RE: [Thinkpad] Questions re: external HD enclosures (USB)

Hello,

PCMCIA can not supply the amount of power called for in the Firewire Spec.
Some Firewire and USB Cardbus Cards have a coaxial power jack so an external
power source can be used. Again usually a cable to the PS/2 port.

Also a 4-pin Firewire connector does not have power pins.

So we discovered another reason to have a PS/2 port on a laptop.

73 Eric

-----Original Message-----
From: thinkpad-bounces@stderr.org [mailto:thinkpad-bounces@stderr.org]On
Behalf Of Andrew Webber
Sent: Tuesday, December 21, 2004 10:48 PM
To: thinkpad@stderr.org
Subject: RE: [Thinkpad] Questions re: external HD enclosures (USB)

On Tue, 21 Dec 2004 12:32:53 -0500, Paul A. Pennington wrote:

>Spend a few bucks more and get a drive with a wall-wart power
>supply. Hard disks draw too much current to draw it from a
>notebook computer. Check on CyberGuys:
>
> www.cyberguys.com

On Tue, 21 Dec 2004 14:45:19 -0500, Cottrell, Eric wrote:

>I agree. The USB info I have seen indicates a 500mA power limit
>through the bus. Anything over that must be self-powered.
>2.5 Drive specs say around 520mA average(!) when operating and
>800mA to 1100mA maximum during startup.
>
>I suspect some drive enclosure makers get away with bus powered
>because some USB ports can provide more than 500mA of current.

Okay, thanks to you both. But I do see a lot of enclosures that
_aren't_ powered. I guess they're just taking a chance. Though
some do specify the PS2 for power, and some have a USB cable that
takes up two connections at the PC end (I guess that gives them
1000mA?).

It's too bad because I like the idea of not hauling around another
wall-wart that probably weighs more than the drive and almost as
much as my notebook!

>I have a nice combo USB 2.0/Firewire enclosure. It is only
>bus-powered on the Firewire side because Firewire is spec'd
>to provide 60 watts of power. There is a coaxial power jack
>and a power cable to a PS/2 pass-thru connector is included.
>If I did not have a PS/2 jack on the computer I would need a
>5 Volt regulated wall wart to plug into the coaxial power
>jack when using USB 2.0

This reminds me of my external DVD-RW, it requires power when
connected by USB and not when connected by Firewire. But I ran
into a problem with that which I never chased down.

I bought a PCMCIA Firewire card, of course it isn't thick enough
for a Firewire connector but rather than a dongle it has a Firewire
cable. The DVD burner doesn't power up when it's connected to
that. Is it possible the PCMCIA card doesn't provide the requisite
power? I don't have it handy (put it into a machine with only USB
1.1) but I do remember card's cable being less thick than the one
that came with the drive.

If it has to provide power to conform to the Firewire spec, I might
get it back and see if a (more expensive) Firewire HD enclosure
would do the trick for me.

Thanks!

andrew [awebber@wwwebbers.com]
ph 613-797-8123
fx 831-300-4097
------
For PGP public key, send email with "send public key" as subject

_______________________________________________
Thinkpad mailing list
Thinkpad@stderr.org
http://stderr.org/cgi-bin/mailman/listinfo/thinkpad
_______________________________________________
Thinkpad mailing list
Thinkpad@stderr.org
http://stderr.org/cgi-bin/mailman/listinfo/thinkpad
Received on Wed Dec 22 10:32:51 2004