USB Hub - Possible Power Problems?

bradavon · Post by **bradavon** » 15 Jan 2007, 19:25

I have a 4-Port USB Hub and a friend has a 2-Port USB Hub inside the stand of his monitor.

Both seem to have power problems, the 2-Port one Windows XP even said once it was having power problems. USB Sticks aren't recognised by Windows through it but a printer works. On the 4-Port USB Hub if I plug it in via two USB ports so it's got twice as much power it allows a USB 2.5" hard disk to work but nothing else (it has 3 free ports still), with only 1 USB port used the hard disk won't work.

This is at the same time the 4-Port USB Hub at least has packaging which specifically states no AC adapter is needed, it's self powered. I do wonder why it has an AC adapter plug on the side if that's really true (although it conveniently doesn't say what the voltage is).

I've heard a few times that USB Hubs are supposed to be Self Powered but I've found this to in reality be much the opposite.

What am I doing wrong?

Lourdes · Post by **Lourdes** » 16 Jan 2007, 03:19

USB can supply 500mA in 100mA increments, with a hub this is 400mA because the hub needs some. Some devices need 500mA alone so they can't be run from a hub.
I'm not sure why you're having problems. It may be that the hubs are designed for less pwoer or a USB bus issue. I'd try plugging in the AC on the 4 port one, this will give full power to every port which it cannot do normally.

bradavon · Post by **bradavon** » 16 Jan 2007, 18:33

Lourdes wrote:USB can supply 500mA in 100mA increments, with a hub this is 400mA because the hub needs some. Some devices need 500mA alone so they can't be run from a hub.

It's misleading to state on all the package categorically no AC adapter is needed (yet include a connection anyway).

Lourdes wrote:I'm not sure why you're having problems. It may be that the hubs are designed for less pwoer or a USB bus issue. I'd try plugging in the AC on the 4 port one, this will give full power to every port which it cannot do normally.

I don't think it's a bus issue as plugged directly into the usb ports (any of them) all the devices work fine.

I'd like to do that but it's a tiny connection for starters so I don't know what type of adapter to use and secondly nowhere on the Hub or packaging does it say what voltage it needs, which is really unhelpful. The monitor was expensive but the USB Hub is a cheapo from eBay. You get what you pay for I guess.

I'm more concerned for when I get a laptop I'm going to have to have some type of hub as I will need 7 or 8 USB ports and as most laptops only have up to 4 it won't be enough. I'd put a PCI Card into a desktop pc but obviously I can't do this for a laptop.

I think I'll just get a proper powered hub when I buy a laptop. It is annoying though that two hubs have now struggled, it makes them frankly useless.

Thanks btw.