Avoiding a powered USB hub

Using Arduino General Electronics
#1

Hi, This isnt really arduino realted, although one is used in the end scpe of the project. I want to power a device which normally needs external power without using a powered usb hub.

its an external hdd that I want to connect to the Raspberry pi3 without the need to pay for a powered usb hub to run it through, this is to reduce cost, and to reduce footprint.

My idea was to desolder the usb votlage input socket on the Pi, and change it for a barrell conector that is a bit more robust, then have a 5v power brick which connects to the barrell, which is soldered to the Pi.

Then the plan (which i dont know is a good one or not) is to jump some wires over to the usb external hdd from the barrell conenctor,

This in theory will give me a direct power link from the power brick to the usb hdd, but what I dont know is if injecting 5v into the output side of a usb port will bugger it up?

Could I cut the 5v rail of the usb port and avoid that potential problem?

If anyone has any experience or ideas im all ears!

Ta in advance.

#2

And as sods law would have it, google threw this up, which I coudlnt find before posting. http://rdlazaro.info/compu-Raspberry_Pi-no_power_feeding.html

So from the looks of this he is connecting just USB data and GND to the rasp pi. Then the hub is powering things.

I think that, and my idea above shoudl work out the same?

#3

First, is your external hdd 3.5" or 2.5"? If it is 3.5", it is likely to require 12v, then it splitting the power to your PI won't be possible. Otherwise I don't see why not. You might not even need to desolder/solder if you don't want to. You can just buy a "micro usb to 2.1mm" converter, so you can plug your barrel connector directly into that, and converter into the micro usb input on the PI.

Then to split the barrel connector into 2 outputs, you can consider buying a"2.1mm splitter". Both can be found on eBay.

#4

it is 2.5mm and normally powered just via USB, it is just that the Pi has a rather low amperage rating on its usb ports, something like 140ma is what I remember reading.

I am going to be desoldering all of the usb ports, power port and RJ45 port from the Pi anyway in order to reposition them in the 3d printed case and make it all fit nicely.

So I think I will put two USB ports at the front of the case, one at the back and keep one internal which will have the additional power running to it. Infact, I may also power the rear usb port from the barrel connector just incase I need more power on an external port further down the road.

I just seems a lot more cost effective to buy a 5v 4a power supply and run the show from that than to buy a powered usb hub.

#5

Have you seen THIS btw ?? https://www.hackster.io/idreams/boost-usb-current-in-raspberry-pi-a1531d

;)

also you should really avoid the USB hub which you mentioned. aka "Mac murderer" https://www.youtube.com/watch?v=Uh6iKilgtG0

;)

#6

That first link is interesting. But im not sure i would like to overdrive anything on the pi itself, I will look into it though.

Also the second video highlights exactly the problem I was asking about. its good to know that I caught this potential blunder before I did it.

#7

spruce_m00se: That first link is interesting. But im not sure i would like to overdrive anything on the pi itself, I will look into it though.

Also the second video highlights exactly the problem I was asking about. its good to know that I caught this potential blunder before I did it.

The pi (model B+ and up) can safely give 1.2 amp out through its USB ports (total, just make sure your power supply is capable of 3 amps or the pi won't get enough power and restart.

A typical 2,5 inch HDD uses only about 3W, 600mA max.

Alternatively you can simply use a USB Y cable to power the hard drive directly from the wall wart. Better than a powered USB hub in my opinion, most external 2.5" hdd enclosures use this setup.

#8

Noobian: The pi (model B+ and up) can safely give 1.2 amp out through its USB ports (total, just make sure your power supply is capable of 3 amps or the pi won't get enough power and restart.

A typical 2,5 inch HDD uses only about 3W, 600mA max.

Alternatively you can simply use a USB Y cable to power the hard drive directly from the wall wart. Better than a powered USB hub in my opinion, most external 2.5" hdd enclosures use this setup.

surely a usb y cable risks backfeeding the UAB on the PI as it would essentially be the same as a bad powered hub. Unless of course one side of the Y only has data lines and ground.

I think I will just jumper some wires from the main power in, to my device, and cut the power line on the USB from the PI, the worst that can happen is that it wont work, lol

#9