birger
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 11:08 am

Can the RPi be powered through the USB 2.0 port? I saw a comment in the wiki that +5V from the micro USB was sent unfiltered to HDMI and USB, so I hope this means the RPi can also be powered from the ordinary USB port.

The reason I ask is that a 7-port hub on DX is getting some warnings because of a design flaw. When you connect the power supply to the hub it actually powers the host USB port as well. Hub's shouldn't do that. There should be a diode preventing it. Would this be the perfect hub for powering the RPi?

http://www.dealextreme.com/p/7.....sb-hub-678

(note that there are separate product numbers for the China, UK and US warehouses. Choose your preferred source)

hippy
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 11:36 am

birger said:


Can the RPi be powered through the USB 2.0 port?


It looks to me that there are two fuses ( top right of board ) on those port power lines and my gut feeling is they will be 100mA, so if that's the case, no, not without replacing or bypassing a fuse, and there may be other issues as well such as socket and track current carrying ability.

It may be possible to link the power line on the USB socket to the GPIO power and bypass any fuse that way.

It would be nice to have full details of the USB socket power circuitry but expect it will come in due course.

This is my understanding of the power arrangement ...

http://www.raspberrypi.org/wp-.....ESSPSU.gif

plugwash
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 11:58 am

Utimately we probablly won't know the full protection details until schematics are released but i'd think the worst case is you will need to bypass a protection component which probablly won't be too big a deal.

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reiuyi
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 12:00 pm

birger said:


The reason I ask is that a 7-port hub on DX is getting some warnings because of a design flaw. When you connect the power supply to the hub it actually powers the host USB port as well. Hub's shouldn't do that. There should be a diode preventing it. Would this be the perfect hub for powering the RPi?


All hubs do this, there are never diodes in a usb hub. Regular computers have proper USB ports which do have this protection. The fact raspi doesn't have this is an advantage rather than a flaw. To answer your question; yes, you can power raspberry pi from 5v pin, micro usb, usb 2.0.. even hdmi if you're desperate. From a design perspective, it makes no difference where power comes from when it all shares the same cable (called a rail). Just like you can plug your tv in whatever wallsocket you wish, you can plug power into whatever suitable raspberry 5v connector you can find

Also please note that many cheap usb-hubs from the internet (China) are either USB 1.1 or extremely slow usb 2.0. If I were you I'd just buy it locally. For €10 you can just as well buy it in your local computer store, where you can actually return it if it's showing defects.

hamjudo
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 1:43 pm

The USB device ports are limited to 500mA.

The power port is current limited at 1000mA.

The Pi uses a few hundred mA by itself.

You can backpower the Pi through one of the USB device ports, however it means there won't be the full 500mA available through the other USB port. Which shouldn't be a problem, because you can plug the power hungry peripherals into ports on your USB hub.

hippy
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 1:44 pm

DeliciousRaspberryCake said:

From a design perspective, it makes no difference where power comes from when it all shares the same cable (called a rail).
For a single rail that is correct but on the R-Pi there are at least two rails ( and my guess is four ), all notionally +5V, but separated by fuses. The fuse ratings dictate what current can be passed in to any rail and made available for the other rails.

For example, if the USB ports do have 100mA fuses you can't pass the 600mA the R-Pi needs to run through that.

birger
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 2:02 pm

What I have read on the net suggests the opposite. That powered USB hubs normally provide power only to downstream ports, not to the upstream (host) port.

From my readings there should be a diode connecting +5V from the upstream port so that current will flow from the upstream host only if there is no local power supply on the hub.

I will wait until I am certain there are no fuses between the RPi USB port and the micro USB (power) port.

All feedback on that hub suggests that it is a high quality item except for that one 'problem' that iMacs supposedly don't like. A problem that could be a great thing for us.

plugwash
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 2:17 pm

DeliciousRaspberryCake said:


All hubs do this


BULLSHIT The USB 2.0 spec explicitly states

"No device shall supply (source) current on VBUS at its upstream facing port at any time. From VBUS on its
upstream facing port, a device may only draw (sink) current."

Of course there are a large number of devices (including the pi) that don't follow USB specs.

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reiuyi
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Re: power RPi through the USB 2.0 port?

Tue Jan 24, 2012 11:03 pm

plugwash said:


Of course there are a large number of devices (including the pi) that don't follow USB specs.



There are no devices that follow the USB specifications. rail isolation and current limiting would basically require a microcontroller for each USB port. No manufacturer in his right mind would spend this much effort on a PSU design. Due to this abandonment of the spec, we are able to connect a 2.5inch drive to our computer/tv/whatever.

hippy said:


blabla


Please see (and look up polyfuse):

hamjudo said:


The USB device ports are limited to 500mA.

The power port is current limited at 1000mA.

The Pi uses a few hundred mA by itself.

You can backpower the Pi through one of the USB device ports, however it means there won't be the full 500mA available through the other USB port. Which shouldn't be a problem, because you can plug the power hungry peripherals into ports on your USB hub.


hippy
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Re: power RPi through the USB 2.0 port?

Wed Jan 25, 2012 12:24 am

DeliciousRaspberryCake said:

hippy said:

blabla


Please see (and look up polyfuse):


Perhaps you'd be courteous enough to explain what in my earlier comment you have a problem with? If you believe something is incorrect then perhaps you could tell me what that is?

birger
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Re: power RPi through the USB 2.0 port?

Wed Jan 25, 2012 9:11 am

I have ordered one hub. Hopefully I can order my RPi as well soon.

Gaz99
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Re: power RPi through the USB 2.0 port?

Wed Jan 25, 2012 4:33 pm

Hi,  hopefully this will be of interest (to UK peeps anyway), excuse if this is off-topic, this is my first post.

Came across this company [ I have no commercial relationship with them - just saw an advert ] and thought it might be of interest some Raspberry PI owners

http://www.axmanufacturing.co.uk/

they make USB transformers that fit in a faceplate that fits in a standard UK double plug socket.  Thought it would be a neat way of powering a RPI and use the standard plug for the monitor.  They seem to have a 1A rating also.

the double USB version (just like the PI  ) doesnot seem to be available yet.

Looking forward to getting a RPI and hacking it

Jaseman
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Re: power RPi through the USB 2.0 port?

Wed Jan 25, 2012 4:43 pm

I still want to know if I can unplug my PS3 controller and power it off that?

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