scottk
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Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 3:38 pm

Hello,
I tried powering a USB hard drive with a dual USB cable (sometimes called a Y-cable). I'm using this drive as a USB boot drive. With both the data and power USB ends plugged into the Raspberry Pi 3 itself, I'm unable to boot. The red lights blinks, and I think I'm drawing too much current.

I'm powering the Raspberry Pi 3 from a USB power adapter that has multiple USB plugs. it's like a 25W supply, so I know it can power both the Pi and the hard drive. So, I tried plugging the aux power USB end of the Y-cable into the USB power adapter itself. Now, I'm unsure if the Pi is being exposed to two separate 5V supplies - one from the Pi's internal reference and one from the USB hub itself? Is this safe to do? It seems to work.

I drew a picture to better explain.
Safe, but doesn't work
Image

May not be safe, but works.
Image

I'm aware that I can use a different hard drive that's powered with its own adapter, but I'm trying to make use of what I have laying around.

broe23
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 5:22 pm

Get a powered USB hub. The one that I use is Orico that I have. You can also get the APC UPS with USB ports also. The Pi would use one USB port and the Pocket drive would draw power out of the other port. Get a USB power switch for the Pi, so that if you have to shut it down, you just push the button on that jumper cord.
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drgeoff
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 5:57 pm

scottk wrote:
Fri Oct 27, 2017 3:38 pm
May not be safe, but works.
Image
I reckon that is safe. I would have reservations if the RPi and the power leg of the Y-cable were plugged into separate PSUs.

broe23
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 7:47 pm

drgeoff, the only problem is that the Y would also feed power into the USB port for the Pi. One power for each device and a USB cord from the drive to the Pi USB port is how it would be done.
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good.

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rpdom
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 8:07 pm

broe23 wrote:
Fri Oct 27, 2017 7:47 pm
drgeoff, the only problem is that the Y would also feed power into the USB port for the Pi. One power for each device and a USB cord from the drive to the Pi USB port is how it would be done.
Is that a problem? No, not really.

broe23
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 9:37 pm

rpdom wrote:
Fri Oct 27, 2017 8:07 pm
broe23 wrote:
Fri Oct 27, 2017 7:47 pm
drgeoff, the only problem is that the Y would also feed power into the USB port for the Pi. One power for each device and a USB cord from the drive to the Pi USB port is how it would be done.
Is that a problem? No, not really.
Yes the Y cable is a problem, due to it is going to feed power into the USB port from the drive to the Pi. Always use a single USB to Micro from drive to Pi, or just go with one of the mSATA adapters on top of the Pi and get away from another external component and potential problem that can fry the Pi if there is a surge or short between the Pi and external drive.
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good.

sora03
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Re: Powering a 2.5" USB hard drive on Pi3

Fri Oct 27, 2017 11:18 pm

im powering a usb hdd from a pi 2b it is connected to pi 2 usb port (y cable). it os powered by a MP1584 dc dc buck boost con ected from a laptop charger, always make sure that the microusb cable is thick and not cheap since it is always the cause of pi being throttled. i also have a cheap usb hub but whenever i connect it the drive mysterioualy disconnects if theres a high hdd activity
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HawaiianPi
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 12:38 am

sora03 wrote:
Fri Oct 27, 2017 11:18 pm
im powering a usb hdd from a pi 2b it is connected to pi 2 usb port (y cable).
Using a Y-cable on the Pi2 USB ports is pointless, because the Pi2 does not have any per-port power limits. A Pi2 can output up to 1.2A from its USB ports, and all of that can go to one port if there is nothing else in the other ports (or only low power peripherals). Note that on the PiB+ and Pi2 you need to add max_usb_current=1 to config.txt to get the 1.2A output (default on the Pi3).
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scottk
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 2:07 am

broe23 wrote:
Fri Oct 27, 2017 7:47 pm
drgeoff, the only problem is that the Y would also feed power into the USB port for the Pi. One power for each device and a USB cord from the drive to the Pi USB port is how it would be done.
The interesting (scary) thing is, if I power the hard drive first, nothing happens on the PI (it stays powered off). Once I plug the Pi's power cable in, things power up. And then when I shut down, IF I unplug the Pi power but leave the HDD plugged in, the Pi stays powered up (red LED lit).

I don't really understand how the Pi is powered. Does the 5V from the supply go through some kind of regulator to get to the 5V on the four onboard USB ports?

broe23
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 2:22 am

I have actually had the Pi 2 and 3 that I have, power up to where there is enough voltage to cause the LED's to light up. This has been with every adapter that I use, so I tend to warn people, since there have been posts from others that they had the same backfeed issue. I do the setup as I described, so that there is no issues.

I would get away from the external and extra power, just go with the mSATA adapter that is out there and then you do not have to worry about the possibility of any back feed issues.
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good.

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rpdom
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 7:58 am

scottk wrote:
Sat Oct 28, 2017 2:07 am
The interesting (scary) thing is, if I power the hard drive first, nothing happens on the PI (it stays powered off). Once I plug the Pi's power cable in, things power up. And then when I shut down, IF I unplug the Pi power but leave the HDD plugged in, the Pi stays powered up (red LED lit).

I don't really understand how the Pi is powered. Does the 5V from the supply go through some kind of regulator to get to the 5V on the four onboard USB ports?
The power to the USB ports is switched by the USB controller chip. Initially the power is turned off, but is enabled during the boot sequence. Once enabled, power can flow in both directions, in or out of the USB ports. So that is why your Pi stays power from the USB ports after startup, but won't start if powered from cold on the ports.

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rpdom
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 8:00 am

HawaiianPi wrote:
Sat Oct 28, 2017 12:38 am
Using a Y-cable on the Pi2 USB ports is pointless, because the Pi2 does not have any per-port power limits. A Pi2 can output up to 1.2A from its USB ports, and all of that can go to one port if there is nothing else in the other ports (or only low power peripherals). Note that on the PiB+ and Pi2 you need to add max_usb_current=1 to config.txt to get the 1.2A output (default on the Pi3).
I believe there has been a change in recent firmware so that option isn't needed on the B+ or Pi2B either now.

I haven't tested it yet.

drgeoff
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 10:40 am

HawaiianPi wrote:
Sat Oct 28, 2017 12:38 am
sora03 wrote:
Fri Oct 27, 2017 11:18 pm
im powering a usb hdd from a pi 2b it is connected to pi 2 usb port (y cable).
Using a Y-cable on the Pi2 USB ports is pointless,
'It is not always pointless. https://github.com/raspberrypi/firmware/issues/842

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rpdom
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Oct 28, 2017 10:54 am

drgeoff wrote:
Sat Oct 28, 2017 10:40 am
HawaiianPi wrote:
Sat Oct 28, 2017 12:38 am
sora03 wrote:
Fri Oct 27, 2017 11:18 pm
im powering a usb hdd from a pi 2b it is connected to pi 2 usb port (y cable).
Using a Y-cable on the Pi2 USB ports is pointless,
'It is not always pointless. https://github.com/raspberrypi/firmware/issues/842
I think you did a dougie (misread the post ;-) ). HawaiianPi is talking about using a Y-cable with both USB plugs in sockets in the Pi, not the USB data plug in the Pi and the extra power plug in an external source.

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Re: Powering a 2.5" USB hard drive on Pi3

Sun Oct 29, 2017 5:06 am

rpdom wrote:
Sat Oct 28, 2017 10:54 am
I think you did a dougie (misread the post ;-) ). HawaiianPi is talking about using a Y-cable with both USB plugs in sockets in the Pi, not the USB data plug in the Pi and the extra power plug in an external source.
Yes, I was replying to the post I quoted, not the OP (hence, the quote).
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broe23
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Re: Powering a 2.5" USB hard drive on Pi3

Sun Oct 29, 2017 6:04 am

rpdom wrote:
Sat Oct 28, 2017 7:58 am
scottk wrote:
Sat Oct 28, 2017 2:07 am
The interesting (scary) thing is, if I power the hard drive first, nothing happens on the PI (it stays powered off). Once I plug the Pi's power cable in, things power up. And then when I shut down, IF I unplug the Pi power but leave the HDD plugged in, the Pi stays powered up (red LED lit).

I don't really understand how the Pi is powered. Does the 5V from the supply go through some kind of regulator to get to the 5V on the four onboard USB ports?
The power to the USB ports is switched by the USB controller chip. Initially the power is turned off, but is enabled during the boot sequence. Once enabled, power can flow in both directions, in or out of the USB ports. So that is why your Pi stays power from the USB ports after startup, but won't start if powered from cold on the ports.
With the powered external 2.5" enclosure I have, if you use external power on it and connect the USB output to the PI, along with the Pi not turned on yet, it will actually turn the green LED on, but not boot the Pi. It also did it when I had only the USB on the Orico and the power and USB for the PI, but the pi power not turned on, which also caused the green LED to light. That happens also on the Pi 2 I have. There is something going on in both of those models that the controller is allow a very low current to still leak through.
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sora03
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Re: Powering a 2.5" USB hard drive on Pi3

Mon Oct 30, 2017 2:54 am

it is not pointless to connect a usb hdd to 2 ports of the pi usint a y cable. if i do not connect the other cable to the port the hdd fails and pi wont boot. the config.txt must enabled 1.2A and there should be a delay in mounting the root parrtition /boot/cmdline rootdelay=10
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Re: Powering a 2.5" USB hard drive on Pi3

Mon Oct 30, 2017 10:43 am

sora03 wrote:
Mon Oct 30, 2017 2:54 am
it is not pointless to connect a usb hdd to 2 ports of the pi usint a y cable. if i do not connect the other cable to the port the hdd fails and pi wont boot.
That sounds like a problem with the cable (either the data connector has no power connection, or the power conductors are too thin).
The point is that the Pi design allows a USB device to be connected to a single USB port and draw up to 1.2A ( actually the total for all USB devices), as long as the USB cable is capable of carrying that current without too much voltage drop.
Have you tried a standard USB cable with thick enough wires? Shorter cables also help.
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sora03
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Re: Powering a 2.5" USB hard drive on Pi3

Mon Oct 30, 2017 2:16 pm

davidcoton wrote:
Mon Oct 30, 2017 10:43 am
sora03 wrote:
Mon Oct 30, 2017 2:54 am
it is not pointless to connect a usb hdd to 2 ports of the pi usint a y cable. if i do not connect the other cable to the port the hdd fails and pi wont boot.
That sounds like a problem with the cable (either the data connector has no power connection, or the power conductors are too thin).
The point is that the Pi design allows a USB device to be connected to a single USB port and draw up to 1.2A ( actually the total for all USB devices), as long as the USB cable is capable of carrying that current without too much voltage drop.
Have you tried a standard USB cable with thick enough wires? Shorter cables also help.
the only cable that i can try is the Usb cable from an external USB DVD-RW that about 0.5 in long, written on the cable 24AWG/2c + 28 AWG/2c it appears to be thick.
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Re: Powering a 2.5" USB hard drive on Pi3

Mon Oct 30, 2017 2:35 pm

sora03 wrote:
Mon Oct 30, 2017 2:16 pm
davidcoton wrote:
Mon Oct 30, 2017 10:43 am
Have you tried a standard USB cable with thick enough wires? Shorter cables also help.
the only cable that i can try is the Usb cable from an external USB DVD-RW that about 0.5 in long, written on the cable 24AWG/2c + 28 AWG/2c it appears to be thick.
Worth a try. -- 24AWG should be OK. 22AWG would be better. The official Pi PSU attached cable is 18AWG (thicker!)
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Re: Powering a 2.5" USB hard drive on Pi3

Sat Mar 10, 2018 8:33 am

May I add another problem?
I am using a 1Tb hdd (seagate) which I am powering separately. The usb plug is 3.0.

Plugged into the usb ports are the hdd, keyboard and mouse. Up to that point all works well. However when I need to add two other usb devices through a 4 port usb hub (an interface to my ham radio and the radio CAT control) the keyboard and mouse freezes and I cannot use the computer. Powering the usb hub does not make a difference.
The hdd is powered separately from a 3 amp supply using a Y cable . I detached the 5 volt + line in the rpi usb plug to isolate the power limitation of the Rpi.

To me it appears that the hdd is occupying to much data space in the usb system of the Rpi.

Does anyone have a solution to this problem?

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