[sdiy] USB power (slightly off-topic)

[Jason Tribbeck]

Hi,

Funnily enough, the last electronics I did at my previous company was a
6-port USB hub that supported either 2A or 3A per port (it was a system
that was to charge multiple mobile phones whilst allowing a computer to
communicate with them to direct them to test mobile infrastructures).

Unfortunately, the project was canned after I did the first bit of CE
testing (which failed abysmally as I hadn't realised I had created a ground
loop that happened to be the same wavelength as USB 2 data transfer
speeds). I was in the process of being canned myself anyway, so I didn't
really worry about fixing it (the company decided it didn't want to do
hardware any more).

David's answer is probably the best, but you need to be careful not to
disturb the impedence of the D+ and D- signals too much.

Although another possibility is to use some 3.5" USB to SATA enclosures -
they tend to have an external PSU, which should provide ample power.

A further possibility is to use a SATA data+power extension cable between
each of your adaptors and drives, and replace the power with judicious
cutting of the cable.


On Tue, 8 Nov 2022, 19:28 Rutger Vlek via Synth-diy, <
synth-diy at synth-diy.org> wrote:

> Dear list,
>
> I hope you don't mind me tapping into our collective list wisdom for
> something slightly non-synth related. The case is as follows:
>
> I'm building a NAS at home from a Raspberry Pi 4B and a couple of SSDs.
> The SSDs are connected to the Pi via a SATA-to-USB converter. They work,
> but stop working when used intensively. Not to my surprise, because the
> power requirement of the drive is 1.7A at 5V each. The Pi USB ports can
> only deliver 1.2A at most (and shared between 2 ports). So I need a more
> beefy supply. My initial idea was to buy a couple of these USB Y-cables
> that have two USB-A connectors on one side, allowing the user to provide
> the paralleled power of two USB ports. However, even on a single port, the
> Pi already reaches it's limits. So I thought, why not plug the second USB-A
> plug of the Y-cable into a USB-charge, so that it can provide all the
> current needed by the drives. However, I have a bad feeling about this...
>
> I don't have a clue about the internals of a typical USB Y-cable, and have
> not been able to find any datasheets on them. In the worst case, power from
> the Pi's USB port would just be connected directly to the power output of
> the USB-charger, and that does not sound like a good idea. They might not
> be at the exact same voltage, and I since both of them are SMPS's, I don't
> know if they'll somehow start interfering with each other. If only there
> would be some series diodes internally present in the Y-cable, but I have
> no clue if there are... Does anyone know (or can measure)?
>
> Plan B was to buy a powered USB hub, but I struggle to find one that can
> deliver the required 1.7A at 5V on multiple of its ports at the same time.
>
> Plan C, that just came to mind, is that I might be able to find a beefy
> USB PSU with multiple ports, that I can use to feed the Pi from, as well as
> the drives via Y-cable. The Y-cable would then be combining the power from
> Pi's USB output with the direct output of the same PSU. Would that work?
>
> Plan D would be to make my own power distribution board, where USB
> connectors pass data between the Pi and the disks (but no power), and power
> is injected from a DC barrel plug (and some filtering)
>
> What do you think would be the best approach?
>
> Rutger
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