Re: Power Failure when connecting HDD to VS 3100

From: Alexander Wessel (flexx_at_chello.at)
Date: 09/14/03 

Date: Sun, 14 Sep 2003 19:40:07 GMT

Michael Unger wrote on Sun, 14 Sep 2003 20:19:03 +0200 (<bk2c0k$nphro$1@ID-152801.news.uni-berlin.de>):
> On 2003-09-14 19:44, "Alexander Wessel" wrote:
>
> > [...]
> >
> > It's irrelevant whether the HDD is connected to the SCSI cable or not,
> > just be connecting the power cable the machine stumbles and dies.
> >
> > What's happening here? Is the HDD draining too much power from the PSU?
>
> Typically the built-in AC outlets of PC (and similar) power supplies are
> "low current only" (0.5A or less) and in many cases they are protected
> against excessive currents. A possible protection device is a resistor
> with a resistance depending on temperature and a positive temperature
> coefficient. So if the current is too high its temperature will rise
> enough (remember, P = R * I^2) to make it a high-resistance "fuse". Some
> of these devices have a very sharp increase in resistance above a
> specific temperature. When it cools down -- which typically takes some
> seconds -- it gets low-resistance again.

Yep, this seems to be what's happening. Since it works again after
letting it "cool down", it's certainly not a fibre fuse that's burt
trough (with gives me hope, since I'd really hate having to open that
PSU ;)

> Do you have any data regarding the *inrush* current of the HDD?

Umm.. No. I'm a (somewhat daring) software guy, who doesn't bother to
open up a case, and make a few connections, but that's about it... ;) My
knowledge of electronics is limited to what the hardware guys managed
squeeze into our more or less ignorant brains in school... ;)

However, it's a normal SCSI HDD (I closed the case now, but I think it
was a standard DEC (acually a Conner) HDD supplied with the system), so
it should "fit" the system. I guess it's not "normal", maybe something
is broken in the HDD electronics that causes too much current to be
drained from the PSU.

> Did you try to connect it to an independent wall outlet?

How would I do that? It's an internal drive, connected to a standard
4-wire (ATX-like) connector.

> > Or is the PSU defective?
>
> Not necessarily.
>

That's what I hope, since the HDD will be more easily to replace than
the PSU, I guess. 

-- 
Alexander Wessel
mailto:flexx@chello.at
http://www.flexx.at.tf

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