PedroC1999
Posts: 13
Joined: Wed Feb 04, 2015 9:24 pm

Power Requirements For A RPi2?

Thu Feb 05, 2015 8:12 am

The Pi2 has had a big improvement performance wise, what does this mean in terms of Amperage needed to power the device?

Does the Pi2 supply 500ma (if available) to all USA ports?

What would you recommend the 'charger' amperage to be rated at? 2a? 5a?

Thank you.

fruitoftheloom
Posts: 24497
Joined: Tue Mar 25, 2014 12:40 pm
Location: Delightful Dorset

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 8:48 am

PedroC1999 wrote:The Pi2 has had a big improvement performance wise, what does this mean in terms of Amperage needed to power the device?

Does the Pi2 supply 500ma (if available) to all USA ports?

What would you recommend the 'charger' amperage to be rated at? 2a? 5a?

Thank you.
The USB is exactly the same as the B+, 600ma by default in total, this can be changed to 1.2A see

https://projects.drogon.net/testing-set ... berry-pi-b

There was a recent post here which recommended that a 2A Power Brick is best for both the B+ & Pi2
Thinking outside the box is better than burying your head in the sand...

ktb
Posts: 1447
Joined: Fri Dec 26, 2014 7:53 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 9:04 am

I'm thinking I'd actually recommend something over 2A after trying the Pi2B.

User avatar
RaTTuS
Posts: 10601
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 9:08 am

TBH - I'd recommend a 3A PSU
quality one also

as if you are driving the USB fully [ok - not likely but ....]
1.2A
for that
.8A for the RPI
do you want a camera ? another .3A
and you really need a bit of headroom on the PSU
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

BMS Doug
Posts: 3915
Joined: Thu Mar 27, 2014 2:42 pm
Location: London, UK

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 9:15 am

Be wary of spending to little on your power supply, a cheap "charger" claiming to supply 5V 2A may turn out to only be capable of supplying one or the other, not both simultaneously. There is also a risk that a cheap power supply may have insufficient separation between mains and low voltage lines, leading to risk of fire or explosion (I'm not joking).

Paying a bit more for a decent power supply is worthwhile.
Doug.
Building Management Systems Engineer.

User avatar
pluggy
Posts: 3635
Joined: Thu May 31, 2012 3:52 pm
Location: Barnoldswick, Lancashire,UK
Contact: Website

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 11:01 am

You won't get more than 1.8 amps through a single Micro-USB connector however much the power supply is capable of. Since the CPU current draw of the old Pi was all but insignificant, I can't see the much more powerful Pi 2 eating that much more, the CPU will still be a minor player in the current stakes. Before having recieved my 2B, I reckon it will use no more than 500mA for the whole Pi. I'll wire it up when it arrives and find out.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

User avatar
pluggy
Posts: 3635
Joined: Thu May 31, 2012 3:52 pm
Location: Barnoldswick, Lancashire,UK
Contact: Website

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 12:54 pm

Its arrived and a quick and dirty test with my oft derided Samsung 700mA charger with a mouse, keyboard and wifi dongle runs it fine. Previous measurement show the Keyboard & Mouse use ~20mA each and The Wifi dongle ~50mA. The coloured square low voltage warning comes up for about 2 seconds when its first fired up but rapidly disappears. But since a B+ does exactly the same with the same puny charger, it says to me its not a whole lot different than the B+. I'll get something a little more technical in line when I've a bit of time.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

hippy
Posts: 8537
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 1:08 pm

RasPi.TV have done some current measurements which are quite encouraging, comparable to a B+ when running single core ...

http://raspi.tv/2015/raspberry-pi2-powe ... easurement

User avatar
pluggy
Posts: 3635
Joined: Thu May 31, 2012 3:52 pm
Location: Barnoldswick, Lancashire,UK
Contact: Website

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 2:00 pm

A long way shy of the old model B with its inefficient linear voltage regulators, which is what I was expecting. Since the original specs for the B said 700mA, I'll stick with my Samsung charger. I suppose 3A would be OK if you're spot welding something with the Pi.....

There always has been a lot of hokum spouted regarding power on here. I suspect cheap nasty 3A supplies will just about keep up with supplying a few hundred mA at the requisite voltage.

If it really did need 3A, the foundation would have put something a little more conducive to carrying that amount of power than a puny Micro-USB.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

ktb
Posts: 1447
Joined: Fri Dec 26, 2014 7:53 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 2:29 pm

I was warned that even the momentary rainbow-square on boot that fades away is a problem. I'm not sure I believe it. I seem to recall someone mentioning a spike at boot is to be expected on the Pi2B. I see it with a decent 2A Samsung charger.

User avatar
solar3000
Posts: 1059
Joined: Sat May 18, 2013 12:14 am

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 3:22 pm

pluggy wrote:You won't get more than 1.8 amps through a single Micro-USB connector however much the power supply is capable of. Since the CPU current draw of the old Pi was all but insignificant, I can't see the much more powerful Pi 2 eating that much more, the CPU will still be a minor player in the current stakes. Before having recieved my 2B, I reckon it will use no more than 500mA for the whole Pi. I'll wire it up when it arrives and find out.

How did you imagine that micro usb can only carry 1.8A?


28 guage micro USB Cable:
64.9ohm/1000ft
64.9/166.66666666666666666666666666667=0.38939999999999999999999999999999 OHM / 6ft

E=I*R
5 V / 0.38939999999999999999999999999999 OHM = 12.840267077555213148433487416539 Amps

-------
24 guage micro USB Cable:
25.67ohm/1000ft
25.67/166.66666666666666666666666666667=0.15402 OHM / 6ft

E=I*R
5 V / 0.15402 OHM = 32.463316452408778080768731333593 Amps
Antikythera

User avatar
RaTTuS
Posts: 10601
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 3:29 pm

there is some mention on teh web about the pin sizes on the microusb adapter that is only rated for 1.8Amp
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

PedroC1999
Posts: 13
Joined: Wed Feb 04, 2015 9:24 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 3:49 pm

So a 2.1 Samsung S5 Charger should do the trick?

What if I eventually add a camera (Official Pi) etc, would it still be okay?

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 27415
Joined: Sat Jul 30, 2011 7:41 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:05 pm

I believe the uUSB connector is rated for up to 5A (USB max charging current). Not sure where the 1.2 mentioned above figure comes from.

But I power a P2 off my laptop, so I doubt that's even 1.5A. Get the rainbow on startup, but can run the camera and a h264 encode/decode at the same time without a problem.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed.
I've been saying "Mucho" to my Spanish friend a lot more lately. It means a lot to him.

User avatar
blachanc
Posts: 466
Joined: Sat Jan 26, 2013 5:03 am
Location: Quebec,canada(french)

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:06 pm

Careful with calculations... You need to keep a minimum voltage @ the Pi input.

Amps vs cable type

I bought Samsung 2A charger from a well-known Chinese re-seller :lol: . They can only output .75A (as they are fake)
As long as you stick with Pi-friendly resellers, you should be fine.

Ben
PS: in my car, after few months my phone (using google maps) would discharge even when plugged using a REAL 2 AMP power supply. The phone was showing that it was in charging mode.
The culprit was the micro USB tip of the 24/28 AWG USB cable. It was corroded by the salt we put on roads during winter.
Theoretical values vs fields values can vary by a lot. ;)
Autism/Asperger syndrome: what is your score on this quiz?
http://www.raspberrypi.org/forums/viewtopic.php?f=62&t=70191

PedroC1999
Posts: 13
Joined: Wed Feb 04, 2015 9:24 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:31 pm

I have an authentic S5 2.1 A charger, so I should be fine correct?

User avatar
pluggy
Posts: 3635
Joined: Thu May 31, 2012 3:52 pm
Location: Barnoldswick, Lancashire,UK
Contact: Website

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:32 pm

Depending on which spec sheet and its age The figures vary between 1.5 A and 2 A for micro USB, it is related to the size of the tiny gold plated connectors at the point of contact rather than cable sizes.

Its a moot point anyway. My shiny new Pi 2 browsing the web with epiphany with a directly connected USB keyboard, Mouse & Wifi Adaptor is showing 5.07 volts across the 5v & Gnd Pins with a way too puny (according to many on here) 700mA Samsung Charger. The same one that shows the rainbow square briefly at power on. I'm prepared to go with RaspTVs figures, which shows the Pi2 at full whack uses less power than the original model B. Much to be said for more efficient switch mode voltage regulation on the newer models.

If you're stuck with seperate power leads, make sure they are decent quality, the power supply can be top notch but if the cables are made from damp thread......

You'll only need above 1 amp if you're using a bus powered hard drive by my reckoning. The typical 'Nano' wifi adaptor would get frightening hot very quickly if it were using much above 100 mA (0.5 watts)
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

User avatar
blachanc
Posts: 466
Joined: Sat Jan 26, 2013 5:03 am
Location: Quebec,canada(french)

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:35 pm

PedroC1999 wrote:I have an authentic S5 2.1 A charger, so I should be fine correct?
Yes,

This should be fine.

Ben
Autism/Asperger syndrome: what is your score on this quiz?
http://www.raspberrypi.org/forums/viewtopic.php?f=62&t=70191

User avatar
pluggy
Posts: 3635
Joined: Thu May 31, 2012 3:52 pm
Location: Barnoldswick, Lancashire,UK
Contact: Website

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:36 pm

PedroC1999 wrote:I have an authentic S5 2.1 A charger, so I should be fine correct?
Yes, BUT if you use a cheap Micro USB cable, NO.
Don't judge Linux by the Pi.......
I must not tread on too many sacred cows......

hippy
Posts: 8537
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 4:37 pm

Not sure what the actual USB Spec says but Farnell as an example say their "Micro-USB connectors meeting requirements of USB 2.0 Standard" are specified as -

1 A (per contact) or
1.8 A (contacts No. 1 and 5) and 0.5 A (contacts No. 2, 3, and 4)

http://www.farnell.com/datasheets/81390.pdf

I would expect that reflects the minimum the USB spec calls for though the microUSB socket used on the Pi could be rated better than that.

User avatar
DougieLawson
Posts: 40177
Joined: Sun Jun 16, 2013 11:19 pm
Location: A small cave in deepest darkest Basingstoke, UK
Contact: Website Twitter

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 5:55 pm

ktb wrote:I was warned that even the momentary rainbow-square on boot that fades away is a problem. I'm not sure I believe it. I seem to recall someone mentioning a spike at boot is to be expected on the Pi2B. I see it with a decent 2A Samsung charger.
My A+ (with a good supply) briefly gets the power square during boot (as the USB devices get enumerated) it's connected with WiFi at the moment (because I need to rebuild the kernel to use my SPI ethernet).
Criticising any questions is banned on this forum.

Any DMs sent on Twitter will be answered next month.
All fake doctors are on my foes list.

Note: Any requirement to use a crystal ball or mind reading will result in me ignoring your question.

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 13370
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 6:39 pm

ktb wrote:I was warned that even the momentary rainbow-square on boot that fades away is a problem. I'm not sure I believe it. I seem to recall someone mentioning a spike at boot is to be expected on the Pi2B. I see it with a decent 2A Samsung charger.
Which "momentary rainbow-square on boot" do you mean, the big one even before Linux starts booting? That one in itself has nothing to do with "showing a brownout", (power problem) unlike the tiny rainbow square in the right hand top corner of the GUI screen which does, those two "rainbow squares" have nothing to do with each other. The first one is actually the result of a test the GUI does, before it even turns on the ARM processor, the second one the desktop software shows as a reaction to a kernel message, that is created by the kernel, who looks at the brownout detector, and generates a message when it sees a brownout (a dip in VCC below 4.65V +- 0.05V).

Its very confusing that the desktop also shows a rainbow square, it would have been better to show a blue (or other colour) square. BTW. A red square means there is an over-temperature warning from the kernel (hotter than 85 degrees, so turning off overclocking).

ktb
Posts: 1447
Joined: Fri Dec 26, 2014 7:53 pm

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 6:47 pm

mahjongg wrote:
ktb wrote:I was warned that even the momentary rainbow-square on boot that fades away is a problem. I'm not sure I believe it. I seem to recall someone mentioning a spike at boot is to be expected on the Pi2B. I see it with a decent 2A Samsung charger.
Which "momentary rainbow-square on boot" do you mean, the big one even before Linux starts booting? That one in itself has nothing to do with "showing a brouwnout", as the tiny rainbow square in the right hand top corner of the GUI screen does, those two "rainbow squares" have nothing to do with each other. The first one is actually the result of a test the GUI does, before it even turns on the ARM processor, the second one the desktop software shows as a reaction to a kernel message, that is created by the kernel, who looks at the brownout detector, and generates a message when it sees a brownout (a dip in VCC below 4.65V +- 0.05V).

Its very confusing that the desktop also shows a rainbow square, it would have been better to show a blue (or other colour) square. BTW. A red square means there is an over-temperature warning from the kernel (hotter than 85 degrees, so turning off overclocking).
I'm not talking about the big rainbow box (I thought that was the splash screen?)
I'm talking about the small square in the upper right hand corner of the screen. It appears briefly as the console output begins to appear and fades away. I don't ever see it at any other time. This happens whether overclocked+overvolted or not. I use a 2A power supply from a Samsung tablet with a 26AWG USB cable leading to the Pi's micro USB port.

Edit: I also have two powered USB hubs connected. One hub supports wifi, bluetooth and the main data/power cable to an external drive and the other hub is just supporting a keyboard, mouse, cooling pad and the secondary power cable for the external drive which is connected to the other hub.

I'd like to try checking the test points on the Pi2B once I have confirmation of what they are labeled. Thanks for the information.

joseaplaza
Posts: 2
Joined: Thu Feb 05, 2015 9:06 am

Re: Power Requirements For A RPi2?

Thu Feb 05, 2015 7:38 pm

Well, having been testing the Pi2 since yesterday, and i can tell you the power requirements are definitely higher than the B+. I had no problems to power the B+ from one of the USB ports from my D-Link 7-ports usb, and it has turned out to be impossible with the Pi2. Sometimes it doesn't boot, sometimes it hangs after a couple minutes (with some error about the kernel).

Powering the Pi2 with a 2-amp samsung phone charger, it runs flawlessly. On the bright side, the performance is quite impressive, better than i was hoping for, and i haven't gotten any of the infamous "net_ratelimit: callbacks suppressed" that filled up my filesystem anytime i threw a little bit of load on the B+.

ktb
Posts: 1447
Joined: Fri Dec 26, 2014 7:53 pm

Re: Power Requirements For A RPi2?

Sun Feb 08, 2015 10:09 pm

ktb wrote:
mahjongg wrote:
ktb wrote:I was warned that even the momentary rainbow-square on boot that fades away is a problem. I'm not sure I believe it. I seem to recall someone mentioning a spike at boot is to be expected on the Pi2B. I see it with a decent 2A Samsung charger.
Which "momentary rainbow-square on boot" do you mean, the big one even before Linux starts booting? That one in itself has nothing to do with "showing a brouwnout", as the tiny rainbow square in the right hand top corner of the GUI screen does, those two "rainbow squares" have nothing to do with each other. The first one is actually the result of a test the GUI does, before it even turns on the ARM processor, the second one the desktop software shows as a reaction to a kernel message, that is created by the kernel, who looks at the brownout detector, and generates a message when it sees a brownout (a dip in VCC below 4.65V +- 0.05V).

Its very confusing that the desktop also shows a rainbow square, it would have been better to show a blue (or other colour) square. BTW. A red square means there is an over-temperature warning from the kernel (hotter than 85 degrees, so turning off overclocking).
I'm not talking about the big rainbow box (I thought that was the splash screen?)
I'm talking about the small square in the upper right hand corner of the screen. It appears briefly as the console output begins to appear and fades away. I don't ever see it at any other time. This happens whether overclocked+overvolted or not. I use a 2A power supply from a Samsung tablet with a 26AWG USB cable leading to the Pi's micro USB port.

Edit: I also have two powered USB hubs connected. One hub supports wifi, bluetooth and the main data/power cable to an external drive and the other hub is just supporting a keyboard, mouse, cooling pad and the secondary power cable for the external drive which is connected to the other hub.

I'd like to try checking the test points on the Pi2B once I have confirmation of what they are labeled. Thanks for the information.
So, I don't have a good explanation, but I'm no longer experiencing this issue.

I installed a fresh copy of Raspbian using the latest IMG on the same 64GB microSD card I was using before and I no longer see the small colored square on boot when using my Pi2B. I'm using the same 2A Samsung power supply, the same 26AWG USB to microUSB cable, the same two powered USB hubs, the same external hard drive, the same keyboard, same mouse, same wifi adapter, same bluetooth adapter, same TV, same HDMI switch... Well, you probably get the idea. The previously installed version of Raspbian was from the 12/24/2014 release and had been upgraded to the latest release.

Return to “General discussion”