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I just got a WD MyPassport external drive, that is solely powered via USB (there are no other plugs).

I have seen in various places that a powered USB port is suggested for the RPi, but I can't quite tell if that is referring to powering the Pi itself, or if you buy a powered USB strip, and plug that in to the Pi and then plug the External Drive to the power strip. And then leave the Pi itself powered by MicroUSB to the wall plug.

If I do need a powered USB, what specification do I need to look for? There are tons online, but only via amazon comments can I check if the RPi works with these -- and again there, I think people are referring to powering the Pi itself from the strip - not peripherals like HDD/Keyboard/etc. Would this work, or this Amazon one?

From what I understand, I don't need it to Backpower since I'm using the designed MicroUSB port to power the pi. Yes?

Thanks for any clarification on this!

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    You can probably do either, it depends on how much the hub can provide to each of the ports. The difference with a hub is that the HD is powered (mainly) by the hub and not (only) by the Pi. As to your question, the drive seems to need 0.5A, so assuming you have a standard RPi power supply, and no other extra hardware, you probably do not need a powered hub. – Tomas By Mar 28 at 15:53
  • @TomasBy - How much power should I look for the ports to provide? (I haven't found any power info on the WD drive itself ...but is there a general guideline to what I'd want my ports to provide? Is 900MA enough?) – BruceWayne Mar 28 at 15:58
  • @TomasBy I'm powering the Pi with the standard pi charger via microusb and just want to make sure my external drive is getting enough power so I can leave it plugged in to the pi – BruceWayne Mar 28 at 16:13
  • (@TomasBy - Where'd you find the WD Drive needs 0.5A. I thought I am decent at Google-Fu, but can't seem to find anything official on the power it needs.) – BruceWayne Mar 28 at 16:41
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    Actually, it is 3.0 so maybe it needs slightly more. Then I guess you need a hub. Max current over USB 3.0 is 0.9A apparently, so 0.9 is what you need the hub to provide then, per port. – Tomas By Mar 28 at 16:47
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I have a RPi 3B+ (among others), and I have used them successfully for long periods of time with WDPassport drives plugged directly into a RPi USB port (i.e. not in a powered hub). However, the WDPassport units I use are compatible with USB 2.0 only, and not USB 3.0.

Your question contains a link to a WDPassport device that is compatible with USB 3.0 and USB 2.0. To my thinking, there's nothing to be gained by using a USB 3.0 device with a Raspberry Pi because the USB ports on RPi are USB 2.0. Further, this article suggests that USB 3.0 may use more power, but of course it doesn't have to do so. Also, it's not clear what it means for the device's power requirements when that device is declared to be compatible with both USB 2.0 and 3.0.

I've tried to find power specs for the WDPassport several times over the years, but I've been unable to find any specifications published by the manufacturer. Consequently, I'm unclear as to whether or not your chosen model of WDPassport will need a powered hub to operate properly with the RPi.

Due to this uncertainty, my answer is this:

Use USB 2.0 only devices with the RPi whenever possible

If that's not possible, and you can't be certain you won't exceed RPi's power capacity (600 mA), then a powered USB hub is the safe bet. Note that it is possible to up that limit to 1.2 A, but your mains-connected supply must be capable.

  • Thanks very much for this great info! Since my WD is a USB 3.0 one (I can't really return it anymore), perhaps using a powered strip is the way to go. Looking around too, it looks like USB 3.0 external drives are becoming the majority. Any final ideas on what strip specifically, or at least what data to look for? I assume the powered hub should have output of at least 900mA per plug, yes? – BruceWayne Mar 29 at 16:50
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    If you get a hub that meets the USB 3.0 specification, you'll be fine. – Seamus Mar 29 at 16:53
  • Thanks Again! To be explicit (for myself), if I plug my WD into a powered hub, anything else I plug in to the pi directly (webcam, keyboard, etc.) will just use the Pi's power and I shouldn't have issues? (A random note - is it not surprising that we can't find specific info on WDPassport drives from the manufacturer? Or is that relatively common with hardware companies?) – BruceWayne Mar 29 at 16:54
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    I don't know if it's surprising, but it is aggravating. I suppose they can justify that for USB-compliant devices since USB has its own set of power specs, and as it's a standard they will comply with that. Unfortunately, I have neither the time nor inclination to read the USB spec to get the simple answer I need. – Seamus Mar 29 at 16:58

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