Bytecc 2.5" External Drive Enclosure - bus power supplies enough juice?

[Madison Kelly]

Daniel Armstrong wrote:
> On 3/8/06, Madison Kelly <linux-5ZoueyuiTZhBDgjK7y7TUQ at public.gmane.org> wrote:
>> Daniel Armstrong wrote:
>>> Are these external drive enclosures that draw power from the USB ports
>>> getting enough juice to run properly?
>>>
>>> I am interested in combining a 60GB laptop drive with the Bytecc
>>> HD1-U2 2.5" USB2.0 Aluminum HDD Enclosure:
>>>
>> IIRC, Bytecc use a horrible chip which often locks up hard when you
>> start a transfer of any decent size. I can't think of the chipset off
>> the top of my head though, sorry. My personal opinion is to stay *far*
>> away from Bytecc... they're cheap for a reason.
>>
>> On the other hand, I have had good luck with Vantec's line, though I
>> have only used their 3.5" carriers. Generally speaking though; any
>> carrier that draws power from the USB bus will need ~500mA which is more
>> than the spec allows (350mA/channel). To get around this they generally
>> give you a USB pass-through cable that provides extra power for the
>> drive. These pass-throughs should only be put in between low-power or
>> self-powered USB devices (ie: a mouse).
>>
>> The real test is to look at the power draw on the hard drive you want to
>> use and add ~20/30mA for the controller. Then see if one or two ports
>> will provide enough power for you.
> 
> Thanks for the feedback Madison.
> 
> Considering your tip about Vantec, I checked out the Vantec NexStar3
> NST-260U2, a 2.5" external drive enclosure that connects to 2 USB
> ports for power.
> 
> The laptop drive I want to make use of is a 60GB Hitachi DK23FB-60. I
> found a pdf of the drive specifications online. It states that during
> seek/read/write operations it requires power in a range of 400-450mA,
> but I see that at initial startup the drive draws 900mA of power.
> 
> I am not familiar with electrical terms, but looking around online -
> if I understand correctly - it appears a USB device can draw 500mA
> from each USB port. Connecting to 2 USB ports should supply 1000mA and
> be enough power to spin up this drive and the controller?

   Are you on a laptop? After my last email I got to thinking and 
remember that yes, indeed, Lennart was right and that the USB2.0 specs 
calls for 500mA/channel. My laptop's PCMCIA USB2.0 adapter though only 
provided up 350mA from the PCMCIA bus and needed an external power brick 
to step the two channels up to 500mA/each. If you have a laptop, verify 
it's ability to provide the full 500mA.

   As for the rest, yes, two channels at 500mA each will be able to 
(just) handle the in-rush current (the high power draw needed when the 
drive spins up). Keep in mind though that you need to take the 500mA and 
*subtract* the power being drawn by any other device on the channel. 
Given the high in-rush current I would make it a point to have a 
dedicated secondary channel for the extra power (don't use it for 
anything else) and you should be good to go.

Madison

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