linuxdesire
Posts: 1
Joined: Fri Jun 29, 2012 2:10 pm

How strict is the power supply data

Fri Jul 13, 2012 7:39 pm

Ok, I am really confused on what to use for a power supply because I do not want to burn up my Raspberry PI. I am in the United States. Could I use my cellphone charger? I read somewhere that you can use 4 AA batteries. How would you hook that up to a micro usb?

I think I am just going to order a PSU from Element 14 but would like to run my PI until then. I read that you have to have 5V and 700MA. Can you have 5V and 500MA? There is a computer store here that sells a power supply with the 5V 500MA. What is my min and what is my max.? Thank you.

User avatar
alexeames
Forum Moderator
Forum Moderator
Posts: 2869
Joined: Sat Mar 03, 2012 11:57 am
Location: UK
Contact: Website

Re: How strict is the power supply data

Fri Jul 13, 2012 8:04 pm

linuxdesire wrote:Ok, I am really confused on what to use for a power supply because I do not want to burn up my Raspberry PI. I am in the United States. Could I use my cellphone charger? I read somewhere that you can use 4 AA batteries. How would you hook that up to a micro usb?

I think I am just going to order a PSU from Element 14 but would like to run my PI until then. I read that you have to have 5V and 700MA. Can you have 5V and 500MA? There is a computer store here that sells a power supply with the 5V 500MA. What is my min and what is my max.? Thank you.
The Voltage needs to be 5.0 +/- 0.25 Volts. The Amps needs to be at least 0.7A or 700mA. It can be rated more than 0.7A, the device will take as much current as it needs as long as the voltage is correct.

So, min voltage 4.75V max voltage 5.25V
min Amps 0.7 (700mA) Max Amps - irrelevant really, but I wouldn't go for anything much over 2 Amps unless you already own it - you'll be paying too much for it.
(By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
Alex Eames RasPi.TV, RasP.iO

W. H. Heydt
Posts: 11019
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: How strict is the power supply data

Fri Jul 13, 2012 9:07 pm

alexeames wrote: (By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
So..if they all ran headless, so each Pi *would* run on 500mA, a 500MA power supply could run 10**6 Pis...sounds like a Raspberry Pi Supercomputer....

User avatar
Jim Manley
Posts: 1600
Joined: Thu Feb 23, 2012 8:41 pm
Location: SillyCon Valley, California, and Powell, Wyoming, USA, plus The Universe
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 4:54 am

I don't know how many times we need to repeat this, but, the 700 mA coming out of typical cell phone microUSB chargers is NOT, I repeat, NOT enough to power the Pi and some keyboards and mice under full CPU and GPU load. You really want an absolute minimum of 1.0 amp (1,000 mA), and 2.0 amps is much, much better (most tablet microUSB power supplies put out around 2.0 amps). These currents should be supplied with the voltage as close to 5.0 ~ 5.25 volts as possible (i.e., under load) - if the voltage is dropping down to around 4.75 volts, you could have trouble with the worst-case Pi operating loads, especially with a charger of marginal quality. These numbers also assume you're using an adequate-gauged (wire thickness) USB-to-microUSB cable typically supplied with these chargers/supplies.

When it comes to reserve current capacity, more is better, and much more is much better. You do NOT want to be running your Pi with a borderline supply and then, one day, when you do want to show off some software that maxes out the graphics and processing capabilities of the Pi, it goes dark and cold. It's no fun ... at all.

Do not tempt Murphy, for he will laugh in your face at your foolishness.
The best things in life aren't things ... but, a Pi comes pretty darned close! :D
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!

Dilligaf
Posts: 283
Joined: Wed May 23, 2012 6:48 pm

Re: How strict is the power supply data

Sat Jul 14, 2012 5:23 am

alexeames wrote:[quote="linuxdesire"
(By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
By the way A means amps :lol: :lol:

W. H. Heydt
Posts: 11019
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: How strict is the power supply data

Sat Jul 14, 2012 6:18 am

Dilligaf wrote:
alexeames wrote:[quote="linuxdesire"
(By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
By the way A means amps :lol: :lol:
If you're going to be that way about it...A means Amperes.

User avatar
alexeames
Forum Moderator
Forum Moderator
Posts: 2869
Joined: Sat Mar 03, 2012 11:57 am
Location: UK
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 7:35 am

Dilligaf wrote:
alexeames wrote:[quote="linuxdesire"
(By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
By the way A means amps :lol: :lol:
:lol: when you multiply Volts by Amps you get Watts. Hence the 2,500.
Alex Eames RasPi.TV, RasP.iO

User avatar
alexeames
Forum Moderator
Forum Moderator
Posts: 2869
Joined: Sat Mar 03, 2012 11:57 am
Location: UK
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 7:43 am

Jim Manley wrote:I don't know how many times we need to repeat this, but, the 700 mA coming out of typical cell phone microUSB chargers is NOT, I repeat, NOT enough to power the Pi and some keyboards and mice under full CPU and GPU load. You really want an absolute minimum of 1.0 amp (1,000 mA), and 2.0 amps is much, much better (most tablet microUSB power supplies put out around 2.0 amps). These currents should be supplied with the voltage as close to 5.0 ~ 5.25 volts as possible (i.e., under load) - if the voltage is dropping down to around 4.75 volts, you could have trouble with the worst-case Pi operating loads, especially with a charger of marginal quality. These numbers also assume you're using an adequate-gauged (wire thickness) USB-to-microUSB cable typically supplied with these chargers/supplies.

When it comes to reserve current capacity, more is better, and much more is much better. You do NOT want to be running your Pi with a borderline supply and then, one day, when you do want to show off some software that maxes out the graphics and processing capabilities of the Pi, it goes dark and cold. It's no fun ... at all.

Do not tempt Murphy, for he will laugh in your face at your foolishness.
Jim. I agree with you that more capacity is better than less. But 700 mA is enough - UNLESS you are using high power peripherals and no powered hub. Having said that, I'm routinely using one of the cheap Nokia 1 Amp chargers and it works a treat (only about £3 too). My Samsung 700 mA charger works equally well, but I use that for my phone. :lol:

I don't disagree with you, but I think you're overstating the case. ;)
Alex Eames RasPi.TV, RasP.iO

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4258
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 8:20 am

W. H. Heydt wrote:
Dilligaf wrote:
alexeames wrote:[quote="linuxdesire"
(By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
By the way A means amps :lol: :lol:
If you're going to be that way about it...A means Amperes.
No. A means amperes.

When the unit is someone's name, then it is not capitalised. (But the abbreviation is, hence A)

2 Amperes looks like this:

ImageImage

See also V: volts and W: watts.

:P

User avatar
teh_orph
Posts: 346
Joined: Mon Jan 30, 2012 2:09 pm
Location: London
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 10:04 am

rurwin wrote:2 Amperes looks like this:

ImageImage

See also V: volts and W: watts.

:P
First proper chuckle of the day!
I'd be interested to know your thoughts on 700mA...I can think of at least two ways to do this.

Back on topic: I've had the most luck with my PC's USB port for power and a very short lead. Using my SGS2 charger I get good values with TP1 and TP2 but my USB devices sometimes give weird results - so there may be more to it than simply 5v +/- 0.25, 700mA.

User avatar
Jim Manley
Posts: 1600
Joined: Thu Feb 23, 2012 8:41 pm
Location: SillyCon Valley, California, and Powell, Wyoming, USA, plus The Universe
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 2:30 pm

alexeames wrote:I don't disagree with you, but I think you're overstating the case. ;)
Alex - those of us familiar with the details all understand the various issues. The problem is that the Pi is aimed at people on a budget and they're going to be tempted to use the cheapest, most marginally-made peripherals that happen to by lying around, that often aren't very efficient and may not meet the specs stamped on them, especially when the load is at maximum for an extended period of time. They're going to have a bad experience and not understand what's causing the problem, and then they'll be wasting the bandwidth and brainwidth of people trying to support them. The wave of 100,000 boards is just now washing up on the beaches, and we're going to start seeing yet-another tsunami of the same old questions and requests for help from people who have probably never looked at the FAQs, Getting Started pages, etc., much less the advice in these forums.

When it comes to fending off the mobs carrying torches and pitchforks, you can't overstate the case enough - just ask Dr. Frankenstein! :shock:
The best things in life aren't things ... but, a Pi comes pretty darned close! :D
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!

User avatar
alexeames
Forum Moderator
Forum Moderator
Posts: 2869
Joined: Sat Mar 03, 2012 11:57 am
Location: UK
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 3:37 pm

Jim Manley wrote:When it comes to fending off the mobs carrying torches and pitchforks, you can't overstate the case enough - just ask Dr. Frankenstein! :shock:
Lol maybe that guy with the MegaAmps was right? :D
I guess, the chances are that even a crappy 2A supply will be able to maintain voltage pulling 1A. Very pleased with my 1A Nokia charger for £3 though. I don't think people can go wrong with those (unless they try to power an external HDD with it - and someone will :lol: )
Alex Eames RasPi.TV, RasP.iO

User avatar
Lob0426
Posts: 2198
Joined: Fri Aug 05, 2011 4:30 pm
Location: Susanville CA.
Contact: Website

Re: How strict is the power supply data

Sat Jul 14, 2012 5:42 pm

I have been using an iPhone charger (1A). It works just fine with a 1 foot USB cable. It worked ok with a 3 foot cable but the keyboard stuttered a bit. It would power, reboot, power with a 6 foot cord. By the time you lose voltage through the USB cable, then a little again at F3, then again at F1 or F2, you just do not have enough voltage to get it done with the keyboard or mouse. The smaller polyfuses are just too high of resistance. My charger starts out at 5.08v It drops to 5.02v at TP1/TP2. Just the loss from the 1 foot cable and F3. I have not tested the ohms of F1/F2 yet but most people are claiming they can be pretty high, as much as 7 ohms.

On the Lapdock I am getting 5.03v at TP1/TP2.
With the short cable or the Lapdock I have no USB problems at all. Some people are having problems with just about any charger. My theory is that they ended up with a RasPi that has polyfuses that are all at the high end of the ohms rating. Or cold solder joints as has been found.
512MB version 2.0 as WordPress Server
Motorola Lapdock with Pi2B
Modded Rev 1.0 with pin headers at USB

http://rich1.dyndns.tv/
(RS)Allied ships old stock to reward its Customers for long wait!

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 12357
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: How strict is the power supply data

Sat Jul 14, 2012 5:57 pm

Yes, unlike proper power supplies, chargers are often not properly regulated, so they drop voltage a lot when loaded. Unloaded the could output six volt, but when loaded with the PI running a GPU intensive program (consuming more power) they could drop to 4 Volt.
That is the reason some PI's work well in the shell, but start having trouble when running the GUI.
The higher rated models would normally drop a little less than lower rated models.
real regulated power supplies would keep the output at almost exactly 5 volt, no matter the current drain.

donde
Posts: 79
Joined: Sat Feb 18, 2012 3:57 am

Re: How strict is the power supply data

Sat Jul 14, 2012 7:29 pm

I'm routinely using one of the cheap Nokia 1 Amp chargers
I use a Garmin GPS charger, putting out 5 volts, and capable of 1 amp current draw. It's a switching supply and very small. Works great...no heat

Bakul Shah
Posts: 321
Joined: Sun Sep 25, 2011 1:25 am

Re: How strict is the power supply data

Sat Jul 14, 2012 7:51 pm

W. H. Heydt wrote:
alexeames wrote: (By the way M means Mega, m means milli. So 5V 500 MA would be 2,500 MegaWatts :o )
So..if they all ran headless, so each Pi *would* run on 500mA, a 500MA power supply could run 10**6 Pis...sounds like a Raspberry Pi Supercomputer....
A billion Pis, not million! For your superpi computer you will also need a 2.5 Giga Watts power generator and a very large heat sink. Doable. With a grain of salt.

User avatar
Grumpy Mike
Posts: 914
Joined: Sat Sep 10, 2011 7:49 pm
Location: Manchester (England England)
Contact: Website

Re: How strict is the power supply data

Sun Jul 15, 2012 7:23 pm

Power in a picture:-
Image

User avatar
RichardUK
Posts: 235
Joined: Fri Jun 01, 2012 5:12 pm

Re: How strict is the power supply data

Sun Jul 15, 2012 9:06 pm

my quick answer, I use the charger for my Samsung Galaxy S2. So order one of these. I have also used my PC and a normal phone USB data cable.

pygmy_giant
Posts: 1562
Joined: Sun Mar 04, 2012 12:49 am

Re: How strict is the power supply data

Sun Jul 15, 2012 9:32 pm

This thread: http://shkspr.mobi/blog/index.php/2012/ ... i-success/ indicates that there are also limits to the periferals that can be powered through the USB without a powered hub - annoying isn't it.

Nikola Tesla looks like this:

Image
Ostendo ignarus addo scientia.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4258
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: How strict is the power supply data

Sun Jul 15, 2012 10:28 pm

Image

It seems that any HTC charger is good.

Some people say the iPhone chargers work, some that they don't. It seems to me that it is in all likelihood a problem with the cable, since of course, the Apple chargers do not come with one.

The AA battery thing is a bug in the FAQ and hence in Farnell's documentation. The Raspberry Pi cannot be powered directly by battery, and if it could, the batteries would not last long. The information that it can relates to the alpha prototype and is now invalid.

User avatar
Lob0426
Posts: 2198
Joined: Fri Aug 05, 2011 4:30 pm
Location: Susanville CA.
Contact: Website

Re: How strict is the power supply data

Mon Jul 16, 2012 2:52 am

The Apple chargers do work just fine, if you use a short cable, or a good brand cable. They put out between 5.03v and 5.08v for the ones we have tested. The cheap cables like some at Wal-Mart would work if your charger puts out near 5.2v. The Apple chargers stay steady even under a heavy load, near max output.
512MB version 2.0 as WordPress Server
Motorola Lapdock with Pi2B
Modded Rev 1.0 with pin headers at USB

http://rich1.dyndns.tv/
(RS)Allied ships old stock to reward its Customers for long wait!

User avatar
edent
Posts: 25
Joined: Thu Sep 08, 2011 3:41 pm
Contact: Website

Re: How strict is the power supply data

Tue Jul 17, 2012 4:40 pm

One thing to say - take a look at the label printed on the charger. It should tell you what Voltage & Amperage it will pump out.

For example, I'm using a BlackBerry PlayBook charger - it's 5.0V @ 1.8A. Perfect :-)

User avatar
alexeames
Forum Moderator
Forum Moderator
Posts: 2869
Joined: Sat Mar 03, 2012 11:57 am
Location: UK
Contact: Website

Re: How strict is the power supply data

Tue Jul 17, 2012 6:05 pm

edent wrote:One thing to say - take a look at the label printed on the charger. It should tell you what Voltage & Amperage it will pump out.

For example, I'm using a BlackBerry PlayBook charger - it's 5.0V @ 1.8A. Perfect :-)
If it's a real copy (ie not a knock-off) of a "proper" brand like HTC, Samsung, Apple, Nokia etc the figures will probably be accurate. If it's a cheap no name power supply off ebay, the figures could be wildly out (and if the voltage is too high - that could be disastrous.)
Alex Eames RasPi.TV, RasP.iO

User avatar
AndrewS
Posts: 3625
Joined: Sun Apr 22, 2012 4:50 pm
Location: Cambridge, UK
Contact: Website

Re: How strict is the power supply data

Tue Jul 17, 2012 6:53 pm

Bakul Shah wrote:A billion Pis, not million! For your superpi computer you will also need a 2.5 Giga Watts power generator and a very large heat sink. Doable. With a grain of salt.
www.youtube.com/watch?v=mjCRUvX2D0E :D

Return to “General discussion”