ladius
Posts: 14
Joined: Sun Mar 15, 2015 4:18 pm

Pi 3 not powering disks

Mon Nov 20, 2017 5:34 pm

I'm attempting to recover some files with Photorec from a USB hard drive (to another), and since I didn't want to leave my laptop on just for this, I plugged it in to my Pi 3.

I have the official Raspberry power adapter (2A), a Pi 3 and a 2'5 hard drive from an old laptop. Plugged it in, booted the Pi and plugged in the other 2'5 hard drive and the Pi couldn't power both, they kept going on and off. Tried with the "max_usb_current=1" setting, same thing.

Thinking it would consume less power, I un-dusted my old Pi 1 B, connected to the same PSU, and the disks are powered fine here. However the thing here is that Pi 1 B actually seems to be more power hungry than the Pi 3 (source: http://raspi.tv/2016/how-much-power-doe ... ed-to-pi2b)

So my question is, am I doing something wrong? Is my Pi 3 somehow broken? (it isn't even half a year old and didn't even went through heavy usage like my Pi 1 did).

Between the two Pi's, the PSU and SD card were the same. Both always connected to ethernet.

pcmanbob
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Location: Mansfield UK

Re: Pi 3 not powering disks

Mon Nov 20, 2017 7:59 pm

You are unlikely to be able to power 2 x 2.5"HD directly from your pi as you only have 1.2A max shared across all the USB ports.

To run 2 drives you will need a good powered USB hub capable of supply the required power for the 2 x 2.5"HD
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ladius
Posts: 14
Joined: Sun Mar 15, 2015 4:18 pm

Re: Pi 3 not powering disks

Wed Nov 22, 2017 6:53 pm

pcmanbob wrote:
Mon Nov 20, 2017 7:59 pm
You are unlikely to be able to power 2 x 2.5"HD directly from your pi as you only have 1.2A max shared across all the USB ports.

To run 2 drives you will need a good powered USB hub capable of supply the required power for the 2 x 2.5"HD
My question isn't if they can be powered. As stated in my post, they can. However, I do not understand why a Pi 1 B can power both disks, but a Pi 3 no. Any clues on this?

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rpdom
Posts: 17174
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Pi 3 not powering disks

Wed Nov 22, 2017 7:05 pm

The Pi 3B has power monitoring and limiting on the USB ports. The Pi 1B does not. (except the early versions with the 140mA polyfuses on each port).

However, the Pi 1B has a much lower value polyfuse on the micro USB power input. 700mA iirc, which means 700ma for the Pi and USB ports combined, which isn't enough for even one USB powered drive. The only way you could do that is to bypass the fuse, either by shorting it out, or by powering via the GPIO pins.

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