cerebro
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B+ External Hard Drives

Sun Jul 20, 2014 7:12 pm

Hi,

Can anyone recommend a power supply for the new B+ model that will power the Pi and two 2.5 external hard drives?

I have used a 5v 2a power supply and it does not give enough juice to power the drives.
I have not changed any of the power settings on the pi, so if anyone can recommend a supply or a setting to try that would be great.

Thanks In advance.

fruitoftheloom
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Re: B+ External Hard Drives

Sun Jul 20, 2014 7:19 pm

The information is out there....you just have to let it in.

My other Linux machine is a ChromeBox

drgeoff
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Re: B+ External Hard Drives

Sun Jul 20, 2014 7:20 pm

In addition to the info linked to by fruitoftheloom, although the B+ has an uprated polyfuse compared to A/B models it still limits the total current into the board to about 2 amps. A supply giving more than that isn't going to help if the drives are not getting enough power via the USB sockets. If you want to use one PSU, you need to think about the "old hacks" from B days of diverting drive power around the RPi.
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FLYFISH TECHNOLOGIES
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Re: B+ External Hard Drives

Sun Jul 20, 2014 7:23 pm

Hi,
cerebro wrote:Can anyone recommend a power supply for the new B+ model that will power the Pi and two 2.5 external hard drives?
It always helps when the power requirements of the loads (hard drives) are known...
cerebro wrote:if anyone can recommend a supply or a setting to try that would be great.
Google said that by default you can sink 600mA from USB and you can increase that current up to 1.2A with one software setting (google can tell you exactly what to change).

If your disks are USB 2.0 compliant then 1.2A is enough for them... add to this number also RasPi's current consumption and you get a number slightly below 2A.


Best wishes, Ivan Zilic.
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cerebro
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Re: B+ External Hard Drives

Mon Jul 21, 2014 7:07 pm

Hi,

Thanks for all the replies, I have tried the software changes and unfortunately they don’t work for me. I have to USB3.0 hard drives, so I am going back to my old set up of a PiHub powering the pi and the two hard drives, as I know it works.
I will keep an eye out for any power changes published to the model B+ but for now keeping it simple and staying with what works.

Thanks again

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rew
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Re: B+ External Hard Drives

Mon Jul 21, 2014 7:39 pm

I now have a "decent" setup that can measure the output capabilties of various powersources.

Interesting to measure powersupplies marketed as "2A" and then finding out that they max out at 0.35A (just like most 0.5A supplies...)! Anyway, the best powersupply so far is one advertized as 2A which manages just over 1.5A.

My rule-of-thumb is that a 2.5" harddisk draws 1A, so with two drives, you're pushing the limit of the 2A supply even if the pi was infinitely efficient (0 power usage). But then they might draw more than one amp during startup....

So, to get your setup working....
- Can the powersupply manage the two disks + pi? Is it really 2A?
- Does the polyfuse mess things up? Can you power your pi through the 5V on the GPIO port?
- Can you measure the current draw of your harddisks?
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Re: B+ External Hard Drives

Mon Jul 21, 2014 7:39 pm

The maximum current permitted, 1.2A, is not sufficient to power 2 external USB HDDs. The spin-up surge from either drive, when the other is running will trip the overcurrent detection.

Works fine with all of the drives I've tested singly, though.
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Re: B+ External Hard Drives

Mon Jul 21, 2014 7:50 pm

rew wrote:I now have a "decent" setup that can measure the output capabilties of various powersources.
Interesting to measure powersupplies marketed as "2A" and then finding out that they max out at 0.35A (just like most 0.5A supplies...)! Anyway, the best powersupply so far is one advertized as 2A which manages just over 1.5A.
...
Slightly O.T., but whilst I was waiting for my first Pi, back in 2012, I began an investigation of the performance of various potential PSU's for said Pi (and/or a powered hub) - you may be interested in those results and other, later, measurements:
http://www.cpmspectrepi.webspace.virgin ... plies.html
http://www.cpmspectrepi.webspace.virgin ... dPSUs.html
Trev.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, 2xB2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, and a A+) but Buster on the P4B's & P400. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

chorlton2080
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Re: B+ External Hard Drives

Fri Aug 01, 2014 10:20 am

Something else to consider. Do you not need to do the following to enable maximum power to the B+ USB?

Code: Select all

sudo nano /boot/config.txt
.....
safe_mode_gpio=4

phelum
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Re: B+ External Hard Drives

Fri Aug 01, 2014 10:57 am

chorlton2080 wrote:Something else to consider. Do you not need to do the following to enable maximum power to the B+ USB?

Code: Select all

sudo nano /boot/config.txt
.....
safe_mode_gpio=4
With this USB power upgrade (1200ma across all 4 ports) I can run one HDD and a keyboard and mouse. But that is about all. Running multiple drives needs an external power supply. With 1200ma for USB devices and 600ma for the RPi B+ the total is 1.8A which is the limit for the power connector. And the power cable needs larger wires than most USB cables to supply the current without a prohibitive voltage drop.

Cheers,
Steven

chorlton2080
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Re: B+ External Hard Drives

Sat Aug 02, 2014 2:11 pm

Regarding the USB cable annoyance: PortaPow 'fast charging' cables are proven to provide just over 2A. I can't get enough of them!

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