External Hard Drive to Smartphone without additional power supply

Question

I) Goal

Use external hard drive without power supply - no hub either - to backup smartphone directly.

II) Configuration

Huawei Mate 20 Pro, this - I own this.

USB C male to USB A (3.0) Adapter (i.e. OTG adapter), this - I own this.

any of the following external hard drives:
- WD ELEMENTS PORTABLE 4 TB WDBU6Y0040BBK-WESN - I think about buying this.
- LaCie Rugged Mini 4 TB LAC9000633 - I own this, brand new & ExFAT formatted.

III) Problem

I don't know the power output of my smartphone or the power requirements of those hard drives exactly and am therefore not sure if my goal is achievable. When I connect my LaCie 4TB to my phone - via said USB-C-A-Adapter or directly via a USB-C-cable - the drive is not recognised and doesn't seem to spin.

IV) Known information / How I am trying to solve my problem

According to this and this my goal is achievable, according to this (Android Enthusiasts) maybe not.

I searched the web, but didn't find any official/trustworthy information from the manufacturers, from sellers or from users about the power in or output of either of those devices. The following information regarding the HDDs I found seems somewhat ambiguous:

WD = 1 watt (WD on Amazon, somewhat trustworthy, but only info about 3TB version, here).

LaCie = max. 2.9 watt (quite trustworthy actually, here).

My smartphone is able to supply an Apple Keyboard (wired) and an Apple Mighty Mouse (wired) at the same time over said OTG Adapter and a USB hub (hub power supply not plugged in!)... But I don't know the power consumption of those peripherals.

V) Main Questions

A) Is my goal really achievable? How?

B) Is my assumption right, that my LaCie HDD won't spin because of power supply issues?

C) Will the mentioned WD HDD do the job? If no, other suggestions, please.

D) How do I have to format my drives to be read by Android? (I've read ExFAT should work...)

VI) Additional, optional Questions

E) What are the actual power requirements (in watt) of those drives? What is the actual power output of my Smartphone over OTG? Maybe someone with experience (and/or who has these drives) knows those numbers? Don't bother looking into the spec sheets of those drive, there is no information about the power requirements in there.

VII) Disclaimer

I know, these aren't questions directly regarding Android. But,

first, there is no Stack Exchange Site about Smartphones,

second, I was sent here by the people of the Electrical Engineering Stack Exchange Site after posting this very question there (and deleting it now),

third, my smartphone is an android device,

forth, this might be a Android-ExFAT format problem (?),

and fifth, the Android community is really competent when it comes to tech questions,

so this is the right place for this, I think... Please don't hate on me for posting my questions here - I shall kindly migrate to another Stack Exchange forum if you know a more suitable one.

Many thanks.

VII) Update

Confirmed by Huawei support: The Mate 20 pro has 1 Ampere / 5 Volt output.

Confirmed by LaCie support: Said LaCie Drive - and as it seems every thing hooked up via USB 3.0?! - needs 0.5 Ampere (no voltage info) to function properly. - So why doesen't this work? Too low voltage?

— CJLM | Sources

Answer

A) Is my goal really achievable? How?

Unsure, see the answer to the second question of item E.

B) Is my assumption right, that my LaCie HDD won't spin because of power supply issues?

Yes. The HDD isn't spinning up because the power supply isn't sufficient.

Another reason would be the HDD being broken otherwise, but this is unlikely the case given your very detailed description of your problem.

C) Will the mentioned WD HDD do the job? If no, other suggestions, please.

For the same reason as B, this is unlikely. 2.5" HDDs nowadays have a fairly similar power consumption, regardless of brand. Older HDDs and HDDs with higher capacity tend to draw more power, but not making a huge difference.

D) How do I have to format my drives to be read by Android? (I've read ExFAT should work...)

Nothing. You're done it correctly - exFAT is the right filesystem for them.

E) What are the actual power requirements (in watt) of those drives?

As given in whatever you've read. Those claimed power requirements are usually correct.

What is the actual power output of my Smartphone over OTG? Maybe someone with experience (and/or who has these drives) knows those numbers?

So, this is the most tricky part...

I haven't used any Huawei phones, but from my past experiences phones don't output much power (usually less than 2W) to OTG devices. It's likely that your phone is doing the same - not supplying as much power as needed by the HDD.

From previous news (in my local language Chinese - sorry), Mate 20 / Mate 20 Pro is capable of running as a power bank, or "reverse charging". I'm guessing that the claimed 5V/1A output is only achievable in reverse charging, not OTG.

The conclusion is not quite delighting - you have to get some kind of external power supply before you can use your HDDs with OTG.

— iBug | Sources