Raspberry Pi hard drive

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Re: Raspberry Pi hard drive

Postby johnbanks » 19 Mar 2016, 11:12

PeteB ...
Completely agree with you on low impedance USB charging cables.
I make my own using cheap speaker wire (only 2 wires are needed)
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Re: Raspberry Pi hard drive

Postby PeteB » 19 Mar 2016, 15:07

Completely agree with you on low impedance USB charging cables.
I make my own using cheap speaker wire (only 2 wires are needed)

Hi John!

(I've been reading your WiFi posts, hoping you you or someone else will solve that for me... :D)

If you can make your own cables, that is obviously ideal. There are some better cables on amazon made by Anker and IXCC, with lower impedance power wires (20 and 22 AWG), but still nothing compared to a typical supply in any audio gear.

With the typical charger-type power supply and wiring, by the time you add hard drive storage, and/or attach an ethernet cable, the advertised SNR of the dac is pretty much history.

HiFiBerry has a provision to add a separate power supply to their DAC+ Pro, but not to the DAC+ which I own. They also warn against hardwired ethernet if you want the best possible performance.
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Re: Raspberry Pi hard drive

Postby Grundgütiger » 19 Mar 2016, 22:41

PeteB wrote:In the meantime, using a short and low impedance USB charging cable, the kind where they publish the wire gauge like some of the IXCC cables on Amazon, will actually help our application more than a 2.5A supply... :D
Cheers,
P.


johnbanks wrote:PeteB ...
Completely agree with you on low impedance USB charging cables.
I make my own using cheap speaker wire (only 2 wires are needed)


Good ideas. I sometimes thought about changing something on this charging side, but never got the "pressure" doing so. I guess, I'll start tonight. :D

Edit:
This reminds me of the Kraftwerk song "Ohm Sweet Ohm" :lol:
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Re: Raspberry Pi hard drive

Postby PeteB » 20 Mar 2016, 04:25

I did some quick measurements using an inline USB power/multi-meter, using a WD5000LPVX as an example, but first this...

From StorageReview.com, measurements of a WD5000LPVT, the interesting part is at the end of the article, a bar graph showing power under various conditions.

wd_scorpio_blue_500gb_power_values.png
wd_scorpio_blue_500gb_power_values.png (22.36 KiB) Viewed 1431 times

Full article:
http://www.storagereview.com/western_digital_scorpio_blue_review_500gb_7mm_wd5000lpvt

Now, my own measurements (accuracy should be +/- 0.02A or better):

Idle 0.20A, ~1.0W
Read/Write 0.52A, ~2.6W
Startup 0.88A, ~4.4W (significantly more than LPVT version!)

The last reading is the only really bad news. A relatively low-power 7-mm hard drive with a single platter is using 3/4 of the current allowance for all four USB combined.

That probably explains why some typical laptop drives work when powered only from a single RPi USB port, even though it technically exceeds the Raspberry Pi official current allowance by a wide margin, and therefore, not recommended.

Also, when the drive uses the maximum observed current during its startup, the voltage at the USB port drops to about 4.65 V for a short time, which is below the USB spec. This might interfere with the startup of other USB-powered devices such as a WiFi dongle. In other words, it causes a momentary brownout on power up.

With a better power supply (read, NOT a wall-wart), a good cable, and some capacitors for around $2 maybe, I bet the brownout would not happen.

P. (Ohm, ohm on the range.... oh, never mind, :mrgreen: )
Last edited by PeteB on 20 Mar 2016, 15:43, edited 1 time in total.
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Re: Raspberry Pi hard drive

Postby Grundgütiger » 20 Mar 2016, 10:23

I found an article that also explains some of the writings on USB cables for identifying the vein's thickness. Also read the comments. (The cable I'm using to connect the HDD to the Raspberry Pi is very short and quite thick, so I guess the inner values are ok. It doesn't have any of the mentioned writings.)

http://goughlui.com/2014/10/01/usb-cable-resistance-why-your-phonetablet-might-be-charging-slow/
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Re: Raspberry Pi hard drive

Postby ACX » 20 Mar 2016, 11:14

Grundgütiger wrote:Edit:
This reminds me of the Kraftwerk song "Ohm Sweet Ohm" :lol:

I love it! :)
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Re: Raspberry Pi hard drive

Postby PeteB » 20 Mar 2016, 15:35

That is a good article. The est part IMO is the section that explains the relationship between the gauge of the wire (the awg number), the resistance per foot, and resulting voltage drop.

You can easily see why adding between 0.5 and 1A of intermittent current demand to the USB ports of a Raspberry Pi is a problem.

In addition to playing havoc with the other USB devices, the "intermittent" part translates to extra noise on the ground and the 5V supply, and lowers the signal-tonoise ratio. No wonder the HiFiBerry team has an option to add a separate supply to at least one of their DAC boards.

Fortunately, 20 awg cables are easy to find on amazon, ebay, etc., if you know what to look for.
ANKER_613kRlSuYKL._SL1000_.jpg
Diagram of the wires of the Anker cable with wire gauge labeled
ANKER_613kRlSuYKL._SL1000_.jpg (59.3 KiB) Viewed 1433 times

The brownout situation can also be remedied partially by selecting a supply with a higher nominal output voltage. Gizmo Junkies sells one rated at 5.3V (gizmojunkies.com, and amazon.com).
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Re: Raspberry Pi hard drive

Postby johnbanks » 20 Mar 2016, 18:30

I've purchased several of these ...

http://www.modmypi.com/raspberry-pi/accessories/power-supplies/5v-2a-ultra-hq-usb-power-supply-uk

I make up a 2 wire power cable using speaker wire with a male USB at each end and then connect to the RPi via a short (2 or 3 inches) USB female to micro male adaptor cable. Has the advantage that the USB male to female interface can be the power 'switch' which avoids straining the micro socket on the RPi.
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Re: Raspberry Pi hard drive

Postby PeteB » 24 Mar 2016, 05:45

Grundgütiger wrote:I use just an average external 2,5" 1TB hard drive, USB powered. If you change the config.txt file of the Linux system the Raspberry Pi is able to power the hard drive - if your Raspberry's power supply is strong enough. But maybe the PiDrive somehow has some Raspberry Pi goodies.


After some research, it looks like the standard USB drive is the way to go...

I've done some reading, and the WD 314 drive is pretty severely crippled. Not only the capacity, but the platter transfer rate, the USB data rate, etc, etc...

This will not work for me. I want to be able to take the entire audio player and plug into it from a PC USB port, and edit tags, transfer files, check the SMART parameters now and then, etc.

I have tested three older conventional 2.5" drives from my parts bin, using an SATA adapter, and one new-ish native USB drive (the WD Passport 1 TB Ultra). 3 out of 4 work fine powered from my Pi 2 through a plain USB cable, with normal care about the power supply, short cable, etc. (testing with a WiFi adapter and a WD keyboard wireless dongle, and my DAC+ from HiFiBerry). The only drive that caused the Pi 2 to brown out was an older 3-platter WD Scorpio Black 750gb drive.

So far, it is a close tie between the single-platter WD5000LPVX with USB adapter, and the two platter WD Passport native USB. I would opt for the full 1 TB drive, but the WD5000LPVX seems more within my Pi budget for now.
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Re: Raspberry Pi hard drive

Postby Grundgütiger » 24 Mar 2016, 20:58

I'm still waiting for an answer from the "WDLabsAssistants". I asked for more technical details. If there isn't any technical advantage about using the PiDrive with a Raspberry Pi, I guess it's just another marketing thing. If the enclosure they are selling wasn't so ugly I might have just bought the 1TB drive for that reason. But as long as my set-up works, there's no need for a change.
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