USB 2.0 powered hub failure

[Lennart Sorensen]

On Mon, Mar 19, 2007 at 01:42:00PM -0400, Duncan MacGregor wrote:
> USB 2.0 hubs, it seems, may have power supplies that are too weak.
> 
> With pen drives and flash cards, a weak power supply manifests itself as  
> connections that are  inconsistently maintained and unreliably established. A 
> connected hard drive would sometimes only click.
> 
> Using a 5volt 2.5 amp power supply brought two of my hubs to life.
> The 1 amp or unmarked supplies were useless.
> 
> It looks as though you need a power supply that provides half an amp for each 
> connection on the hub

Well USB allows 100mA per port until the device connects and tells the
system how much power it needs, up to 500mA.  Some external HDs use two
usb connections to get up to 1A of power.  So a usb hub with a 1A power
supply can only actually handle 2 ports at full allowed power (assuming
the hub itself requires no power at all).

So the 1A adapter seems like a bad design choice.

--
Len Sorensen
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