USB 3+ power outputs Confusion

DWD1961

[H]ard|Gawd
Joined
Nov 30, 2019
Messages
1,314
So, you can use a USB 3 cable and plug it into a charging port for something like 60 watts, but you never get that from the back of your computer. I think the back board USB 3 ports are 900mA.

I'm assuming that when using a powered hub, the USB connector is supplied with more power that is then passed on to a device that can use more than 900mA?

Also, is there a standard for motherboard USB 3+ output power? I think it is 900mA? Is thta jsut a standard for motherboards due to restricted power capabilities/cost?
 
It all depends on how the designer of the charger/hub/laptop/desktop/etc. decide to offer through the port(s).

Pretty sure the standards for USB power output can be found on sites like Wikipedia, among others.
 
It all depends on how the designer of the charger/hub/laptop/desktop/etc. decide to offer through the port(s).

Pretty sure the standards for USB power output can be found on sites like Wikipedia, among others.
You would think, but not. For instance, a USB cable can carry a lot more than 900mA at 5V, as we see with 65 watt 5V chargers. However, I think for device side connection, the most you will get is 900mA.
  • Charging port vs Device connection (Where a device receives data, not just power)
That's my confused understanding of it currently. I think I might buy a USB ammeter/voltage meter box so I can test myself. I wish they ah one where i could plug in my multi meter instead of relying on their units measurements..
61vWPpqarhL._AC_SL1500_.jpg
 
You would think, but not. For instance, a USB cable can carry a lot more than 900mA at 5V, as we see with 65 watt 5V chargers. However, I think for device side connection, the most you will get is 900mA.
  • Charging port vs Device connection (Where a device receives data, not just power)
That's my confused understanding of it currently. I think I might buy a USB ammeter/voltage meter box so I can test myself. I wish they ah one where i could plug in my multi meter instead of relying on their units measurements..

You couldn't have looked very hard:
https://en.wikipedia.org/wiki/USB#Power-related_specifications
https://en.wikipedia.org/wiki/USB#Power
https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery_(USB_PD)
https://en.wikipedia.org/wiki/Quick_Charge

There are no 5 V chargers putting out 13 A to provide 65 W. Any USB port putting out that much power is probably negotiating 20 V with the sink (depending on the standard used).

And as I said before, how much power a USB port is able to put out is up to the manufacturer.
 
You couldn't have looked very hard:
https://en.wikipedia.org/wiki/USB#Power-related_specifications
https://en.wikipedia.org/wiki/USB#Power
https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery_(USB_PD)
https://en.wikipedia.org/wiki/Quick_Charge

There are no 5 V chargers putting out 13 A to provide 65 W. Any USB port putting out that much power is probably negotiating 20 V with the sink (depending on the standard used).

And as I said before, how much power a USB port is able to put out is up to the manufacturer.
Yeah, no way the 5v/13A calc. My error.

However, my original point was talking about motherboard power output per USB 3+ port.What would the spec be for a motherboard manufacturer's USB 3 ports, since the Wiki pages say a USB 3 "device" is max 900mA "draw" but a motherboard isn't a device drawing, but a supply. So what spec limits the output?
 
Yeah, no way the 5v/13A calc. My error.

However, my original point was talking about motherboard power output per USB 3+ port.What would the spec be for a motherboard manufacturer's USB 3 ports, since the Wiki pages say a USB 3 "device" is max 900mA "draw" but a motherboard isn't a device drawing, but a supply. So what spec limits the output?
Motherboards will limit the current.
 
Motherboards will limit the current.
What is the current for motherboards? Devices can use "up to" 900mA, but that doesn't tell us what the output is, if there even is a spec for it. I'm assuming that the minimum for a USB 3 port is 900mA. And, that's what the ports deliver on a motherboard, although they could do more.

So, that's really my question. MB USB output.
 
What is the current for motherboards? Devices can use "up to" 900mA, but that doesn't tell us what the output is, if there even is a spec for it. I'm assuming that the minimum for a USB 3 port is 900mA. And, that's what the ports deliver on a motherboard, although they could do more.

So, that's really my question. MB USB output.

The spec talks about device current because it’s the device that determines how much current is needed. It provides a minimum design current that a host has to safely provide to each port. There would be no logical reason to specify a maximum current for the host.
 
The spec talks about device current because it’s the device that determines how much current is needed. It provides a minimum design current that a host has to safely provide to each port. There would be no logical reason to specify a maximum current for the host.
Sound right. Guess I'll have to contact Gigabyte to see how much power they supply through USB 3. At this point, I'm assuming they supply the standard 900mA and that's it.
 
I found this. It's stand alone and doesn't install. I'm going to try it.
https://www.nirsoft.net/utils/usb_devices_view.html
Shows power usage per USB device. However, it's only going to report in increments of the package current, not actual mA's since I assume that's what Windows reports and that's how the program issues it's readout. We'll see how it breaks it down.
 
On a related note, how come my Pixel phones, with Anker A-to-C cables, will rapid charge so unreliably? I've had two cables now that both used to, and now will only slow charge. It almost feels like software patches are blocking this as the cables aren't damaged or abused much at all.

This never happens over C to C but it's annoying as hell since there's not exactly a ton of C ports everywhere I go and slow charging is like 6 hours from 20% to full.
 
On a related note, how come my Pixel phones, with Anker A-to-C cables, will rapid charge so unreliably? I've had two cables now that both used to, and now will only slow charge. It almost feels like software patches are blocking this as the cables aren't damaged or abused much at all.

This never happens over C to C but it's annoying as hell since there's not exactly a ton of C ports everywhere I go and slow charging is like 6 hours from 20% to full.
Voltage drop across the cable is possibly too high and the charger falls back to spec?
 
On a related note, how come my Pixel phones, with Anker A-to-C cables, will rapid charge so unreliably? I've had two cables now that both used to, and now will only slow charge. It almost feels like software patches are blocking this as the cables aren't damaged or abused much at all.

This never happens over C to C but it's annoying as hell since there's not exactly a ton of C ports everywhere I go and slow charging is like 6 hours from 20% to full.
It could be a phone problem. Try a different cable and brand, and try your cable and charger that came with the phone. I'd also start a new thread for that specific problem.
 
Back
Top