Featured Articles
Announcing Pi
Technical Specifications
Raspberry Pi FAQs
Win a Pi
Raspberry Pi Wishlist
Actions
Forum Thread Details
  • State Verified Answer
  • Replies 15 replies
  • Subscribers 709 subscribers
  • Views 2895 views
  • Users 0 members are here
Related

Does RPi B+ have high enough power output?

e14 Contributor

I have just bought a RPi B+ and found it cannot power my WD My Passport 1TB USB3 drive. The drive just clicks rather than spins up.

 

I'm hoping that it is something I ma doing wrong. Do all the USB ports on the B+ provide the same power?

Parents
  • 0

    The 'pi has, just as the Michael says all the ports wired in parallel.

     

    The revision one had two extra polyfuses in the 5V lines going to the USB ports. Those were supposed to currentlimit them to about 100mA. But that was a long time ago. The current "B" is very similar to the B+, except that it has a polyfuse that is one notch smaller.

     

    I've done some measurements on a "classic B". When the 5V drops too low the first thing that fails is the LAN9512. On the 'B this happened when the voltage on the 5V dropped below 4.3V. It is entirely possible that the raspberry pi B+ will continue to run down to about 3.0V: The LAN chip (which is also USB HUB) is the main consumer of the 3.3V. The lan chip will tolerate 3.3V +/- 10%, so at  3.0V it will continue to work. But below that it fails. The CPU also runs off the 5V line... But it too tolerates voltages down to at least 3.0V. So apart from the CPU and the 3.3V regulator is there anything else that uses 5V? Well, yes: The HDMI provides 5V for self-powered converters. And USB.

     

    So, assuming the polyfuse is creating your trouble, you can try to power your raspberry pi "behind" the fuse. i.e. on the GPIO header or on the USB connectors. So what usually works is to have a powered hub and let he lead to the hub power the 'pi too. But that still has the bulky hub in your system...

     

    One other thing you can try: Plug the power-plug of your harddrive into that 2A powersupply..... See what happens.

    (First I'd like to see the disk spin up. Then when you plug the dataplug into the raspberry pi, I'd like to see the 'pi power up as well... )

Reply
  • 0

    The 'pi has, just as the Michael says all the ports wired in parallel.

     

    The revision one had two extra polyfuses in the 5V lines going to the USB ports. Those were supposed to currentlimit them to about 100mA. But that was a long time ago. The current "B" is very similar to the B+, except that it has a polyfuse that is one notch smaller.

     

    I've done some measurements on a "classic B". When the 5V drops too low the first thing that fails is the LAN9512. On the 'B this happened when the voltage on the 5V dropped below 4.3V. It is entirely possible that the raspberry pi B+ will continue to run down to about 3.0V: The LAN chip (which is also USB HUB) is the main consumer of the 3.3V. The lan chip will tolerate 3.3V +/- 10%, so at  3.0V it will continue to work. But below that it fails. The CPU also runs off the 5V line... But it too tolerates voltages down to at least 3.0V. So apart from the CPU and the 3.3V regulator is there anything else that uses 5V? Well, yes: The HDMI provides 5V for self-powered converters. And USB.

     

    So, assuming the polyfuse is creating your trouble, you can try to power your raspberry pi "behind" the fuse. i.e. on the GPIO header or on the USB connectors. So what usually works is to have a powered hub and let he lead to the hub power the 'pi too. But that still has the bulky hub in your system...

     

    One other thing you can try: Plug the power-plug of your harddrive into that 2A powersupply..... See what happens.

    (First I'd like to see the disk spin up. Then when you plug the dataplug into the raspberry pi, I'd like to see the 'pi power up as well... )

Children
No Data