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Powered USB hub that doesn't power from the PC if its available first ? Answered

Odd problem. I'm trying to find a USB hub that does NOT ennumerate when the external power isn't connected to the hub. All I've tried so far do their best to supply the connected items with what's available. I have devices attached that need more than 100mA, can't get it, and freak out.

I've tried a standard hub, and cut the USB +5 from the PC, which stops the things ennumerating sure, but they don't ennumerate when you plug the power in !

I suppose I COULD put a signal relay in, or logic that would do it, but something off the shelf would be better.

TIA gang




Best Answer 8 years ago

A quick search - someone posted this:  halfway what you want - unpowered switched hub...


just a thought, im not familiar with these power provider boxes, do these USB power plant things have any common grounding with the computer USB port? ive found in the past that trying to get two different components to talk to eachother without a common ground wire is tricky, even if the two components use the same protocols and transmission rates, apologies if this drifts off the subject a little

.  Could you use something like a headphone jack that disconnects the speakers when headphone are plugged in (switch that is opened by the tip of the plug).

.  That was pretty vague, wasn't it? :)
.  What I had in mind is replacing the power plug/jack on the hub with something that has a built-in switch. When the power jack is unplugged, the switch kills the 5V from the computer.

Hi Nacho,

I've got a unit where I've consolidated all 7 USB items into one hub. The unit is sometimes not switched on when the PC is, it would be a real PITA to have to disconnect the USB cable each time its used.


.  I'm talking about replacing the power jack and plug with "headphones style" units and using it to switch 5V on the USB when you insert/remove the power plug.

Agreed with the asker that most usb hubs work in 'un-aided power' mode...I've heard of some that people complain dont work unless you power the plug up and only because thats an annoyance to them.

If you want it to stop enumerating, usb is hot plug, and the computer is relatively dumb to the power lines (other than current limiting), so run the data lines through a physical switch.  To automate things, make that switch a low voltage relay powered by the incoming power from the wall adapter.  power on, connects usb data, computer sees device.  Unplug, and it disconnects.

Agreed also that a ready-made solution would be best, but I can't suggest any specifically for this behaviour.

Posted a request for suggestions on this on the dealextreme forums - if anyone can find it, china can.