Date: Sat, 20 Mar 2004 17:46:22 +0800 From: Raymond <[EMAIL PROTECTED]> Subject: Re: [LIB] USB powered external HD
Well my experience in getting 2.5" USB HDDs working with my libretto have been documented in the recent past in this list but the crux of it seemed to come down to not only power but power stability. The power to the USB ports on the PCMCIA card that I have don't appear to be as well regulated as say the port on the EPR. I suspect what is happening is the USB device is being a little misbehaved and suddenly switching on the hard drive in a way that the USB port doesn't like. This causes the voltage on the USB port to dip momentarily - hardly enough to even show up on a digital ammeter but enough to reset either the USB port or the USB HDD controller. As it resets, it turns the hard drive off then back on again, causes a power dip and the process repeats ad infinitum.
Beyond power though there was another weird thing I had happen - even when I jumped a separate power supply into the 2.5" hdd, I still got problems, albeit slightly different ones. I've been able to run other things like 3.5" hdds (using external power supplies) and even a DVD burner, off the same 2.5" HDD 'case' electronics (through a converter cable) and they've been fine ...
Of course, whilst the ports on desktops are rated at 500mA, you can in fact draw a lot more ... I've used a 750mA hard disk in my USB2.0 HDD case and it seemed rock solid, even when plugged into my libretto's EPR USB port. It does hiccup a bit though when I plug it into my desktop USB2.0 ports through a 1m USB2.0 extension cable when there are other devices on the same root hub (I'm guessing the drive is running the ports close to their limits and the drop over the cable is enough to kill it).
- Raymond
At 10:59 PM 19/03/2004 -0800, you wrote:
Date: Sat, 20 Mar 2004 07:58:43 +0100 From: "Wouter Smith" <[EMAIL PROTECTED]> Subject: Re: [LIB] USB powered external HD
But this is not a limitation of the Libretto. According to USB specifications a USB-port should give 500mha (or less). Even my 6 build in USB2.0 port in the desktop can only give 500mha.
So if it is true spinning up a 2.5" hd takes about 1000mha, not a single USB-port in the world should be able to power it and they should ALWAYS require a power-adapter of some sort. That means all external HD producers are lying when they say it usually does not require external power (ok, wouldn't be the first time but seems unlikely).
Or am I missing something? I've read some posts on the http://www.everythingusb.com/ and there you also hear quite some stories of people requiring external power...
Hmmm... so the only way to find out is to actually test it before purchase!
And how about those 1.8" HD's?? Like the Archos ARCdisk? Do they require less power to spin?
Thanks guys for all your thoughts!
Regards, Wouter
----- Original Message ----- From: "Tory" <[EMAIL PROTECTED]> To: "Libretto" <[EMAIL PROTECTED]> Sent: Saturday, March 20, 2004 7:05 AM Subject: RE: [LIB] USB powered external HD
> Date: Fri, 19 Mar 2004 23:04:35 -0700 > From: "Tory" <[EMAIL PROTECTED]> > Subject: RE: [LIB] USB powered external HD > > > Hmmm.... what about Firewire cards? Do they also require an external > > power > > cable? > > > > Matt > > The limitation is not what kind of card you plug in the Libretto. It is > how much power the Libretto can give the card. The card can only get > 500ma from the Libretto, so, assuming it uses absolutely no power > itself, it can only pass 500ma through to your HD - not enough to spin > up the HD in 99% of all cases. > > Tory > > > > > ************************************************************** > http://libretto.basiclink.com - Libretto mailing list > http://www.silverace.com/libretto/ - Archives > > -------TO UNSUBSCRIBE------- > Reply to any of the list messages. The reply mail should be > addressed to: [EMAIL PROTECTED] - Then replace any text > on the message's subject line: cmd:unsubscribe > --------TO UNSUBSCRIBE DIGEST------ > Do above but with this on subject line: cmd:unsubscribe digest > ************************************************************** > >
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