Don't "wait and see what happens" - just ask! :)

Okay, I'll just ask!

     As my name suggests, I may be among the oldest members of this discussion.  I am certainly among the most inexperienced, i.e., I have none.

     I have just purchased an RPi  -- oh yes, I went to school there 50 years ago --  . 

     After doing a reasonable amount of research, I selected the Manhattan 7port powered USB hub from Adafruit, in addition the the "starter package" micro USB power adapter.

     NOW, I read about the backfeeding issues some are experiencing. Will the extra money I spent on the Manhattan "protect" me from backfeeding?

     Your advice will be appreciated.

     Regards,

     The oldman

Okay, I'll just ask!

     As my name suggests, I may be among the oldest members of this discussion.  I am certainly among the most inexperienced, i.e., I have none.

     I have just purchased an RPi  -- oh yes, I went to school there 50 years ago --  . 

     After doing a reasonable amount of research, I selected the Manhattan 7port powered USB hub from Adafruit, in addition the the "starter package" micro USB power adapter.

     NOW, I read about the backfeeding issues some are experiencing. Will the extra money I spent on the Manhattan "protect" me from backfeeding?

     Your advice will be appreciated.

     Regards,

     The oldman

Harry Strock wrote:

 

     I have just purchased an RPi  -- oh yes, I went to school there 50 years ago --  . 

     After doing a reasonable amount of research, I selected the Manhattan 7port powered USB hub from Adafruit, in addition the the "starter package" micro USB power adapter.

 

     NOW, I read about the backfeeding issues some are experiencing. Will the extra money I spent on the Manhattan "protect" me from backfeeding?

Back-feeding (or back-powering) was a frequent problem with RasPi Model B rev 1.0, but with the rev 2.0 board (the ones with "mounting holes") it's usually not an issue.  According to the USB spec, a USB hub is not supposed to provide upstream power.  My cheap Inland hub has a Schottky diode to prevent this, some hubs have a jumper or small switch to prevent upstream power, and I suppose some high-end hubs use hot-swap circuitry.  However, a lot of hubs simply disregard the spec and just connect Vbus to all ports, whether they're downstream or upstream.

The reason this was a problem with the original RasPi Model B is that it had 140 mA fuses for the two USB ports to protect RasPi from rogue USB devices.  However, a non-compliant externally-powered hub would happily power RasPi through the 140 mA fuse.  140 mA was enough to get RasPi's boot process started, but as more of the SoC powered up there was soon too much current for the 140 mA fuse and it would trigger, stopping the boot process mid-stream.  This would cause RasPi to halt and stop using much power, so the fuse would recover and then do it all over again.  Aborting the boot process over and over is a great way to corrupt the SD card, so the RasPi forum got lots of complaints about this.

Well, one approach would be to tell people they'd have to use compliant hubs that don't back-power.  This is a nightmare, because as you know it's really hard to tell whether a given USB hub is compliant or not.  So RasPi decided to get rid of the USB fuses, first replacing them with 0 Ohm jumpers and then omitting them entirely on rev 2.0.  This means that if your USB hub can back-power, it will do so and the USB hub voltage will go to RasPi's 5V plane with no protection other than thickness of USB cable wires any fuses in the USB hub.  While this is less safe, I haven't seen examples of people killing the RasPis this way so overall it's been an improvement over rev 1.0, except that now the USB ports on RasPi modem B rev 2.0 aren't hot-swappable.  Well, can't expect everything for US$35.

Here's how you can tell if Manhattan back-powers: unplug your Micro USB power supply and see if RasPi boots up with just the Manhattan.  If that works, you can store away your Micro USB power supply and simplify your cabling.

I always use my RasPi model 1.0 with an Atrix Lapdock, which deliberately back-powers its USB upstream connection.  I replaced my 140 mA USB fuses with 1.0 A fast blow surface mount fuses and it works great -- I only need a single cable for USB data and 5V power.

For more information on the history of all this, I suggest this thread: http://www.element14.com/community/thread/19316.

Also, for RasPi questions you're best off posting at the RasPi group: http://www.element14.com/community/groups/raspberry-pi.