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I bought a cheap Hub for powering my 5 arduino(s). It has an AC wall power adapter. Can i determine if it actually powers my USB devices and what amount of current per USB port can deliver?

The USB hub has one LED, that lights when i power it with the AC adapter, and until now everything works ok.

In the control Panel, in the USB ports i can't find any useful information. I can see the Hub as port 4 hub 3, but says power required "unknown".

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  • \$\begingroup\$ The design of the USB hubs varies as a function of their cheapness. If you could open the hub and post the photo of the PCB (both sides), that would help us give you a more accurate answer. \$\endgroup\$ Aug 12 '16 at 17:37
  • \$\begingroup\$ It works fine and it costs around 3.79 euro for 7 ports. It really powers the devices, as i found after i unplugged the USB. Not only this but previously I had a glitch with my Due when i connected it to my laptop's USB ports, crashing on startup. Guess what. When i plug it in the "cheap" hub it works fine... :-) \$\endgroup\$
    – John Am
    Aug 12 '16 at 18:10
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The simplest way to know if your hub is providing power to the ports or not is to just plug something into it while it's not connected to the computer. If it gets power then the only place it can possibly be getting it from is the hub's power supply.

How much current it can deliver depends very much on how they have designed the hub. Many cheap hubs just have a direct connection between the power supply and the power pins of the ports. The only limit then is what the power supply can provide (less what the hub itself needs to operate).

Better ones include power control and over-current sensing, etc. In these cases, if they are to adhere to the USB 2.0 specs, then 500mA is the minimum current they should be able to provide whilst self-powered, or 100mA when bus powered. Any more than that and, at the hub's discretion, the power may be shut off.

Of course, the hub is free to provide considerably more current, in which case it can be classed as a CDP - Charging Downstream Port - which can be used to charge high capacity battery systems like mobile phones, etc, where they request (or expect) much higher currents than the USB 2.0 spec allows for a standard port.

So the only real way of knowing just what your hub can do is to pull it apart and see what kind of power circuitry is connected to the power pins on the ports, and look at the datasheets for any chips involved.

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  • \$\begingroup\$ The rating marked on the power supply for the hub may also give a hint as to the maximum power available. \$\endgroup\$
    – Simon B
    Aug 12 '16 at 22:18

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