Powered usb hub giving voltage to motherboard?

[Hemispasm]

Hi there

Just purchased a small usb hub (x4) that is powered up by external source (not just the usb from the mobo), since i have more than 10 usb devices attached altogether and sometimes there was not enough current from the mobo to the old hub (with no external power source) that i used to have.

Now what i noticed when i plugged the usb cable of the hub to the mobo with the PCbeing closed, was that suddenly the three 8' fans that i have in the case plus the lead from the 12' fan of the cpu started working! With the PC closed. When i disconnect the hub from the computer this stops. It also stops when i disconnect the hub from its power source leaving only the usb attached to the mobo.

Somehow it seems like current is being transferred to the mobo while the PC is closed by the hub - and i don't know why or whether it is safe. Is it?

[Whappo]

I don’t believe the USB hub is suppying power “to” the motherboard.
I’m guessing that when you say the PC is closed you mean shutdown? One way to be sure is to disconnect the power cord from the PC and then plug the hub into it and see what happens. Another thing, some motherboards have a “wake on usb” option in the bios for use with remote control devices. You might check to see if you have that option in your bios and if it’s enabled. Not much more I can think of right now.

[Hemispasm]

Yes i mean shutdown.

The 8’ fans start working even when PSU switch is off, as long as the hub is connected to AC. I can not figure it out either. They stop only when i disconnect the hub from the AC. I will check the bios setting you mentioned - i am pretty sure i have it disabled but i will double check. I will lso check by disconnecting the powercord completely. But even so, why would the fans start working like that?

Thanx for the help.

[xtacydima]

Hemi, you got a multimeter?
if not, try this hub on another pc or laptop, maybe its defective and giving feedback… if you have a multimeter, its easy to measure this.

[Hemispasm]

Thanx Dima

Nope i dont have a polymeter (multimeter, arg my greek) here, but i have bought another one of these for a friend, i will use that too and see what happens. The bios option btw is disabled. The PC is running for a couple of days wiith no problem so far.

[Hemispasm]

I finally checked the other usb hub my friend had, it also does the same thing. I am currently running without power to the hub, till i figure this out or buy a new one. Thanx for the help.

[Ibex]

I have come across this problem before, it seems to be common with cheap USB hubs. I have never had the courage to use the power supply that came with mine!

[Hemispasm]

Ok, thanks for letting me know, its nice knowing that it’s not just in my mind