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I'd like to use the Raspberry Pi as a small server. My Linksys WRT610N router has a rear USB port and I'd like to use it to supply power to the Raspi. That way, the Raspi doesn't need to have a dedicated power supply!

Only two wires will be connected to the Raspi:

  • an Ethernet wire,
  • the USB power supply wire connected to the router's USB port.

Will the router's USB port be enough to supply power to the Rasperry Pi?

Thank you!

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Model A or B? Please note Model B uses more power –  ArchHaskeller Jul 25 '12 at 20:11
1  
I'm talking about model B. This page describes what the Rapberry Pi needs according to the model: Model A -> 300mA, Model B -> 700mA. –  Morgan Courbet Jul 25 '12 at 20:15

3 Answers 3

Be aware that the USB port the Raspberry Pi uses for power does not have the data wires connected at all so the Pi cannot negotiate power requirements with the USB host and this can cause all kind of strange behavior. See this forum post in which Liz herself (foundation member) chimes in on this. Worst case scenario for you is the Pi works for a while then the router's firmware decides to go into a power saving mode which cuts amperage over USB to 100mA and you experience completely unpredictable failures with the Pi. Check the Power section of USB's wikipedia page for more detailed information about when USB power could drop down to the basic 100mA output. This is also a problem with cheapo powered USB hubs which is why a lot of people on the Raspberry Pi forums say not to power the Pi from a USB hub.

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I agree - Use a dedicated power supply like htc charger. Its only a few bux of ebay with cable and it is actaully a recommend charger. Another drawback is that the RPI does not support Power Over Ethernet. DOH DOH DOH WHY? –  ppumkin Jul 31 '12 at 9:57

Your router's USB port is probably only for shared printing and NAS (network attached storage). In either case, it would be running devices that run off their own power supplies (such as printers and hard drive enclosures). Because of this, the port was probably designed to only deal with the low power needed to interface an already powered device.

TL;DR: Measure across + and - pins (see below) with an ammeter or multimeter in line with you're Raspberry Pi.

enter image description here

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1  
Most inexpensive home user level multimeters are fused at 350mA... so if you expect to measure 500-700mA depending on which power figure you want to meet then you're going to end up with a blown fuse. When supplying near maximum power many power supplies will experience a dip in voltage so measuring just the maximum amperage is insufficient without knowing the voltage at the same time –  Dan B Jul 25 '12 at 20:49
    
Lol I forgot to mention the voltage drop xD –  XAleXOwnZX Jul 25 '12 at 22:05
2  
I don't recommend measuring across the +/- pins with an ammeter - you'll short circuit it! Instead put the ammeter in line with your load. –  Alex L Jul 29 '12 at 8:49
    
If he has an ammeter and an RPi, i'm more than certain he'll have the basic knowledge of parallel/series circuits and potential difference/current –  XAleXOwnZX Jul 29 '12 at 14:52
up vote 2 down vote accepted

I measured the power consumption of my WRT610N router with a Belkin Conserve Insight power monitor.

The WRT610N has two antennas (2.4GHz and 5GHz), and I disabled one of them. To load the system, I used sysbench --test=cpu --cpu-max-prime=20000 run.

                       +-------------------+------------------+
                       |                   |  RPi connected   |
                       | RPi not connected +------+-----------+
                       |                   | idle | full load |
+----------------------+-------------------+------+-----------+
| 1 antenna activated  |              5.8W | 8.1W |      8.3W |
+----------------------+-------------------+------+-----------+
| 2 antennas activated |              6.6W | Did not measured |
+----------------------+-------------------+------------------+

The WRT610N power supply can provide 18W (12V * 1.5A), so it can manage the additional 2.5W consumed by the RPi.

My RPi is powered by my WRT610N since one month, and I did not noticed any problem.

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