Quest 2 original link cable back feeding power to PC. Anyone else experiencing this?

LGabrielPhoto

2[H]4U
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Jan 5, 2006
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So, this is odd...yesterday I forgot to disconnect my Quest 2 from the original USB Type C cable and noticed that my Mouse and my Blaster X3 had flickering lights as if they were receiving some power still even though my PC was off.
I even unplugged the power cord and still the same..that REALLY got me confused. Then I disconnected the Quest 2 and the lights when off on the mouse and Blaster X3.
I tried the Quest 2 with a different cable connecting to another USB port (not type C) and did not experience the issue.
I also tried that same cable that worked fine with a type C adapter and again NO issue. Only when using the original Quest 2 link cable I get that back feeding power weirdness.

Anyone else?
 

bobzdar

[H]ard|Gawd
Joined
Jun 6, 2003
Messages
1,835
So, this is odd...yesterday I forgot to disconnect my Quest 2 from the original USB Type C cable and noticed that my Mouse and my Blaster X3 had flickering lights as if they were receiving some power still even though my PC was off.
I even unplugged the power cord and still the same..that REALLY got me confused. Then I disconnected the Quest 2 and the lights when off on the mouse and Blaster X3.
I tried the Quest 2 with a different cable connecting to another USB port (not type C) and did not experience the issue.
I also tried that same cable that worked fine with a type C adapter and again NO issue. Only when using the original Quest 2 link cable I get that back feeding power weirdness.

Anyone else?

It actually probably depends more on the motherboard - some have always powered ports and others aren't, which the usb-c apparently is setup on your board to also allow power input (like laptops that allow charging via the usb-c port). The Quest cable is dumb, so unless they put a diode on the power pin (which would make it work only in one directtion) it doesn't matter. This is something that might be fixable on the Quest 2 itself, but they may have intentionally allowed it to power other devices so accessories could be plugged in there at some point. There may be a bios setting to disable that on the usb-c port, unsure.
 

sharknice

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2,412
I think this happened to me too. I had mine plugged into my PC (which was powered off) to charge overnight but when I grabbed it to play the battery was drained. I thought I just forgot to turn it off or something, but it could have been what you're describing. After that happened I started plugging it into a power socket instead.
 

Chief Blur Buster

Owner of BlurBusters
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It actually probably depends more on the motherboard - some have always powered ports and others aren't, which the usb-c apparently is setup on your board to also allow power input (like laptops that allow charging via the usb-c port). The Quest cable is dumb, so unless they put a diode on the power pin (which would make it work only in one directtion) it doesn't matter. This is something that might be fixable on the Quest 2 itself, but they may have intentionally allowed it to power other devices so accessories could be plugged in there at some point. There may be a bios setting to disable that on the usb-c port, unsure.
On proper USB-C cables on proper USB-C ports, there is a software handshake protocol to "negotiate" the Power Delivery (USB PD) direction as well as agreed-upon voltages. Some ports even are programmable power supply (USB PD PPS) negotiating voltages in millivolt-league increments from 3.3V to 20V.

Dumb adaptors & simpler cables don't do this, it has to be true full USB-C compliant from end to end -- then this shouldn't happen.

USB Power Delivery is a programmable power protocol, which is quite neat from a software engineering perspective.

(BTW, did you know a USB-C PD wall wart has more computing power and memory built into it than the Apollo 11 moon mission computer?)

I think this happened to me too. I had mine plugged into my PC (which was powered off) to charge overnight but when I grabbed it to play the battery was drained. I thought I just forgot to turn it off or something, but it could have been what you're describing. After that happened I started plugging it into a power socket instead.
If your computer was turned off and you were using a proper USB-C cable, it was probably the battery. The Quest 2 is sometimes iffy at turning itself off automatically.

However, bad cables that are not fully USB-C compliant may indeed backfeed.

If you are using an active extension cable that's not USB-C, I had one that was backfeeding its power into the computer (keeping some computer fans running even when the computer was unplugged). For one of my 33 foot USB3 cables for one of the sensors with my original Rift, I had a crappy active extension cable used a power adaptor at the end, but that backfed 33 feet all the back to the computer. I switched from UGREEN (backfeed problem) to a better brand, Plugable (had backfeed protection). That stopped the weird "some computer fans kept running even for unplugged computer" problem.
 
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Nobu

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Jun 7, 2007
Messages
5,917
My phone will (try to) power stuff with an Anker USB-C cable. LEDs will flash on and off on my Asrock x570 itx board.
 

Chief Blur Buster

Owner of BlurBusters
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My phone will (try to) power stuff with an Anker USB-C cable. LEDs will flash on and off on my Asrock x570 itx board.
Hopefully the phone asks you first before trying to blindly deliver power to a non-negotiating sink (i.e. a USB client that's powered off).

As far as I know, non-negotiating sinks only gets 5V at a few hundred milliamps by default -- just enough to power an accessory (like a mouse or a keyboard or an Ethernet adaptor) to wake it up to begin handshaking over USB (to ask for a different voltage and/or get much higher power).

Now that I think about it -- The USB-C on a Quest 2 supports keyboards(!) & Ethernet adaptors and certain other USB-C accessories -- so to successfully do that, it indeed has to support outputting at least 5V 100mA (minimum) blindly before the Power Delivery protocol starts -- active negotiation of power.

If it's doing that to a computer -- then that may explain things. A slow power drain of the power intended to wake up USB accessories, rather than charging power (as OP suggests). Still drains the Quest 2 battery either way. However, a powered-up computer with a good power+data cable, will keep my Quest 2 charged. I guess the moral of the story is to use a good cable + keep computer powered.
 
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