 700mA, that is with no peripherals connected (USB, Ethernet etc), so a 1000mA PSU should be regarded as a minimum. This allows some leeway in case the power supply cannot deliver its full power without the voltage dropping.
The cable connecting the PSU to the Pi may not be good. People have reported cables with 4 ohms resistance on the power connections. At 500mA drain this would reduce a 5V supply to 3V.
If the PSU is unregulated it can also output too high a voltage as well as too little, which may trigger the overvoltage device in the PI, which will temporarily short the 5V to ground, this will then "blow" polyfuse F3, which will take several days to recover from. Meanwhile (possibly with another PSU) the PI might not get enough power because the (partly) blown polyfuse is consuming some of the power.

There are many other things which affect the amount of power/current the Pi needs. Running a GUI will take more power. The USB devices and Ethernet connection will take power. Running the GPU will take extra power. Tinkering with over clock settings will take more power.

Please feel free to share what power supplies / power setup you have as long as you're sure its completely stable so other people can see what works. On the flip side post what didn't work eg. USB ports on TV or phone chargers.
 
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nothere

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Samsung Galaxy S2 standard charger - Locks up on accessing WIFI with USB Thumbdrive connected

LG LED TV USB port - Pi boots, but locks up when XBMC GUI starts

Cheap non branded 5v 1.0A Power supply from ebay - Locks up XBMC/reboots on any overclocking from default
 

Baz1205

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5V 2A ModMyPi HQ Raspberry Pi USB Power Supply and don't get any lock ups at all. I use them on all my PI's now. on my main PI I have an IR receiver and 4 port hub which in turn has an external drive and a keyboard connector attached.
 
May 6, 2012
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Thanks for sharing that Baz, have you tried turbo OC with raspbmc? Looks as though it should work just fine but would be nice to know whether or not it does work with that one.

I'm using the Nokia AC-10X charger and the only time I've had a lockup with these is when I try to use the "turbo" OC mode in rasbmc. In "fast" mode I can attach a wifi dongle, wireless keyboard and boot from USB with no problems so far. For the keyboard and wifi dongle I've just used a cheap 4-port USB hub from the poundshop (one without an external power source) and I was very surprised to see that work!
 

Baz1205

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Thanks for sharing that Baz, have you tried turbo OC with raspbmc? Looks as though it should work just fine but would be nice to know whether or not it does work with that one.
Indeed I have and I managed to get one of my test PI's running at 950MHz on a USB stick when the SD card dumped out on me. Just need some more time to set it up again and give it another go. Until the SD card went belly up it ran flawlessly and I was surprised how cool it was. For a few pence more I use these on all PI's I make.
 

ute

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Used the 1.5 amp Blackberry playbook charger worked great untill i added my 3.0 usb thumb, then went into reboot when loaded

Switched to the 2.1 amp Apple ipad charger with belkin cable , flawless works perfectly.
 
May 6, 2012
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As I've never had an ipad could someone post a link of what the charger looks like? I've found some generic white USB plugs which say they charge the ipad but I've never been convinced they'd be up to the job with the r-pi and finding anything official from Apple will require me to re-mortgage the house!
 

nothere

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As I've never had an ipad could someone post a link of what the charger looks like? I've found some generic white USB plugs which say they charge the ipad but I've never been convinced they'd be up to the job with the r-pi and finding anything official from Apple will require me to re-mortgage the house!
Mine looks like this.....
 
May 6, 2012
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Thanks, that looks like the generic white ones I was on about! I might have to splash out and try one then, I'll update the post once I've sourced a cheapish one and tested it.
 

nothere

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Just beware that the iPhone 4 and iPad2 chargers look the same (I have both) The Iphone is 1.0A and the iPad 2.1A, but look identical.
 

Funk

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Jan 28, 2013
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I use a iphone plug (1.0A) with a LG cable, found lying around the house. It works fine but my only peripheral is a wifi dongle. I've had a few keyboard glitches using Raspbian but nothing major...

it was only supposed to be temporary but it has worked well so far I haven't replaced yet.
 

Thug

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Apr 24, 2013
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I've had quite a number of freezes whether I've overclocked or not.

Using a 5v2A charger from ModmyPi which plugs into a 4port USB Hub. USB/Mini USB into the Pi with a USB Wi-Fi dongle and USB Keyboard/Mouse wireless dongle. To get enough power to the Pi, I've had to run an additional USB/USB cable from one of the ports on the hub into the Pi.

Will probably have to remove the wireless dongles and replace with wired cables to get a stable supply. As a matter of interest, I've put a tester on TP1/TP2 and without any load I get 5.2v
 

lowridin_guy

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May 10, 2012
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MarkRich

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May 13, 2012
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Wow thanks for that link! Do you use these with any peripherals plugged in? (wifi, remote/wireless mouse).

EDIT: after looking at shipping costs it works out to be the same price as the ones I have been ordering though.....I'm also not in the USA so my shipping charge would likely be even more.
WiFi and Remote IR Sensor. I don't use a keyboard/mouse with mine. I have zero issues with it with the two USB plugged in