Rev 2 and powered hubs - pi powered via micro-usb

[nooryani84]

So I have been reading a lot online, trying to figure out if my Rev 2 board can safely be powered via its own microusb on a 2A PSU while connected to a hub with 1-3A. The concept of backfeeding is a relatively new concept. Will my Pi risk backfeed and is this something i should worry about?

I've been looking at this http://www.adafruit.com/products/961 and considered getting one though I'm still worried about the backfeed issue. Can someone help me out here?

[wirelessmonk]

Almost an identical setup here. I say almost because I am powering the RPi through the hub as well as expanding the USB ports. I haven't encountered any issues to give me pause.

You can also cut the red wire. By that I mean cutting into the insulation of the USB A cable between the hub and RPi and snipping the 5v (red) wire. I did this with a connection to an Atrix lapdock before I began using the hub and never had any problems afterward.

As in all things, YMMV.

[Lob0426]

The USB standard states that hubs should not be able to back-power (back-feeding). The best way to find out if your hub is back-powering is to plug the RasPi into the hub, then plug the hub in, with no power connection to the RasPi. If the red light comes on, on the RasPi then you are having a back-powering issue with the hub. If no light comes on then you are not.

Normally USB hubs do not back-power the RasPi. If it does then you can either modify the cable to stop the back-power or just back-power the RasPi with no power cable at all. another situation that does not seem to cause problems is if you are power the RasPi with a USB A to micro B cable and the hub just happens to back-power the voltage is from the same source so should not cause you a problem.

My website is hosted on a "back-feeding" hub as the power source and I have had no issues with it. It has been up for more than 10 months this way. The only caveat is that I would make sure there is voltage protection built into the hub itself. My hub/s have a 2A polyfuse in them.

There is more on back-powering on my website.

[pjc123]

I have the following hub and it is specifically designed not to backfeed. It has a separate mini-usb port and cable to connect to the pi's USB data ports; I am sure all they did was not to feed power through this special port. Why buy a hub that you have to butcher later on (or modify a cable) when it is already done for you? It is also a 7 port hub and has a 3 amp power supply, and it is available on Amazon with excellent reviews from others as well. Now to answer your original question. Yes, this Plugable hub can be used with a separate power supply via the micro-usb port while at the same time connecting the hub to the USB data ports, and in fact I emailed the manufacturer that exact same question to double check before I bought it. However, for the pi I am using it with at the moment, one of the hub's regular usb ports supplies my pi with enough power:

http://plugable.com/products/USB2-HUB-AG7

[FTrevorGowen]

FWIW over the last year I've been investigating and testing a number of "low to moderate cost" USB hubs that may be powered (ie. not always supplied with a PSU) and possible PSU's for them and the Pi. The details can be found at http://www.cpmspectrepi.webspace.virgin ... BHubs.html and http://www.cpmspectrepi.webspace.virgin ... plies.html (and within further pages linked to from those). Roughly half of the hubs "provided" back-power (which, strictly-speaking, is not in accordance with USB hub specs.) Virtually all of them had the "power connections" of their, usually, four ports connected in parallel which means that they are unsuitable for use with "y-cable connected" HDD's or HDD caddies (see comments at http://www.cpmspectrepi.webspace.virgin ... vices.html. Personally, I'd recommend that only "externally powered" HDD's or HDD caddies are used with the Pi.)
Trev.

[Lob0426]

All USB hubs are not supposed to back-feed (back-power). Most hubs are supposed to be able to receive power from the computer.

I have had no problems running the 2.5" HDD's from a Y cable on my USB hubs. Most of these HDD take about 4 to 5 watts to start but run at 3 watts or less. The hubs that have high power charging ports will usually run single cable 2.5" drives. These are the travel size laptop drives that sell everywhere.

Back-feeding can be used to advantage if you are willing to do just a little research. There have also been a few people that cheated and ran the 5V and GND wires from their hub the the regular power connector so it was not back-powering at all. And some others have soldered two wires from the power port to the USB data ports and used a A to micro B cable into the power port.

The Raspberry Pi can be pretty versatile when it comes to supplying power to it!

[nooryani84]

Thanks for the responses! I checked out your blog and it's made things a lot clearer.

So the Adafruit hub seems like a great choice! However, I'm going to try avoid using a HUB for the time being as it somwhat takes away from the appeal of the raspberry pi when using it as a media center.

[FTrevorGowen]

...
I have had no problems running the 2.5" HDD's from a Y cable on my USB hubs. Most of these HDD take about 4 to 5 watts to start but run at 3 watts or less. The hubs that have high power charging ports will usually run single cable 2.5" drives. These are the travel size laptop drives that sell everywhere.
...

Unfortunately I've had the "opposite" experience. However, my "best hub", which does not back-power, manufactured by one of the originating companies of "USB" and meets the original, USB 2.0 specs, does not provide the newer, charging ports. I agree that hubs that do so, should be fine with Y cables and newer, low-power 2.5" HDD drives. My "stringent" measure of "Y cable support" is whether a CD/DVD drive, originally supplied with a MEDION laptop and filtered Y cable works. 3.5" HDD caddies/drives usually need 12V as well as 5V (may be derived internally) and are usually externally powered anyway. For me cost is also an issue - so far all of the hubs with charging ports I've found so far cost more than the Pi itself.
Trev.

[Lob0426]

3.5" Drives with enclosures generally come with their own PSU and have no problem working with the Raspberry pi. The problem children are the 2.5" drives that are powered from the USB only. My hub only supplies 500ma per port and works just fine with a USB to SATA adapter that includes a "Y" cable. It will not work directly from the RasPi at all, (I have occasionally got it to work but it does not last long) but it works on every hub I have tried so far.

I have even used it to provide the back-power to the RasPi. I plugged the Data/Power cable into the RasPi and then plugged the power only USB port into an iPad charger (5V 2.1A). Worked well, the only problem is there is no real overvoltage protection with that setup. There is a picture of it operating on my website if you do not happen to believe me. Your adapter may be a little pickier or your HDD might draw a little too much for proper operation.

I have used mostly Seagate 120GB and 320GB laptop drives. My Lapdock uses a bone stock 640GB Free Agent with the supplied single cable and works like a charm. I also have used a Toshiba 1TB drive. I have used those hubs to run a USB DVD-RW (bought from Wal-Mart) drive that uses a single port USB cable with no problems.

None of my hubs supplied back-power from the manufacturer. I had to make them back-power. They worked with the USB HDD adapter either way. 1 stock and two modified to back-power (back-feed)

The USB to SATA adapter I am using is below;
http://www.newegg.com/Product/Product.a ... 6812816095

The hub is here;
http://www.newegg.com/Product/Product.a ... 6817111831
Its factory specs state it is for less than 500ma per port.

I hope this helps you out!

[rom232]

hello, I have the following problem. my external hdd is not being detected. although the external case may be. I use a powered hub connected to raspberry with a modified cable (red wire).

dmesg seems to detect, but not boot the hd. aluguma idea?


(Sorri, Google translate.)

[RTD1]

I have a D-Link DUB-H7 that I use to power my Pi (I connect a cable straight from one of the hub's powered USB ports to my Pi's micro USB power connect) with zero issues. No problems at all and one less cable/PS to worry about.

[Lob0426]

I have a D-Link DUB-H7 that I use to power my Pi (I connect a cable straight from one of the hub's powered USB ports to my Pi's micro USB power connect) with zero issues. No problems at all and one less cable/PS to worry about.

That is how most people power their RasPi's from a hub. The main advantage of back-powering is that you only have one USB cable connected. The uplink cable. Where you have one to uplink and one as a power. So a four port hub is reduced to three ports, plus one port on a B model RasPi. I have four ports plus the extra on the RasPi.

This really only an advantage if you need to have less clutter around your RPi. The other is that I was able to power two RasPii from the hub and have three ports left on the hub. Only one RPi had access to the hub.

Back-powering is not for everyone, but it has advantages and disadvantages of its own!