PiWipe
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Powering two USB HDDs

Sat Sep 24, 2016 1:15 pm

I have a Pi 3 connected to an approved 2.5A supply and running openmediavault.

I have set max_usb_current=1 in config.txt.

If I connect two Seagate 2TB Backup Plus Slim drives to USB ports one above the other on the Pi the drives start and stop repeatedly, which I take to be a power supply issue.

However if I connect them to side-by-side USB ports they behave properly.

Can anyone explain this behaviour? There are no other USB devices connected to the Pi.

Mike

klricks
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Re: Powering two USB HDDs

Sat Sep 24, 2016 6:58 pm

PiWipe wrote:I have a Pi 3 connected to an approved 2.5A supply and running openmediavault.

I have set max_usb_current=1 in config.txt.

If I connect two Seagate 2TB Backup Plus Slim drives to USB ports one above the other on the Pi the drives start and stop repeatedly, which I take to be a power supply issue.

However if I connect them to side-by-side USB ports they behave properly.

Can anyone explain this behaviour? There are no other USB devices connected to the Pi.

Mike
What are the current ratings of the drives? I would not have expected 2 drives to work at all.
The max_usb setting only applies to B+ and 2B models. The max current setup (1.2A) is default on the 3B.
Do the drive USB connectors touch or interfere with each other when in the same stack?
Do you have the same problem when booting from a cold start vs hot-plugging the drives after boot?
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

PiWipe
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Re: Powering two USB HDDs

Sun Sep 25, 2016 7:13 pm

Thanks for your reply and explaining about the max current setting. I have googled in vain and cannot find a current rating for these drives.

The problem occurs either when booting the Pi or hot plugging the drives. One is fine but two cause the problem. It's obviously an overcurrent issue and I have now fixed it by running the drives from a powered hub, but it's a bit annoying having to run two wall warts for an always-on NAS.

Mike

mosespi
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Re: Powering two USB HDDs

Sun Sep 25, 2016 7:36 pm

PiWipe wrote:I have a Pi 3 connected to an approved 2.5A supply and running openmediavault.

I have set max_usb_current=1 in config.txt.

If I connect two Seagate 2TB Backup Plus Slim drives to USB ports one above the other on the Pi the drives start and stop repeatedly, which I take to be a power supply issue.

However if I connect them to side-by-side USB ports they behave properly.

Can anyone explain this behaviour? There are no other USB devices connected to the Pi.

Mike
I'll take a guess.. top to bottom they are on the same 'physical' USB port 'pair' and they likely share a common PCB power trace going to them. Plugging them in side by side gives you a different trace. Now they all share the same 5v power bus obviously, but plugging two into the same port that share a particular trace on the PCB may give you enough of a voltage drop with two drives trying to power up that this causes your problem.

This does tell us the drives are right on the edge of working, so even plugged in side by side a small change (temperature, cosmic rays, etc..) may cause them to fail too.

You are limited by normal USB to a certain power range (until USB C, or something else becomes commonly available for the Pi), so that is what we have to deal with. If you want just one 'wire' going to your NAS, you can always take in a higher voltage DC source, say 12 volts, into your NAS 'box' and then split that up using DC converters for the 5v to run your Pi and drives. Or get a super high power 5v wall wart that is not USB and convert it to USB plugs inside your NAS box. Or maybe a high power hub will do.

Regards,
-Moses
Power problems? MoPower UPS for the Pi
http://www.allspectrum.com/mopower/

PiWipe
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Re: Powering two USB HDDs

Mon Sep 26, 2016 11:24 am

Hi Moses

Thanks for your reply. I may not have been clear in my post, but the Pi IS the NAS :D . That's why I need it to run the two HDDs.

As it will be always on I would like to keep power consumption to a minimum. I thought that the Pi's 2.5A supply would be sufficient to power it and the HDDs but I guess what you're saying is that voltage drops on the Pi's PCB are preventing the drives from starting up.

Mike

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pi-anazazi
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Re: Powering two USB HDDs

Mon Sep 26, 2016 11:43 am

Hi!

I have some pi-NAS with 2x 3.5'' HDDs, usually I use something like this her:

https://www.amazon.com/UNIWENT-SATA-5-2 ... B000YJBL78

and get the power for the HDDs (and raspi) from some external power supply. Whatever gives you rock-solid 5v/12v... ;-)
Kind regards

anazazi

klricks
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Re: Powering two USB HDDs

Mon Sep 26, 2016 1:12 pm

PiWipe wrote:Hi Moses

Thanks for your reply. I may not have been clear in my post, but the Pi IS the NAS :D . That's why I need it to run the two HDDs.
??? there is no requirement that a NAS have 2 drives. Most have only one.

PiWipe wrote:As it will be always on I would like to keep power consumption to a minimum. I thought that the Pi's 2.5A supply would be sufficient to power it and the HDDs but I guess what you're saying is that voltage drops on the Pi's PCB are preventing the drives from starting up.

Mike
As mentioned the USB ports on the RPi can only supply 1.2A combined total of all 4 ports.
Here is a chart of power consumption of various drives: http://www.tomshardware.com/reviews/2tb ... 630-9.html
The chart is in Watts so to convert to Amps you need to use W/V=A.
So for 2 drives to run on a RPi they can be no more than 3W (0.6A) each. Or 6W (1.2A) for a single drive. (This does not include the power consumed by the USB to SATA converter).
The power consumption would be on a sticker on the NAS box or on the 'raw' drives.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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Burngate
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Re: Powering two USB HDDs

Mon Sep 26, 2016 3:32 pm

PiWipe wrote:... It's obviously an overcurrent issue and I have now fixed it by running the drives from a powered hub, but it's a bit annoying having to run two wall warts for an always-on NAS.
If the hub has more than two outputs, and its supply is man-enough, can you not power the Pi from a third hub output?

mosespi
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Re: Powering two USB HDDs

Mon Sep 26, 2016 5:04 pm

PiWipe wrote:Hi Moses

Thanks for your reply. I may not have been clear in my post, but the Pi IS the NAS :D . That's why I need it to run the two HDDs.

As it will be always on I would like to keep power consumption to a minimum. I thought that the Pi's 2.5A supply would be sufficient to power it and the HDDs but I guess what you're saying is that voltage drops on the Pi's PCB are preventing the drives from starting up.

Mike
Adding another supply will just add its minimum idle current to the mix.. maybe 1 watt or so, depending on the supply. It won't even really be idling, so I'm not even sure it would make any noticeable increase. Nothing to worry about I would say. The efficiency level of your power supply and particular hard drive consumption will likely make the biggest difference.

I'll second the powering of everything from one super power hub if you really like a single power input, probably the least hassle solution.

Regards,
-Moses
Power problems? MoPower UPS for the Pi
http://www.allspectrum.com/mopower/

PiWipe
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Re: Powering two USB HDDs

Tue Sep 27, 2016 10:29 am

Thanks for the ideas. In response:

I have two drives so I can mirror the data.

There is nothing on the drive labels to indicate power consumption, and Google has failed me there.

My USB hub has plenty of spare sockets and a 2.0 amp supply so I will see if that will power the drives and the Pi.

Mike

peterlite
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Re: Powering two USB HDDs

Tue Sep 27, 2016 12:04 pm

USB 3 hubs supply more power per port. Some USB 3 hubs have 4 amp power supplies. I run a Pi 3 and some disks from a WS-UH3074 USB 3 hub with its 4 amp power supply. The hub plugs into the Pi 3 and one port supplies power to the Pi. My disks run at just under an amp, which means I could run three disks.

PiWipe
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Re: Powering two USB HDDs

Tue Sep 27, 2016 12:25 pm

I've had another idea. I've got a mains extension lead which contains 2 x 2.4A USB charging sockets.

I could use one socket to power the Pi and try backfeeding the hub with the other to supply the HDDs.

It might consume less power than two separate wall warts.

Mike

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pi-anazazi
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Re: Powering two USB HDDs

Tue Sep 27, 2016 12:28 pm

...USB3 hubs? Had a look and found this here:

http://downloads.cdn.re-in.de/1200000-1 ... EPORTS.pdf

Sounds interesting!
Kind regards

anazazi

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davidcoton
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Re: Powering two USB HDDs

Tue Sep 27, 2016 3:56 pm

PiWipe wrote:It might consume less power than two separate wall warts.
Why? A socket with USB power outlets is only like building the wall warts into the wall :lol:
Location: 345th cell on the right of the 210th row of L2 cache

PiWipe
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Re: Powering two USB HDDs

Wed Sep 28, 2016 11:54 am

davidcoton wrote:
PiWipe wrote:It might consume less power than two separate wall warts.
Why? A socket with USB power outlets is only like building the wall warts into the wall :lol:
Except that one built-in supply might consume less power than two external ones. I will measure them.

I had a less than helpful reply from Seagate "Technical Support" about my drives' current consumption. I asked for peak and mean currents and they replied "500mA USB".

Mike

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