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I was not able to power an external HD directly from a Raspberry pi 3 (the HD was constantly complaining about a lack of power). Would a Raspberry Pi 4 be able to power a portable hard drive (using the standard charger)?

tlfong01
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raspberry
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  • What type of HD? A 2.5" hard drive, a SSD, a 3.5" drive? – Fred Sep 20 '19 at 22:20
  • I have no trouble powering a 2.5" HDD on the pi 4 if that helps – Jaromanda X Sep 21 '19 at 04:34
  • I have checked that Seagate 2TB takes about 400mA. So if you are using 5V 3A for Rpi4, you more or less make it. But I would recommend to use SSD, whose price is falling rapidly: https://raspberrypi.stackexchange.com/questions/103784/can-a-raspberry-pi-4-power-an-external-hd – tlfong01 Sep 27 '19 at 13:49
  • One HDD is typically fine but there will be not much power left for the remaining USB ports – Dmitry Grigoryev May 03 '20 at 02:36

5 Answers5

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not able to power ... from a Raspberry pi 3

Here's why: Pi 3 was designed with USB 2.0 specs, including the 0.5 amp limit. Most hard drives require more current than that.

Raspberry Pi 4 has USB 3.0, which means it is designed to supply up to 1 amp. That is likely enough to run the hard drive.

Botspot
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5

Answer

hdd/ssd power requirements If your Rpi4B's power supply meets the official spec of 3A output, then it is OK to use USB HDS/SSD without external power supplies.

I measured the idle current and write current of a 1TB SSD, and a2TB HDD.

SSD's idle current is 0mA, and write current around 180mA

HDD's idle (spinning) current is 170mA, and write current 200mA ~ 380mA

My conclusion is that for hobbyist's python programming projects with casual use of SSD or HDD, there is no need to supply external power to the USB hub.

If two SSDs are used for professional projects, it is better to supply external power to the USB hub.

References

(1) USB HDD/SSD Power Requirements

tlfong01
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    I suggest you include the initial spin-up current, as that would seem to be the highest. – Botspot Sep 22 '19 at 12:23
  • @Botspot, Good idea, let me search my junk posts. – tlfong01 Sep 22 '19 at 13:02
  • @Botspot, Just now I searched my old posts on a couple of forums I have been hopping around, and found that I usually started discussions with a colourful picture, and I think I shall use this picture to start another discussion: https://penzu.com/public/a25b1076. I need to stare at this picture for 3 minutes, to refresh my memory! :) – tlfong01 Sep 22 '19 at 13:18
  • @Botspot, The picture above reminds me that the voltage/current/speed characteristic is a multidimension thing, beside non linear. From the chart, I think I can only guesstimate that the max current is the stall current, which should be at most two or three times of the steady current. But now I am looking at another diagram: https://www.raspberrypi.org/forums/viewtopic.php?f=91&t=232753&p=1433763&hilit=motor+current#p1435033. Again I need to stare at it for 3 minutes, to refresh my memory. – tlfong01 Sep 22 '19 at 13:31
  • @Botspot, I guess the HDD motor needs perhaps a couple of minutes (not sure) to arrive at the steady state, when the read/write heard slides on a very thin air layer, blah, blah, blah, .. Since the motor coil is an inductor, so the current starts at very small and goes up exponentially (opposite of a capacitor which the initial current is "infinite". In other words, the initial spinning current is smaller than the steady current, so no need to bother. I also read that modern HDD using BLDC motor, which I have played only for a short while, so cannot make any even quick and dirty comments! :( – tlfong01 Sep 22 '19 at 13:40
  • @Botspot, On second thought, I do remember often reading that a motor starts with "a rush current", ... I don't understand why. Perhaps I made some mistake somewhere. Comments welcome! :) – tlfong01 Sep 22 '19 at 14:02
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    Yes, when a motor is initially spinning up, it takes more current than when it is coasting at full speed. (This is because it has to combat inertia + friction instead of only friction). – Botspot Sep 22 '19 at 18:59
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    That's why large drill press machines have a two-stage startup switch: the first setting on the switch limits the current. Once the motor reaches full speed, the operator clicks the switch again. If they didn't have this feature, the drill presses would likely trip a breaker! – Botspot Sep 22 '19 at 19:01
  • @Botspot, Ah, so it is the intertia + friction that makes the motor start very slow, so slows that the current is as large as it is stalled. In large drill press machines, the start or stall current might be 100A or more. But for HDD, I think the power circuit is smart to use over current limiting so there might not be any rush current at all. BTW I also read that the HDD power circuit is very smart, with a built in accelerometer, so if there is a free fall or shock, the protection immediately kick in and cut power or something, ... – tlfong01 Sep 27 '19 at 13:59
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I have a spare nintendo switch charger (15V 2.6amp) that I am using and I am trying to copy my system to a mechanical Seagate Backup Plus (4TB). The drive mounts fine, and I can copy files of trivial size back and forth; but when I start rsync, my pi shuts down a few seconds later.

My Answer to the question is yes, you can use an HD with the raspberry pi, but if you aren’t using right charger you will likely have problems.

I wanted to post this as a comment, but I apparently don’t have enough reputation for that...

videomonkey43
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Yes, i'm trying to use hard drive on raspberry pi 3b+ , but it's not working .so i bought raspberry pi 4 it's working on it . when i'm trying use HDD on rpi3 answer from google - maybe you can external power supply to deliver power to HDD. all over i didn't found any external power supply to deliver power to HDD. then only option left is to use Rpi4. so yeh you can Raspberry pi 4

I-MAN
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What I've found over the course of a few years is that having one external HDD/SSD permanently plugged directly into USB works fine on Pi4 both with the blue 3.0 slots or the black 2.0 slots, but plugging a second HDD or SSD drive is unreliable and a soon as some intensive read or write operation requires more peak power than the unit can provide you run into issues and the mount is lost.

This is especially true when both drives are in intensive read/write mode. Given that USB 3.0 is able to conserve power when devices are in idle mode I'd speculate that you might be able to plug in two USB drives and copy from Drive A to the sdcard while Drive B is idle, but copy or move from Drive A to Drive B will result in one or both of them being disconnected.

To sum up: one unpowered USB/SSD drive is fine, if you plug the second one you are likely to run into trouble and possible data corruption. No issues with USB flash sticks though, as those require less power.

ccpizza
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