Dodgy USB Hub?


8 posts
by MothBox » Tue Aug 07, 2012 8:55 am
I've got a little USB hub that seems to work okay for keyboard and mouse but when I plug a hard drive into it the PI (running Raspbian + XBMC) cannot register its existence. What's odd is that the drive keeps "reving", as if its spinning then not then spinning then not.

It works fine when this is all plugged into my laptop.

Does this sound like there is a problem with the hub (admittedly bought on the cheap) or is this a PI / OS problem?
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by Jim JKla » Tue Aug 07, 2012 8:58 am
Sounds like there's a power issue with the drive does the HD draw its powerfrom the USB. ?

It could be the power your feeding the Hub
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by MothBox » Tue Aug 07, 2012 9:02 am
I wondered this - if on the laptop the laptop is actually powering the HDD and on the PI its getting some power but not enough to power it up properly. It is a powered hub.

I'm tempted to just ditch it and get one which is a little more expensive (assuming more money = better quality) and trying again.
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by Jim JKla » Tue Aug 07, 2012 9:05 am
Look around look to get the best amp rating for your cash on the psu for the hub

Just out of curiosity are you running the RPi from the Hub or from a seperate psu.

I'm using an old Belkin F5U010 7 port hub it uses a beefy 6v 4Amp psu ;)

I am also powering the RPi from the hub and controlling the hub foom the RPi
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by MothBox » Tue Aug 07, 2012 9:09 am
RPi has a separate power supply, however, if I can I'll try and power the lot from the hub.
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by Jim JKla » Tue Aug 07, 2012 9:14 am
That then fits the pattern your RPi continues to run If the RPi was powered from the hub I would expect the Pi to fall over at the same time.

There is a risk you could corrupt your SD with power dropouts.
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by andyroyal » Tue Aug 07, 2012 9:54 am
Any idea how much current the hard drive draws? A keyboard or mouse will typically draw less than a current unit, which in USB 2.0 is 100mA, but the ports on a powered USB hub should be capable of supplying 500mA. That might not be enough for some hard drives. Are you using a Y-cable to plug the hard drive into two USB ports?
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by itimpi » Tue Aug 07, 2012 10:14 am
While some 2.5" HD drives claim to draw less than the 500mA offered by a standard USB port I always find that it is more reliable to use a 'Y' cable so that power can be drawn from two ports. The only time I do not bother with the 'Y" cable is if I am using a USB port rated as "High Power" (which are becoming commoner on recent PC/laptops).

A classic visible symptom of an underpowered 2.5" HD is a constant clicking sound as it keeps trying to spin up and fails.
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