On Mon, 8 Oct 2018 02:49:19 +0000 (UTC), bob prohaska
 wrote:

>Jan Panteltje  wrote:
>>
>> My old 1TB Seagate USB has its own wall-wart marked as 12V 2A,
>> makes 24 W.
>> My new small 'Platinum' 1TB USB disk needs 2 USB ports for power,
>> USB is rated at < 600 mA, so estimate 1A at 5 V is 5 W.
>> The Seagate spins down after a while not use.
>> Not sure about the other one,
>> use it on the TV for movies mainly.
>> The Seagate has all the raspi backups,
>> maybe using USB drives with external supply is safer with raspi.
>
> It's understood that "normal" USB hard drives can't be powered
> directly from the Pi and require a separate power supply. I just
> started wondering if anybody is making ultra low power mechanical
> drives that _could_ be powered directly from the Pi's USB port.
>
> A 2.5" drive that drew little enough power to be driven from the
> Pi might be a viable alternative to flash storage. Is there such
> a beast? 64G or 128GB would be large enough, 32 GB is  slightly
> too small.

I have a 1 TB Toshiba 2.5" portable USB drive connected to a Pi
3B, running all the time (datalogging and bittorrent).

At first I tried to power it with a Y cable from a separate
power supply. That failed, somehow the two power supplies fight
and fail to regulate properly (back feeding?).

Now it is powered by a Pi 3B's USB port and draws 500 mA.
At power up
That works fine, but to prevent the low power warnings (yellow
lighting bolt) it is essential that the cable between power
adaptor and Pi has a very low resistance.

The power cables of most adaptors are too long and too thin to
work properly. The buffer capacitors in the Pi are tiny, and
can't can't handle short peaks in demand very well.

So I bought short cables with just power leads (no data) and AWG
18 gauge for all my Pi's. These aren't the cheapest, but they
work fine.

Search on eBay for:
15cm 0.5FT Micro B USB Fast Quick Charge Cable 2.1A Android
SmartPhone 18AWG
30cm 1FT Micro B USB Fast Quick Charge Cable 2.1A Android
SmartPhone 18AWG NEW

HTH
--
Regards,
Kees Nuyt

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