[iyonix-support] Re: USB ext hd & Fat32FS
- From: John Ballance <jwb@xxxxxxxxxx>
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Thu, 14 Apr 2011 00:25:41 +0100
On 13/04/2011 23:24, Ron wrote:
In message<Marcel-1.53-0413111039-c72pErr@xxxxxxxxxxxxxxxxxxxxxx>
Chris Evans<chris@xxxxxxxxxxxxxxx> wrote:
Another possibility is to use a USB powered hub - i.e. one with its
own mains supply. That might supply the necessary extra power, as it
sounds as though the drive exceeds the requirements allowed by the USB
spec.
Alternatively if there is a USB power only plug we do a USB Mains charger/PSU
http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=CAB-USBPOWER-BK
It outputs upto 1Amp!
This is still not addressing the point that a USB hard drive that
has no external power socket will most likely need the double
headed lead for the secondary power source or extra power from
two USB ports.
Even a powered hub may have a limit per port.
The confusing part is that some X86 machines break the rules
and do put out enough power on one port.
Ron M.
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The USB rules are quite simple.
A USB port must provide 1/2 amp if powered.. i.e. its in a box with
connected power supply.
If not so, i.e. it is a hub on the end of a USB lead, then if no power
supply on this hub, total available power is 1/2 amp for the hub and any
sockets on the hub.
IF the hub has a power supply, then it can source 1/2 amp at each USB
socket.
It is not unusual for external devices to need more than 1/2 amp. The
usual convention then is to have a power supply with this device.
Occasionally you'll see a bodge that perhaps feeds off 2 (or more) USB
sockets.
Incidentally the USB stack interrogates the usb device and will only
enable it if it reports as needing less power htan available on that USB
socket.
Hope that helps
John
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