[geeks] Little Falls 2 System Power Consumpion Question

[Mark Benson]

On 14 Dec 2008, at 20:53, Micah R Ledbetter wrote:

> I don't remember the numbers off the top of my head, but doesn't USB  
> provide less than the maximum power that 2.5" IDE disks can suck?  
> IIRC 2.5" IDE disks can require up to 5.5v, according the its spec,  
> and USB doesn't have to provide more than 4.5v, according to its  
> spec (the numbers could be wrong, I can't remember very well). Some  
> laptop drives never thirst for their potential maximum power draw,  
> so there is never a problem, but some do.

As far as I was aware, USB is supposed to provide 5V at up to 500mA  
per port (may even be per bus). USB Mice use 100-150mA. A wireless USB  
Stick will suck most if not all of that 500mA. A USB 2.5" Hard drive  
can often require up to an Amp, hence why some 2.5" enclosures include  
a Y shaped 'double lead' for grabbing the extra power off a second  
port. To add to the pain-in-the-arse factor a lot of laptops under- 
power the USB ports, meaning you sometimes can't muster the power to  
even run a buss-powered drive. On some I've used this was the case on  
battery but not on mains, like the USB ports drop to low power mode.

> I ran into this problem once, where any time I had heavy read or  
> write access on an external bus-powered USB drive, it would fail and  
> the OS would see that the disk had been detached without first  
> ejecting it. I tried the drive in two different enclosures, and the  
> behavior persisted.

Yeh it sometimes has the alarming effect f making the drive head-bash.  
You fear the worst only to find it was just suffering low power.

> IIRC, Firewire provides a little bit more, and so I'm going to get a  
> bus-powered Firewire<->laptop IDE enclosure whenever I get around to  
> it.

Firewire 6-pin provides a higher voltage and more current, that's why  
Sony Developed iLink 4-pin - so they could put Firewire on laptops  
without them running the laptop's batteries down, as the 4-pin  
provides no power at all. I tend to use Firewire anyway where i can,  
because it's just better than USB 2.0, but I also have a few  
enclosures that don't have it.

-- 
Mark Benson

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