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I have recently bought Lenovo Enhanced keyboard for my x200s and Ultrabay setup. The main reason was to get two additional USB ports. The problem I have is that there's not enough power for anything plugged in those ports. I get messages of failed device installs and USB high-speed device being plugged to USB 1.0 port.

I have looked at Device Manager to see the amount of current that goes to the keyboard (and it's USB hub) and it's about 100mA, that is clearly not enough to power USB 2.0 web cam or memory stick.

My question - is it possible to change the amount of mA that is allocated to a particular USB hub in Windows 7?

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3 Answers

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It happens automatically, there's nothing special you need to do. When the operating system detects a new device on a hub downlink port, it will put the device in a low-power configuration mode and read its power profiles. It will then see how much spare power is available to the hub and choose the highest power profile it can support with the available power.

The computer can only supply so much power on each of its ports. The software already does the best job it can to supply needed power to as many downstream devices as possible.

It sounds like the keyboard's built-in hub is a USB 1.1 hub though. So you'll never be happy connecting USB 2.0 devices to it.

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Thanks for explanation, David. What I was after though, was whether you can specify the amount of power allocated to a given USB hub. – Taavi Oct 26 '11 at 21:29
The system will give as much as it can to every USB port it has. To my knowledge, no device other than a hub apportions power between its ports. Every endpoint device has only a per-port limit, not a total power limit. – David Schwartz Oct 26 '11 at 21:30
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No, but usually there is a round power port on every USB hub, so you can connect an external power supply. Those are always 5volts, and usually 500mA or 1A. They're usually fairly cheap.

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I'm afraid David's correct, there's no mention on the Lenovo site (http://shop.lenovo.com/us/itemdetails/73P2620/38/C39222A11DEF47F490A58490A545DAC0) about USB2 or an external power adaptor for the keyboard's USB hub :(

Like linkxs suggested - look for a connection on the keyboard you can connect a power supply to...

Failing that you'd have to buy an additional USB2 hub for your 2.0 devices.

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Looking at the specs again, it says "Two built-in USB 2.0 Full Speed ports for additional desktop expansion" implies it to ooze enough power to satisfy USB 2.0 devices. What @linkxs had in mind was an external USB hub, I guess. The keyboard does not have any such option. – Taavi Oct 26 '11 at 21:28

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