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Re: Potential power source

Posted: Sun Apr 01, 2012 9:01 am
by Phil Spiegel
I've bought  reels of 0.81mm OD 7/0.1mm which is rated  at 4 Amps!

(And it's not dodgy chinese manufacture or April 1st -even if it is), but form one of our RPi distributors ....

..its because its silver plated and PTFE sleeved so its the current capability at 200C!

I only plan using it for < 20mA though! (PVC sleeving would be for 60C and perhaps 0.4A?)

Re: Potential power source

Posted: Sun Apr 01, 2012 11:28 am
by elsleepy
can I use this minipak from horizonfuelcell its 5 volt out but don't find the A?


http://www.horizonfuelcell.com.....inipak.htm

Re: Potential power source

Posted: Sun Apr 01, 2012 11:44 am
by john_wage
elsleepy said:


can I use this minipak from horizonfuelcell its 5 volt out but don't find the A?


http://www.horizonfuelcell.com.....inipak.htm


The product description says 5 Volts up to 2W

Ampere = Watt / Volt

2W / 5V = 0.4A or 400mA

so no

Re: Potential power source

Posted: Mon Apr 02, 2012 5:11 am
by Jim Manley
The R-Pi board allegedly draws 200 ma with nothing else connected. Add a USB keyboard and mouse and you should still be below 400 ma. You won"t be able to power any other USB devices unless they come with their own power supply (e.g., an external USB hard disk drive), or you connect a powered (active) USB hub, which will also provide four, or more additional USB ports.

Re: Potential power source

Posted: Mon Apr 02, 2012 6:58 am
by john_wage
I wouldn't gamble on a weak power source, if your PSU at any one time even for a very brief moment comes up short of the demanded power your system will crash I guarantee it.

Re: Potential power source

Posted: Mon Apr 02, 2012 8:16 pm
by arm2
Jim Manley said:


The R-Pi board allegedly draws 200 ma with nothing else connected.


Then ask it do something and it reportedly draws up to 500mA(2.5W) Model A & 700mA(3.5W) Model B. Interestingly that is the wiki but not the FAQ though I'm sure it has been stated authoritvely quite a few times. This is excluding any power being drawn from the USB ports as 300mA has been stated as available before the 1Amp input fuse would blow.

Re: Potential power source

Posted: Mon Apr 02, 2012 10:11 pm
by pygmy_giant
oh – thats ok! 600ma should be enough for a dinky robot with nothing else attached except some solid state relays…. cant believe I got all 6 for 99p each – they"re £5+ on the net…. tempted to resell them on ebay for £7 and make a 700% profit! I think the shop staff must have put the wrong lable on as they were next to the nds silicone cases at the same price in similar packaging.

Re: Potential power source

Posted: Tue Apr 03, 2012 9:06 am
by hippy
Jim Manley said:


The R-Pi board allegedly draws 200 ma with nothing else connected.


700mA for Model B

500mA for Model A

According to the Wiki - http://elinux.org/Rpi_Low-leve.....eripherals

Re: Potential power source

Posted: Tue Apr 03, 2012 9:39 am
by Chris.Rowland
Using a weak power supply on a computer is a recipe for intense frustration.

As people have said if the power drops, even for an instant, memory and processors get corrupted.  If you are lucky it will crash, if not it will continue to work but with random code or data changes. This gives all sorts of inexplicable and inconsistent errors.

Re: Potential power source

Posted: Tue Apr 03, 2012 9:51 am
by pygmy_giant
Hmmm.... I know the feeling - thats what I'm like at the end of the working day. If my lipo's don't cut it I'll use them to power secondary circuits. I'm not sure any of us can be certain of the 700mA figure until its been tried and tested in different contexts. Would I be right in interprating it to mean 700mA to power standard periferals such as keyboard, mouse and hdmi out?

Re: Potential power source

Posted: Tue Apr 03, 2012 12:27 pm
by john_wage
@pygmy_giant

yes most likely when they came out with the 700mA recommended figure they would have taken in consideration the standard peripherals and then some.

Re: Potential power source

Posted: Tue Apr 03, 2012 1:12 pm
by pygmy_giant
your avatar pic reminds me of the mad nuclear scientist in th 80's film Repo Man.

Re: Potential power source

Posted: Tue Apr 03, 2012 1:34 pm
by john_wage
it's Duke Nukem

Re: Potential power source

Posted: Wed Apr 04, 2012 5:04 am
by Subterranean
My plan is to replace the regulators with some switched mode ones and make a li-ion battery pack with the 18650 cells that go into laptop batteries. Should keep me going for a decent amount of time but I'll be interested to see what sort of power decrease good efficiency regulators will bring. May look at powering a small screen with the battery pack as well, we'll have to see.

Re: Potential power source

Posted: Wed Apr 04, 2012 6:04 am
by Jim Manley

Jim Manley said:

The R-Pi board allegedly draws 200 ma with nothing else connected.


hippy said:


700mA for Model B

500mA for Model A

According to the Wiki - http://elinux.org/Rpi_Low-leve.....eripherals


hippy,
500 and 700 ma are the maximum current ratings for the A and B boards, not minimum draw, which is 200 ma AIUI.

Re: Potential power source

Posted: Wed Apr 04, 2012 6:53 am
by Ice
http://www.qoqa.fr/fr/offer/3165 

I've found this and I thinks it will be fine with raspberry pi but I'm not sure...

Re: Potential power source

Posted: Wed Apr 04, 2012 8:40 am
by john_wage
Jim Manley said:


500 and 700 ma are the maximum current ratings for the A and B boards, not minimum draw, which is 200 ma AIUI.


Exactly, and when you design your power supply it MUST be able to cope with the maximum peaks that the system could possibly draw, otherwise you get catastrophic results.

Re: Potential power source

Posted: Wed Apr 04, 2012 9:58 am
by Jim Manley
Jim Manley said:


500 and 700 ma are the maximum current ratings for the A and B boards, not minimum draw, which is 200 ma AIUI.

john_wage said:
Exactly, and when you design your power supply it MUST be able to cope with the maximum peaks that the system could possibly draw, otherwise you get catastrophic results.


In general, designing for the max current is definitely advisable. Some of us will be running R-Pi boards in headless mode (e.g., SSH/VNC in via network, no video out, no keyboard/mouse, etc.), so, we can design for lower supply current, which will be important for parallel-processing Brambles of large numbers of R-Pi boards.

Re: Potential power source

Posted: Wed Apr 04, 2012 10:47 am
by matthew1471
I'm planning on using my pi as a media player with xbmc (or something similar), so it'll be sat next to my existing TV setup.

I checked the back of my Sky+HD box last night and there's a USB port - does anyone have a meter they could use to check the output? It would be great if it's got enough beans to power the pi!

Re: Potential power source

Posted: Wed Apr 04, 2012 10:59 am
by pygmy_giant
you can get multimeters from ebay quite cheaply...

Re: Potential power source

Posted: Wed Apr 04, 2012 11:08 am
by hippy
matthew1471 said:

I checked the back of my Sky+HD box last night and there's a USB port - does anyone have a meter they could use to check the output? It would be great if it's got enough beans to power the pi!
Not necessarily easy to do as it might mean destructive testing; you would have to put a known load on the USB supply pins and see what happens. A 5W 5R resistor should do the job to test 1A current draw. Note that how it behaves short term may not be how it behaves long term with 24/7 usage.

You'd really have to get Sky to comment on its USB power supplying capabilities, see what it says in the user manual, reverse engineer the circuitry, or hope someone has a spare Sky box which they don't mind risking destructive testing on. Different box models may behave differently.

Re: Potential power source

Posted: Wed Apr 04, 2012 5:48 pm
by Jim Manley
Nowadays, such ports are generally load-protected and if they can"t provide the needed current, they just shut down until the load is removed (I wouldn"t leave anything plugged in any longer than needed to determine whether everything was OK). However, according to the USB spec, the minimum current load a USB port has to support is 100 ma (if power is provided at all), and the most is 500 ma, so, even if the port does provide 500 ma, that"s awfully close to what the R-Pi with a keyboard and mouse/trackpad will likely draw, and if the port only provides 100 ma, fuhgeddaboudid.

Re: Potential power source

Posted: Wed Apr 04, 2012 6:31 pm
by matthew1471
Ok, thanks for the input!

I'll take the advice and not worry about it... I don't want to blow up my Sky box

Re: Potential power source

Posted: Wed Apr 04, 2012 9:50 pm
by Matrix
Would this be any good folks,

http://www.amazon.co.uk/Energy.....038;sr=8-1

Re: Potential power source

Posted: Wed Apr 04, 2012 11:22 pm
by mahjongg
Matrix said:


Would this be any good folks,

http://www.amazon.co.uk/Energy.....038;sr=8-1


Cheap chargers have a tendency to be badly regulated, and sometimes will output more than the (generally) maximum acceptable voltage of 5.0V + 5% = 5.25V.

That is acceptable for many charging inputs, but not for devices that want regulated 5V power, like the R-PI.

But this one seems to be OK, as it claims to be regulated to 5.2Volt.