I've got a cheap old laptop and a cheap new Android phone and a cheap unpowered USB 2.0 hub I just bought.

A few minutes ago I noticed that connecting the phone to the laptop via the hub, while recognized by both devices as charging, does not actually charge the phone battery. In fact the charge was slowly going down as I was using it. (Yes the laptop is connected to AC.)

Before I got the hub I regularly charged the phone from the laptop directly and it was fine.

I bought the hub since my laptop's keyboard is going bad so one USB port is taken up by the cheap USB keyboard. But it worked great with the keyboard, a mouse, and the phone connected to transfer files, all at once.

Is it normal behaviour that connected devices would work but charging wouldn't? Or is this just a sign that the hub is a cheapie?

I'm just asking out of interest really. The situation is not dire (-:

  • 2
    Is the hub externally powered or is it powered by the computer only? – Mokubai Mar 17 at 6:33
  • Oh I meant to include that it's not a powered hub. So yeah just from the computer. – hippietrail Mar 17 at 6:34

For an unpowered USB hub this is indeed normal.

The USB specification allows for power negotiation. What this means is that by default only a small amount of power is available, enough for a USB memory stick or keyboard or mouse, but not enough to power a hard drive or phone.

During connection the slave device (phone) can negotiate for more power if it is available. For powered hubs this is not usually a problem and the full power is available for all ports so the port simply supplies more current. In a powered hub the full current may be available without negotiation.

In an unpowered hub the current to the hub is limited by the USB port on the computer. As such that current must be managed so that all the ports on the hub get an equal share of the supply so that all port simply just work.

As a result unpowered hubs will not supply enough current to any given port to charge a phone or power an HDD. Flash sticks and keyboards will work, as will a self-powered device like your phone, as there is enough power for them but they will be limited to low power.

Your laptop ports are effectively full powered ports, but your USB hub is limited.

Many USB hubs, even cheap ones, do actually have a power input to allow them to be used as powered hubs which would enable full power for each port.

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