powered usb hubs - max output?

martyp

Hi all,
I'm trying to find a means of attaching 3 usb devices to a laptop with just one usb port. This of course would mean either a USB hub or carbus USB adaptor.
Going with the USB hub route...
I have two powered USB hubs, one with a 600mA power adaptor, the other with a 2.1A power adaptor. Both have 4 ports.
What would be the power output of each of the ports on the hubs?

I'm thinking that without the power it'd be:
100mA for the hub, then 100mA on each port

With the 600mA adaptor:
100mA for the hub and 125mA for each port or 225mA?

With the 2.1A adaptor would I get 500mA on each port on the USB hub?

That's the plan anyway as the 3 devices being used use up to 500mA each, I need to be sure the hub can accommodate this?

Can I tell the individual power output of each port on the USB hub easily in XP Device manager? Would I just have to check every USB port and check it has 500mA on each one?

I'm worried that one item was damaged by insufficient amperage on the USB port on a non-powered hub...

Many thanks

fwor

The USB 2.0 standard permits a high-powered device to take a max of 500mA on each port.

From that you can deduce that the one with a 600mA power supply is not designed to handle more than one high-powered device at a time.

So you should use the hub with the 2.1A power supply.

You should not need to worry that a device has been damaged by being connected to a non-powered hub. It is very rare for anything to be damaged through receiving too little current.

bonzer

I'd probably guess the same, the 2.1A supply would give you the full 500mA on each port.

On the smaller one, I probably wouldn't bank on getting 500mA on any port. In theory it should allow a minimum 100mA per port, therefore if one port takes all the power it can't really supply the other three at all. Power in USB generally goes in 100mA steps, therefore 100mA per port seems more likely. However who knows what it does in practice.

I think the power supply capability of the hub should in theory be software readable, but I'm not sure where to look in Windows.

martyp

Many thanks both, I've used the 2.1A powered hub and it's currently supporting two 224mA devices and one 500mA one successfully and it shows as such in device manager power tab for the usb hub so it seems to be fine.

John_Gray

The figures for mA shown in Device Manager are the rated values - unless you actually measure the current drawn by the USB device from the port (and check the voltage), there's no way of knowing just how accurate the rated figure is. (And no, it isn't easy.)