Question Asus Zenscreen charging from different source than video ?

Oct 23, 2021
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Hi,

I have an Asus Zenscreen MB16AMT portable monitor and connect it to a Moto G100 phone via a USB-C and the "ready for" feature which I understand to be basically DisplayPort. It works well, including the touchscreen functionality.

However in this configuration, both the phone and screen have to run from their respective batteries.

Has anyone found a way to link the phone and screen for video+touch, while simultaneously providing power to both devices from another source (eg mains charger or USB battery bank)?

Cheers

Anton
 
Oct 23, 2021
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Quick update on this, I found a relevant Help article:

https://motorola-global-portal.custhelp.com/app/answers/prod_answer_detail/a_id/157706

"Most external displays with USB-C or HDMI ports charge your phone while in the dock. If your external display’s USB-C ports don’t output power, connect the display to a powered USB-C hub, then connect the hub with the dock."

I presume that normal USB hubs have a defined "master" port (ie normally the one connected to a laptop) and then multiple other USB sockets for the devices (eg memory sticks). When it says a "powered USB hub", does that mean just any hub that takes power in on a dedicated connection (mains or USB charger?) without that same connection becoming the video/data master? Or is there further spec I need to worry about here?

Cheers
 
Oct 23, 2021
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I ended up going for a trial and error approach and think I worked out the requirements, sharing here for anyone else who is confused by this.

Your options are
1) You could probably buy a USB screen with pass-through charging such as the Lenovo Thinkvision M14 or M14t. It has two USB ports and you can plug a high power USB PD charger (eg your laptop charger or possibly a very high spec battery bank) in to one end, and then link your laptop or Ready For phone in to the other end. Both devices will be charged/powered from the mains. Unfortunately this screen is not compatible with my laptop so I didn't get this or test it.

2) Failing that, USB hubs:
On all types of USB hubs, there is normally one specific port that connects to the host/master (laptop or G100 phone in this case) and then other ports for you to plug in your peripherals etc (mouse, keyboard, USB screen). Powered USB hubs have an additional port for power IN from an external source however most of the basic ones DO NOT send any power to the master (phone/laptop) port side at all, only to the peripherals.

Most of the powered hubs I found that DO pass power to all ports including the host are ones designed for pass-through USB-PD, for example to charge a laptop with its USB-C charger through the hub whilst also connecting and powering peripherals to the same hub. The USB-PD standard is not fully compatible with QC3 ('turbocharging') but both USB-PD and QC3 are backwards compatible to basic USB (+5 volt). The biggest chargers (such as the one bundled with the G100) can give 3A at 5V, meaning a total power availability of 15W - not so huge but absolutely sufficient here.

I tried two USB-PD hubs with the standard Motorola charger (5V 3A USB) as I don't own a USB-C PD charger. Neither hub worked perfectly:

i-tec USB-C Metal Charging HUB 4x USB 3.0 + Power Delivery 60W - link
This did not work at all. It's not obvious from the product page but in the manual it's indicated that it needs at least a spare 10 or 20W after powering the peripherals before it will decide to send any power to the host. So it didn't send power to the phone, but nor did it work when using it unpowered (ie both phone and screen running from their respective batteries).

UGREEN USB C Hub HDMI 7-IN-1 Type C Hub with Power Delivery, USB 3.0 Ports, TF/SD Card Reader, 100W PD Charging - link
This successfully powered both the screen and phone simultaneously. However, only power and touch were sent along the USB-C line - not video. Therefore the screen was useless until I also connected the HDMI port of the hub to the screen video in. At that point, I had video along the HDMI, power in and touch commands out along the USB-C. This all worked quite well and with the 3A charger there was plenty power to keep both devices charged while in use. However, if I unplug the power supply then rather than both devices switching to battery, the phone tries to power everything and of course fails. Nonetheless of course in this case I can remove the hub and just directly connect the two devices together.

For me this is OK, but if your screen only had a USB-C input (no HDMI) such as the ASUS ZenScreen MB16ACE then this would probably not solve your problem. Likely you need an even fancier hub that explicitly supports DisplayPort or something, or perhaps just plenty more power with a PD charger.
 

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