Can I use an externally powered USB hub, solely as a charger?
I have a 'cheap' usb hub I picked up from amazon, and the other day while planning for holiday stuff such as charging devices, I realised this thing has 5 usb ports on it and is externally powered.
Could I just connect upto 5 phones/tablets to it, while it's 'powered on' and let them sit and charge?
Would it be dangerous or slow?
Would the number of devices charging effect how quickly they charge?
Do they need a 'host' device, before the charging will actually take place?
It is a USB 2.0 Hub, seen here
21 Answer
I wouldn't advise to use this hub as a charger. To begin, the manufacturer (or seller) is lying that it is "USB-IF certified". The description indicates that it has "5V 1A" AC-DC wall adapter, which cannot possibly feed all 7 ports, which would require at least a 4A adapter to comply with USB requirements,
Now, a high-end hub might have a special high-side power switches on each port, who provide current limits and overcurrent indication to host. But they are rare even in the expensive category of hubs. These switches usually are engaged only when the hub is connected to USB host and gets full enumeration.
However, cheap hubs use a "ganged mode", and tie power to all ports nearly directly to input external power. This kind of hubs have VBUS voltage out right after you plug the AC-DC adapter into a wall. In this case the 1A will be delivered to all 7 ports, and you will have 1 A total, which is only good for two USB ports.
More, since the hub is not marketed as "charging hub", all ports are likely the standard USB ports, and have no charging signature of any kind. Therefore most intelligent devices will see it as regular USB port, and won't take more than 500 mA, and likely will charge very slowly, if ever.
In summary, high chances are that this hub will source 5V on all ports without being connected to USB host, but it would't be able to charge more than two devices, and just at the standard slow 500 mA rate.
