Featured Articles
Announcing Pi
Technical Specifications
Raspberry Pi FAQs
Win a Pi
Raspberry Pi Wishlist
Actions
Forum Thread Details
  • Replies 31 replies
  • Subscribers 681 subscribers
  • Views 6840 views
  • Users 0 members are here
Related

Incompatible Self-Powered Hub

morgaine

[This thread was split off from an earlier general one about Powered Hubs and has been given a more appropriate subject line.  Note that replies prefix "Re:" to the old subject line.]

 

 

The Pi's very poor power design results in some perfectly good self-powered hubs being incompatible with it.  For example, the cheap little 7-port self-powered Dynamode USB-H70-1A2.0 hub that Farnell advertises as a Pi accessory:

 

 

is not actually Pi-compatible at all, because in addition to powering its 7 host ports, it also powers the Pi board through its A-B upstream lead yet is incapable of supplying enough power to do that successfully (the Pi's Vcc drops to well below 4V).  As a result, when the micro-USB is powered down but the hub is powered up and connected, the Pi ends up rebooting continuously every couple of seconds, potentially leading to destroyed HDMI displays among other worries.

 

So, buying a self-powered hub is not necessarily the end to your Pi power problems.

 

Really the Pi's power design needs to be nuked from orbit and redesigned from scratch.  It's just plain bad in numerous ways.

 

Morgaine.

Parents Reply Children
  • in reply to wallarug

    You failed to understand what was written.  Read it again.

  • in reply to wallarug

    Fergus Byrne wrote:

     

    Why would you power your RPi from a hub that is only designed to give a max current output 500mA?  This is asking for trouble.

     

    Just buy another power supply for the RPi.

    It's pretty hard to tell what a given hub was designed to do without taking it apart.  My Inland 4-port with upstream cable connects its 5V external power jack to all downstream ports directly, so all the 5V current could go to a single downstream port, limited only by PCB traces and iffy 3.5mm barrel connection.

     

    The advantage of powering RasPi from a hub is convenience -- you don't need an extra wall wart, and you don't have to worry about a powered hub erroneously trying to power RasPi through the hub's upstream port.