Reverse charging (Android phone)

[at0m11c]

What would happen if I select reverse charging on my phone while connected with an USB-C cable to my desktop computers USB port?

 

I ask this because im curious if i would break something if I somehow selected this option. I mean sending out a current into an USB port on a desktop computer does not sound good hehe.

[WereCatf]

You can't push current into a device, the device has to pull it, if both devices are at the same voltage-level; the USB-ports on desktops and laptops are generally protected against reverse current up to something like +6V or +8V, so nothing would happen. If your phone supplied higher voltage than that, then yes, you'd be damaging your USB-ports, because you'd be overcoming the protection. That would, however, violate the USB-standard as it generally goes only up to +5.2V to counter voltage-drop in wires.

 

EDIT: Clarified a bit.

[at0m11c]

17 minutes ago, WereCatf said:

You can't push current into a device, the device has to pull it, if both devices are at the same voltage-level; the USB-ports on desktops and laptops are generally protected against reverse current up to something like +6V or +8V, so nothing would happen. If your phone supplied higher voltage than that, then yes, you'd be damaging your USB-ports, because you'd be overcoming the protection. That would, however, violate the USB-standard as it generally goes only up to +5.2V to counter voltage-drop in wires.

 

EDIT: Clarified a bit.

Thank you  for explaining

 

So the worst scenario is that the USB port gets damaged?

 

It could not damage other parts of the desktop computer ? 

[WereCatf]

Just now, at0m11c said:

So the worst scenario is that the USB port breaks?

 

It could not damage other parts of the desktop computer ? 

It could, depending on how the motherboard is built and how high voltage you're supplying, but usually the damage only reaches up to the USB-controller. It could destroy more, so I don't recommend you try, though -- you just never know how well the protection-circuitry has been developed and what sort of failure-mode the USB-controller will exhibit.

 

I don't know if you're familiar with "USB-killer" type sticks certain companies sell, but they generate a very high voltage reverse spike in an effort to cause damage -- in most cases that I've seen, only the USB-ports have stopped working, but there have been some laptops where the motherboard got fried too bad for it to work at all anymore.

[at0m11c]

1 minute ago, WereCatf said:

It could, depending on how the motherboard is built and how high voltage you're supplying, but usually the damage only reaches up to the USB-controller. It could destroy more, so I don't recommend you try, though -- you just never know how well the protection-circuitry has been developed and what sort of failure-mode the USB-controller will exhibit.

 

I don't know if you're familiar with "USB-killer" type sticks certain companies sell, but they generate a very high voltage reverse spike in an effort to cause damage -- in most cases that I've seen, only the USB-ports have stopped working, but there have been some laptops where the motherboard got fried too bad for it to work at all anymore.

Oh,ok. Yes I know about USB-killer.

 

I mean if this option can damage a computer like this it should be an extra layer of protection before you accidently select the "reverse charging option". Maybe I am overthinking and it takes some time until it really gets damaged or maybe nothing will get damaged at all hehe.

[WereCatf]

2 minutes ago, at0m11c said:

I mean if this option can damage a computer like this it should be an extra layer of protection before you accidently select the "reverse charging option". Maybe I am overthinking and it takes some time until it really gets damaged or maybe nothing will get damaged at all hehe.

No, the option on your phone won't damage anything. It is a USB-port and its voltage is limited to around +5V and, like I said, all modern laptops and desktops already have reverse-current and over-current protection to something like +6V or +8V -- your phone would have to produce a much higher voltage than +5V on the USB-port to actually damage anything, but that would mean someone specifically wanted to make a phone that can damage computers, and no sane manufacturer would do that.

[at0m11c]

2 minutes ago, WereCatf said:

No, the option on your phone won't damage anything. It is a USB-port and its voltage is limited to around +5V and, like I said, all modern laptops and desktops already have reverse-current and over-current protection to something like +6V or +8V -- your phone would have to produce a much higher voltage than +5V on the USB-port to actually damage anything, but that would mean someone specifically wanted to make a phone that can damage computers, and no sane manufacturer would do that.

You are the man, thank god there is smart people out there!