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Re: Only one Power Adapter

Posted: Sat Jan 21, 2012 11:25 pm
by MarshallBanana
Hi there,

first and foremost i found a lot of threads dealing with power supply and also screens, portability and so on, but i felt that none really touched what i was aiming at...

anyone having seen a display like the "GeChic On-Lap 1301"?
http://www.gechic.com/product.asp

it's a hdmi display getting it's power over a usb-cable...

because really i want a raspi with only one!!! power-adapter...

which basically means that either a) the RasPI has to provide power to the display or b) the display has to provide power to the RasPI.

from all the posts i have read i guess it will be quite hard to achive the requirements i've set for myself

1. working RasPI
2. keyboard
3. mouse
4. wifi
5. usable, portable display (portable as in backpack, usable as in 10" or above)
6. only one power-adapter

(7. not too expensive )

as the threads dealing with usb-power-issues seem to suggest that adding usb keyboard, usb mouse and usb-wifi will already quite strech the available usb power to the limit, i guess my aproach using a display like the one at the top will basically just not work, right??

so to wrap it up, my questions are:

a) did i get it wrong, could it actually work using the above mentioned display, usb-keyboard+mouse+wifi?

b) if so, has anyone suggestions as to other displays similar to the one above?

c) or does anyone know of a portable display having hdmi/dvi/composite input that can also provide power to the RasPI??

(i don't think the often mentioned displaylink usb devices will be a good solution as they are too hard on the system resources as far as i've read, and in the RasPI we don't have many of those *g*)

---- end of long post, thanx everybody

Re: Only one Power Adapter

Posted: Sat Jan 21, 2012 11:54 pm
by Tomo2k
That screen draws 1A at 5V.

"Host" USB ports (eg on your PC, on the RPi) can supply an absolute max. of 500mA.

On the RPi this is enforced by a polyfuse for each USB port, and the RPi PSU socket also has a 1A polyfuse.

Thus it cannot be powered by any "host" USB port, it can only be powered by the large USB PSUs.

You will able to do a "single PSU" method by using a USB PSU that has two USB charging ports, however you will need one with quite a large capacity - you will want 1A available to the RPi as well as 1A for the screen.

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 12:04 am
by Lynbarn
Nice screen! Available for £120 (inc VAT) so a bit OTT for a 'Pi, but it could also be used for other purposes. I'll add one to my wish-list. Thanks for finding it.

As for a PSU, would one of these do it for you?:

http://www.raspberrypi.org/for.....sainsburys

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 1:02 am
by MarshallBanana
@Tomo2k thanks for the quick answer and the explaination... i feared as much, but good to get confirmation by someone who knows his stuff...
but just to clarify i got it right: the B board uses up to 700mA, so a 1A PSU will leave 300mA to be consumed by the USB devices correct? so having usb keyboard, usb mouse and usb wifi, those three will have to stay below a power consumpiton of 300mA combined, correct?

@Lynbarn thanks. but that device seems to output only 500mA on each line, so i guess that won't work.
Searching around i found several devices that have 2 usb outputs, and a rating of 1000mA as output, but when connecting both lines only 500mA on each line. Or devices that have an output of 2 amps, so maybe would fry some components...

on amazon.de i found a "Belkin USB Charger DUO" for just under 10 euro which seems to do 1000mA on both ports, which would be ok.

so it seems i'd either have to a) go with the GeChic screen and this Charger, and have two cables connected to the PSU, b) find another screen that can be powered over the RasPI-USB-Port or c) find a screen that can also power the RasPI...

i still hope for b) as my plan is to build my own TeddyPuter:

Put RasPI in Teddybear + Connect all stuff directly into Teddy = pure awesomeness

so having a circle in there as both teddy and screen will be connected to psu instead of having a TeddyVerse with teh bear in it's center would somehow lessen the experience *g*

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 1:25 am
by abishur
Just to make sure people reading this thread are clear, the r-pi has a self resetting fuse that will trip when more than 1A of current is drawn.  This means that the r-pi will not be able to supply a full 500 mA across both usb ports.  You could replace the fuse with a higher Amperage one, but you'd end up voiding your warranty

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 12:26 pm
by specsdude
I plan to get something like this:

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

You just put in 4 AA batteries- rechargeables can be up to 2300 mAh at 1.2V x 4 that makes 4.8V and ~9-10 000 mAh!  Nice portable power solution for RPi.

Only drawback is that it only has 1 x MicroUSB output, unlike this:

http://www.amazon.co.uk/TeckNet®-Dual-P ... pd_cp_ce_1

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 1:25 pm
by dRay
Dave Seeber said:

You just put in 4 AA batteries- rechargeables can be up to 2300 mAh at 1.2V x 4 that makes 4.8V and ~9-10 000 mAh!  Nice portable power solution for RPi.

Unless you take 16 AA rechargeables you wont get 4.8V AND 9Ah, instead either/or with 4 rechargeables.

Re: Only one Power Adapter

Posted: Sun Jan 22, 2012 1:36 pm
by Point3Forever
If you're willing to do the work you could create the power supply yourself. I'm planning on powering a small screen (3.5") using a li-po battery (11.1v), and using a 5v regulator I made for the raspberry pi. This set-up will also be able to be powered with a wall wart.

Re: Only one Power Adapter

Posted: Mon Jan 23, 2012 4:18 am
by jwatte
Is the requirement "one power supply" like:

1) Only one wall plug? If so, you can use a single transformer that outputs more than one cable/voltage.

2) Only one cable from the wall plug to the integrated system? If so, you can use a 5V high-amperage supply in the integrated system (duct tape it on and split out 5V for the RasPi.

3) Only one power supply in some transcendental meaning? If so, I'd like a little more details on what that requirement actually means before I can say anything

Re: Only one Power Adapter

Posted: Mon Jan 23, 2012 10:43 pm
by lakyljuk
jwatte said:


Is the requirement "one power supply" like:

1) Only one wall plug? If so, you can use a single transformer that outputs more than one cable/voltage.

2) Only one cable from the wall plug to the integrated system? If so, you can use a 5V high-amperage supply in the integrated system (duct tape it on and split out 5V for the RasPi.

3) Only one power supply in some transcendental meaning? If so, I'd like a little more details on what that requirement actually means before I can say anything


I am planning to build HTPC from it, containing USB DVD and USB HDD.

I would like to power Pi and USB hub and 3,5" HDD from one power supply if this is possible. I was thinking about 3,5" HDD SATA USB adapter, which is  powered by 12V 5V 2A brick. Could it be possible double +5V and GND wires and put them into USB hub to power it? And than power Pi from this hub? Or would be better tripple those 5V nad GND wires from power supply and put it into USB hub and into Pi itself? Can any power supply handle this? If not, can someone suggest some better solution?


 

Re: Only one Power Adapter

Posted: Mon Jan 23, 2012 11:31 pm
by digital_addict
I can suggest only one option, and it's messy.

Take an old pc power supply, cut off the molex plugs, connect the 5volt lines to chassis mount usb sockets, and the 12volt lines to whatever socket that is appropriate. The whole thing would need to be boxed. As I said messy. There are 2 major faults with this plan. 1) Noise from the fan. 2) Power consumption. (and probably more) Advantages, one plug in the wall, and masses of watts.

Is this the type of thing you are looking for?

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 6:58 am
by lakyljuk
@digital_addict

Yes, kind of. This solution has one major disadvantage - power consumption. I would like to stay as low as possible, since Pi consumes 3W and USB DVD and HDD adds some more watts, I would like to have something like laptop power supply, which would provide 12V and 5V. Like I said, there are SATA->USB converters, which are powered and provides 12V and 5V @2A, but they are meant to power harddrive, I dont know if it can handle USB hub and Pi too at same time assuming I would tripple 5V rail and put it into USB hub and Pi. I know it would be less hassle to use 2,5" HDD which can be USB powered and stay with simple powered usb hub, which could power this HDD and Pi too. But I have some spare 3,5" HDD, so I need some power source able to output 12V and 5V at same time. Or is it possible to take only some good 12V power supply and with some resistors make it output 5V? Thanks for any ideas.

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 7:15 am
by limki
this may be a stupid idea, but how about taking a super powered USB hub (if there is a power supply higher than 2A):

connect it (IN) to rPi USB port for data and loop one of the (OUT) ports back to rPi as power source

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 8:45 am
by spamel
Not a stupid idea at all, it is what I intend to do and I see no reason why it won"t work. The hub is powered independently, you are nicking a bit of the power out of one socket to power the Pi. Just because the pi then connects via usb for data transfer from the other ports is irrelevant as the socket powering it has nothing to do with data transfer, or that is how I see it. Dunno if I explained that well!

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 8:51 am
by lakyljuk
limki said:


this may be a stupid idea, but how about taking a super powered USB hub (if there is a power supply higher than 2A):

connect it (IN) to rPi USB port for data and loop one of the (OUT) ports back to rPi as power source


Yes, this can be done. But usb hubs are powered by 5V. For my project I intend to use 3,5" usb hard drive, which needs 12V. It is complicated, so maybe easier would be get some 2,5" USB HDD and powered USB hub.

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 11:00 am
by DavidJBrown
HI all, first post.

I'm also looking to do something like this when the Pi is available.

What I'd like is to power a USB Hub, power the Pi from the hub and the attach the Pi USB out into the HUB to share out the USB ports (for Keyboard, Mouse, Wi Fi).

Would something like this work?

http://www.amazon.co.uk/High-S.....B003DVC7N6

In an ideal world I'd like to mount the Pi and a stripped down (without casing, just the PCB) USB Hub inside 1 case (pref. clear plastic) with all the ports available and 1 power IN.

Does this sound realistic? or am I aiming too high? Appriciate your thoughs.

D

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 11:25 am
by MattHawkinsUK
I just ordered a 12V to 5V converter from ebay for a few quid. Given it is on a little pcb with connectors I couldn't make one myself for that. Plan on doing some tests running a PI from a 12V 7ah lead acid battery or maybe a stack of 9V rechargeables.

The ebay seller also had a PIR module and a remote control relay module that I was tempted by. They look like they would be possible to integrate with the GPIO pins on the PI ... but I can always order those in the future.

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 1:54 pm
by rurwin
Something like this maybe?

Building a power distribution box would be a nice first project for someone just getting started with a soldering iron.


Or devices that have an output of 2 amps, so maybe would fry some components…


It's the voltage and the maximum current that matters. If the voltage is 5V then you will not fry anything, even if you have a 100A power supply. The RPi will take it's 0.7A, and the other kit will take say 1A, and there will be 98.3A left for anything else you want to connect. (In fact a 100A PSU would probably not regulate properly with such a tiny draw, so it might give more than 5V and fry the RPi, but that would not be an issue for a more reasonable one. For example the one I linked to above has a minimum current of 10mA.)

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 2:19 pm
by Chromatix
As an exercise, I pulled together a bunch of (mostly spare) equipment to set up an R-Pi with:

1) Any of several SD cards.

2) A HDMI-DVI adapter for one of my existing monitors.  I'm fairly sure I've also got one somewhere which can accept the Composite input - no TV in my flat.

3) A powered USB hub and it's PSU.

4) A MicroUSB cable from the hub back to the R-Pi's power socket - this I had to buy since my phones all predate the EU standard, and I actually had to look fairly hard to find one at a reasonable price.  Nokia wanted to sell me one for €30!

5) An Ethernet cable.

Since the Model B has two USB ports built in, and my DVI KVM switch handles both keyboard and mouse from one USB cable, I could also probably power it from my alarm clock (which has a phone charging attachment) and forego the USB hub.  This would still leave one USB port free for some random peripheral.

Now, off to pick up the shipment of SD cards which I've been waiting for.

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 2:54 pm
by beren
What about buying a simple but reliable usb hub with 0.5A per port

(http://www.amazon.co.uk/D-Link.....038;sr=8-1)

and getting a couple of Y usb cables??

(http://www.amazon.co.uk/Nexons.....038;sr=8-1)

would that work?

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 3:31 pm
by digital_addict
beren said:


and getting a couple of Y usb cables??

(http://www.amazon.co.uk/Nexons.....038;sr=8-1)

would that work?



You would also require one or more of these

http://www.ebay.co.uk/itm/Mini.....20c1a02299



Your cable has a mini plug on it, you need a micro plug for the R-Pi.

For what it's worth, this is the route I’m taking, my usb hub has a 3amp supply.

Re: Only one Power Adapter

Posted: Tue Jan 24, 2012 6:21 pm
by beren
digital_addict said:


You would also require one or more of these

http://www.ebay.co.uk/itm/Mini.....20c1a02299



Your cable has a mini plug on it, you need a micro plug for the R-Pi.

For what it's worth, this is the route I’m taking, my usb hub has a 3amp supply.


Wow, my bad. Thank you for noticing it! There are y usb A -> micro cables, so it should be easy.