Dendrogram
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RPi Power Supply

Thu May 31, 2012 10:42 pm

My RPi arrived and my first two days of woe were all caused by poorly performing so called USB power supplies. When tested (TP1 and TP2 with multi meter on DC volts) gave anything from 4.1V to 4.5V. MasterPlug dual and single USB supplies were the worst I tried. Phone chargers I had for LG Vewtry Snap (700mA) also not enough to hold a 5V under load. Most of these small supplies purported to be 5V at between 700mA and 2A, but none could maintain it. I have now found a 1.5A regulated supply from a broadband unit which I added a 2.5mm socket to. A Micro USB end was soldered to a 2.5mm plug, observing voltage polarity. The unit gives 5.2V with no load and 4.99V under the RPi with mouse and keyboard, both about 50mA drain. I am convinced that many users will also be finding this weak power failure out and wasting money on all manner of phone chargers and so called USB power supplies. Read the spec (700mA @ 5V constant) and use recommended supplies only, and do not just hope they will work at random. I gather that the RS 1000mA single wired micro USB one is OK and there may be many others, but cheap ones in Sainsbury's are there for a reason... they are next to useless. The second pitfall may be the voltage drop over the type of micro USB cable, if you use an old one from a phone. Some are thin wired for data and although will carry current, do drop the voltage slightly. I had trouble with the SD cards not booting. A class 10 16gb eventually worked when I got the power right. If your PI fails to boot at all, the card is suspect. If the PI boots a few dozen lines then re-boots every few seconds, then not enough Voltage. If your PI boots and will not accept keyboard commands at login, then the Voltage is just enough to boot but not enough to run USB peripherals. Mine is now happy, but after much frustration. The red power led was always lit, even on poor voltage, so no help there. The tell tail of success was the green disk access led, which is bright green flashing when working properly, but a weak and faint intermittent blink if low voltage supply. White flashing screen on Composite also indicates failed boot due to power supply weakness.

Hope some of these comments help avoid buying poor power supplies.

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jbeale
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Re: RPi Power Supply

Fri Jun 01, 2012 12:56 am

sorry to hear your tale of woefully inadequate power supplies! We do have a troubleshooting list item in the wiki relating to this, although maybe it should be reworked (or more widely known!)
http://elinux.org/R-Pi_Troubleshooting# ... F_Start-up

art san
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Re: RPi Power Supply

Fri Jun 01, 2012 7:58 am

Glad to see that you were able to overcome the difficulties, and thanks for the reminder,
inexpensive parts/accessories are just not worth the headache.
In seeking the bargain price, we sometimes do ourselves a dis-service.

Art.

Dendrogram
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Re: RPi Power Supply

Fri Jun 01, 2012 11:02 am

I have received a Nokia N97 UK 3-pin Mains Charger AC-10X in the post from Amazon this morning. It says on label: 5.0V at 1200mA. Measured across TP1 and TP2 on my RPi gives 4.82V, enough to make it work and boot. (below 4.75V probably not good enough). £3.49, post free, arrived next day UK 1st Class post, excellent service. One to consider.

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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 01, 2012 11:21 pm

It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.

It would have been much more sensible to fit a 2.5mm power socket. That would have given a massive range of alternatives, including in my case, a very stable bench power supply. Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
:D

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AndrewS
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Re: RPi Power Supply

Sun Jun 03, 2012 11:30 am

Larry_Adlard wrote:Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
As long as you're using a well-regulated 5V supply, you can just hook it up directly to the 5V and GND connectors on the P1 header.

RMW5
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Re: RPi Power Supply

Sun Jun 03, 2012 11:51 am

Larry_Adlard wrote:It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.

It would have been much more sensible to fit a 2.5mm power socket. That would have given a massive range of alternatives, including in my case, a very stable bench power supply. Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
:D
Agree with bthis. I am running with a switched mode power supply, fixed voltage 5V and very stable under load. It comes with a range of plugs, but no micro USB. The phone chargers are fine for phone charging but they are not stable enough for the R-Pi. I got mine to work by powering a USB hub from the SMPS and taking 5V from that to the power socket of the R-Pi, and connecting the same hub to the USB sockets on the R-Pi.

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Montala
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Re: RPi Power Supply

Sun Jun 03, 2012 12:23 pm

One word which is often included when talking about power supplies for the RasPi is "regulated", which the ultra cheap ones almost certainly aren't... and even some of the more expensive ones might not even emphasise the fact.

Surely it is important to ensure that whatever power supply you are using is a "regulated" one, which means (so far as I understand the term) is that it will maintain a constant output voltage, even under load.

This can of course easily be negated by then using a connecting cable of too small a cross section (as mentioned above) which could well drop the voltage to an unacceptable level.

Just a couple of points to bear in mind anyway!

TDx
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Re: RPi Power Supply

Sun Jun 03, 2012 3:03 pm

Yes endorse everything said about PSUs. My HTC phone psu at 1000mW seems to be fine but other bigger chunkier and smaller shinier ones gave spontaneously varying voltages. Although my Raspi is working fine I have noticed that switching on (i.e. plugging in the power cord) does not always work if the powered usb hub is connected. For me this is reproducible bug. Removing the hub connector and re-applying the Raspi power cord then quickly reconnecting the hub always works OK. May try making up a 4xNi-Mh cell, trickle charged by the phone charger to see how that works.
Also watch out for capacitor C6, the large one near the power connector. Mine just peeled off :( , didn't break off. Looked like a dry joints to me. Soldered back using silver solder and an Antex micro tipped iron :P . If it happens to you note which way round it goes back, the spacer has its image on the board.
Regards
Tony

smknjoe
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Re: RPi Power Supply

Tue Jun 05, 2012 6:21 am

HTC power supplies need to be removed from the wiki list of "good" power supplies. I have tested 4 or more different ones and they are not sufficient. With no devices plugged in they put out 4.71-4.76 v. Under load and with Ethernet and USB devices the Pi frequently becomes unstable.

forumisto
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Re: RPi Power Supply

Tue Jun 05, 2012 10:51 am

I have one with output 5.25 V
Will it work fine? Or not recommended to exceed 5V?
Thanks

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nick.mccloud
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Re: RPi Power Supply

Tue Jun 05, 2012 10:58 am

Larry_Adlard wrote:It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.
International take up of the Pi has overtaken some of the original design decisions - all phone chargers in the EU are going to micro USB in an effort to curb the walwart mountain from growing in the households across Europe - so as a long term view (rather like the HDMI), that was why it's the way it is.

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pluggy
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Re: RPi Power Supply

Thu Jun 07, 2012 8:41 am

The problem is that micro usb is almost exclusively used for charging phone batteries, and even with LiPo batteries, smoothing and regulation is at best down the list of priorities for manufacturers. The Pi doesn't have a battery to de-crapify the power before the sensitive bits. It isn't really any wonder most power supplies aren't up to the job because smooth clean power that doesn't have a battery in circuit to take off the lumps wasn't in the remit for the PSU. I suspect a decent size electrolytic on board the Pi would help no end.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

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NickT
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Re: RPi Power Supply

Thu Jun 07, 2012 7:38 pm

Larry_Adlard wrote:It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.

It would have been much more sensible to fit a 2.5mm power socket. That would have given a massive range of alternatives, including in my case, a very stable bench power supply. Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
:D
I couldn't agree more.

Pro tem, if RS or Farnell could find source for a male micro USB connector that one could wire into, that would be useful. I managed to Google and find a breakout board for micro USB in the US but nothing in the UK. The breakout board wasn't an ideal solution either (no shrouding)

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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 08, 2012 3:55 pm

NickT

I purchased a car cigar lighter charger from Maplin. CAT No A47KA - 7.99-UKL. The adapter reduces the voltage to 5v. I have an emergency battery box for starting cars and it has a cigar lighter socket on the side. That can deliver enough power for a few dozen Pi.

I've now hacked off the Micro-USB because I can power this from any suitable source. 7.99 is expensive just to get your hands on a connector but that the way it is at the moment.

Somehow I just don't think phone manufacturers all adopting Micro USB is going to reduce the number of wall worts. It's just something to keep ignorant politicians happy. Anyway, the truth is RPi needs to provide an alternative to USB even if it's only two holes you can solder wires into.

I know you can introduce power elsewhere on the board but I don't want to bypass the input protection attached to the Micro USB.

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abishur
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Re: RPi Power Supply

Fri Jun 08, 2012 4:31 pm

Larry_Adlard wrote: Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
:D
You mean like the 5V and Ground pin in the GPIO strip?
It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.
Micro-USB is also used in tablet devices, the kindle (and other e-readers), iPods... well the list goes on. It's actually a standard for low powered 5v devices and seeing as how prolific it is, it made it a perfect choice for powering the pi. Sure for some hobbyist there are solutions we'd like to see more, but for the hobbyist it a simple matter to find / create a work around.
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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 08, 2012 5:02 pm

abishur wrote:
Larry_Adlard wrote: Alternatively there could be a couple of holes so you can solder in wires to your own choice of connector.
:D
You mean like the 5V and Ground pin in the GPIO strip?
It was a mistake to fit a micro-USB connector for power. I think the logic was that most kids have a modern cell phone so they could use the charger. As far as I can tell Micro-USB is exclusively for cell phones.
Micro-USB is also used in tablet devices, the kindle (and other e-readers), iPods... well the list goes on. It's actually a standard for low powered 5v devices and seeing as how prolific it is, it made it a perfect choice for powering the pi. Sure for some hobbyist there are solutions we'd like to see more, but for the hobbyist it a simple matter to find / create a work around.
I also wrote:-
I know you can introduce power elsewhere on the board but I don't want to bypass the input protection attached to the Micro USB.
I'd like two holes directly connected to the Micro-USB inputs.

As someone else pointed out ALL the devices that use a cheap and nasty 5v power supply have a battery to buffer it's shortcomings. The RPi doesn't!

It's a fundamental mistake to use a charger as a power supply. They are not the same animal and they have different purposes and design parameters.

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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 08, 2012 5:09 pm

PS. A person who can afford to buy an iPad etc, doesn't need access to a cheap computer.

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abishur
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Re: RPi Power Supply

Fri Jun 08, 2012 5:25 pm

Larry_Adlard wrote: I'd like two holes directly connected to the Micro-USB inputs.

As someone else pointed out ALL the devices that use a cheap and nasty 5v power supply have a battery to buffer it's shortcomings. The RPi doesn't!

It's a fundamental mistake to use a charger as a power supply. They are not the same animal and they have different purposes and design parameters.
If you're okay with soldering all ready just unsolder the micro usb power input and attach there. True it's not through hole, but again, those who actually care that it's usb instead of something else (hobbyists) should also have the skill to modify it to fit their needs.

We've been up and down the charger vs psu debate in the past on the forums so I don't really want to get back into them, suffice to say that I do agree that its very easy to buy a crappy PSU (charger) that will crap out on you, but I also believe with a little bit of common sense when purchasing your psu, it's possible to buy/use an inexpensive yet well made PSU (charger) that will work without issue for a long long time. ;-)
PS. A person who can afford to buy an iPad etc, doesn't need access to a cheap computer.
Actually this is very untrue. Growing up my family was by no means wealthy, but we could afford a standard PC. Despite this, i wasn't allowed to come anywhere near it since it was the "family" PC and my parents needed it to do book keeping. Anytime I was allowed to use it, it booted into a menu that let me play a handful of games. Whenever a PC repair guy came over I wasn't allowed in the room because my dad was convinced PCs were a dead end and didn't want me becoming interested in them (something he held throughout my pursuit of several computer certifications and has only recently changed his mind about). So while a cheap PC wouldn't have helped me out as my dad would have been against it, it would help out those kids whose parents don't let them near the PC least they break it. Just because someone can afford to buy an iPad doesn't mean they have an excess of money to throw around. I might also make a side note that iPad/android != legitimate PC device which is sufficient for learning programming or computing any more than any gaming console would be.
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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 08, 2012 6:12 pm

Well that's exactly the point. Kids don't solder and don't understand power supplies. It's stated educational aim is to provide a platform for Python programming.

It can't fulfil that purpose without a stable power supply. Using a charger is a lottery and if it doesn't work the kids are going to be frustrated and don't have the skills to sort it out.

It's easy for me, mechanical engineer, electrical engineer, software engineer, robotics and AI. I can hack anything that's worth the effort. I'd like to program Python on this machine as a matter of principle but I have at least 4 PC's that I can use.

We're in this development phase to ensure that the kids can just plug it together and start programming and for that they need a power supply that works. A 5v regulator and a couple of capacitors is all you need but Micro USB connectors are hard to come by because the female end of the deal is a small surface mount device so the 'set' isn't something you can buy at Radio Shack or in single quantities. That's why it's a mistake.

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abishur
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Re: RPi Power Supply

Fri Jun 08, 2012 6:55 pm

Larry_Adlard wrote: We're in this development phase to ensure that the kids can just plug it together and start programming and for that they need a power supply that works. A 5v regulator and a couple of capacitors is all you need but Micro USB connectors are hard to come by because the female end of the deal is a small surface mount device so the 'set' isn't something you can buy at Radio Shack or in single quantities. That's why it's a mistake.
Sorry you lost me at this point. We're talking about kids being able to pick it up and go, which I certainly agree with, we've established that if you crappy then it's going to crap out, but we've also established that non-crappy micro usb chargers are extremely prolific, and yes, you've pointed out that most devices that use it, also have a battery backup to smooth things out, but while that theory is sound, we also have proof that using OEM chargers work with no adverse affects. And we're talking about a form factor which is the accepted industry standard and therefore extremely easy to find... but you're arguing that they're hard to come by? I think I missed something, would you mind rephrasing that?
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Larry_Adlard
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Re: RPi Power Supply

Fri Jun 08, 2012 7:27 pm

Micro USB, apart from chargers, are not common. I don't have a single device that uses this interface including two Nokia phones, one purchased last year.

As British Telecom and Philips learned years ago, if you are going to produce a million of something it cost nothing to design a totally non-standard connector. If you want small quantites of this connector it is very expensive. That raises the bar for small volume manufacturers. E.G. There is already in mini USB why not use that? Why design another one?

Do the Math. In pounds the RPi cost 24.99. The cheapest device I could find with this connector was 7.99, a third of the cost of the computer. Just to hack off the connector.

You keep repeating that there are reliable power supplies for MicroUSB. I have seen plenty of chargers but no power supplies. You only have to read scores of posts around the forum to realise this is a problem. If you are lucky the charger may work. If not and you don't understand what is going on you will blame an erratic RPi when the real problem is an unstable power supply.

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jbeale
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Re: RPi Power Supply

Fri Jun 08, 2012 7:49 pm

Is it better if you separate the power supply and the cable? There are lots of 5V USB power supplies, and the USB port <-> microUSB cable is also widely available.

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NickT
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Re: RPi Power Supply

Fri Jun 08, 2012 8:41 pm

Larry_Adlard wrote:Micro USB, apart from chargers, are not common. I don't have a single device that uses this interface including two Nokia phones, one purchased last year.

As British Telecom and Philips learned years ago, if you are going to produce a million of something it cost nothing to design a totally non-standard connector. If you want small quantites of this connector it is very expensive. That raises the bar for small volume manufacturers. E.G. There is already in mini USB why not use that? Why design another one?

Do the Math. In pounds the RPi cost 24.99. The cheapest device I could find with this connector was 7.99, a third of the cost of the computer. Just to hack off the connector.

You keep repeating that there are reliable power supplies for MicroUSB. I have seen plenty of chargers but no power supplies. You only have to read scores of posts around the forum to realise this is a problem. If you are lucky the charger may work. If not and you don't understand what is going on you will blame an erratic RPi when the real problem is an unstable power supply.
I'm in total agreement. It's not just that reliable PSUs don't exist, if you wanted to make your own regulated supply, you would have a hard job making up the flying lead to connect to the micro USB socket. I can't find a source for all the components you would need. Farnell have some, but not all the pieces referred to on this data sheethttp://www.farnell.com/datasheets/81390.pdf. The covers for the plug insert are sourced on 4000 piece reels, so that may explain why. The datasheet shows pictures of shrouds but doesn't appear to list them anywhere.

This being the case, you have no option but to go for a charger. The one I have for a Samsung seems to work OK but I've no idea what's inside it - probably very little judging by the size and weight of it, so I just have to hope that the little electrolytic and clamping diode on the Pi are up to the job of catching any nasties. The same argument applies to the 'PSU' that came with the powered hub, nominally 5V, 2 A out and 110-240V, 0.3A in, so mainly a heater that does a sideline in low voltage supply.

I think the Pi is crying out for something like a mini-jack socket in parallel with the micro USB.

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abishur
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Re: RPi Power Supply

Fri Jun 08, 2012 9:05 pm

Larry_Adlard wrote: You keep repeating that there are reliable power supplies for MicroUSB. I have seen plenty of chargers but no power supplies. You only have to read scores of posts around the forum to realise this is a problem. If you are lucky the charger may work. If not and you don't understand what is going on you will blame an erratic RPi when the real problem is an unstable power supply.
Yes, because I'm saying that the chargers are working as reliable power supplies. I read about 97% of the posts that go up on the forums, and what I've noticed is A) people keep getting messed up by a pamphlet that stated that the max PSU you can use is a 5V 500mA :roll: and B) a lot of the issue is more a factor of using wall warts with just the usb port in conjunction with very long usb cables or high resistance usb cables resulting in voltage of only 4.7V or C) cheap chargers which don't provide the power they claim to. Very *very* few people have run into a situation with an OEM charger that provides 700mA or greater, has a good usb cable, and provides 5V that creates issues on the pi.

There are ~50K pis in the world right now and it would appear that 99% of the users have been able to use what they had on hand or find a very cheap solution (where on earth are you looking? :-P) It seems like you are a part of the statistical anomalies. That's not said to marginalize your voice or discount what you have to say, just putting it in perspective here that the whole point of using the mirco usb port rather than the 3.5mm the alpha boards had was increased usability and all data points, at this point in time at any rate, point to it doing just that.

I do think there are refinements that could be done to the board in terms of power (I'm looking at you polyfuses on the USB ports!) and I like the idea of a second power plug (or better yet, a modular jack, you could simply plug on the type of power port you wanted onto two pins and it would clip into place). It's just (obvious) that I disagree that using chargers is an issue (for the most part) and by extension that the use of a micro usb port was a mistake :-)
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