[NBLUG/talk] Do I need a bigger power supply?

Lincoln Peters sampln at sbcglobal.net
Wed Jul 28 21:48:20 PDT 2004


On Wed, 2004-07-28 at 14:04, scottmc at sonic.net wrote:
> Does your ampmeter have a min/max feature?  Try capturing the peeks, which
> would happen at power up and probably after a soft reboot too, where the 4
> HDDs get scanned.  SCSI server systems typcially have a firmware option to
> power up the drives in order instead of all at once.  Smaller power
> supplies will have issues with this many drives coming up at the same
> time.  Also the 300W is usually at 25C, but typical temps around the PS
> can be as high as 40C, where a cheaper PS will can then drop down to
> 210W-250W.

I'll have to shut down in order to re-connect the ampmeter, but it
sounds like I should check for min's/max's.  The ampmeter doesn't have a
min/max feature, but I can probably tell the initial current flow by
closely watching the meter when I turn on the computer (it's an analog
display).

I know that watts equals amps times volts, so if a 300W power supply was
fully-loaded, it would draw approximately 2.5 amps.  I'm also aware
that, when the computer turns on, there will often be an initial surge
in current (as the motors get started) approximately equal to 6 times
its normal current usage.  Of course, the power supply is supposed to be
able to handle a surge like that if it doesn't last too long.

On the other hand, it is likely that, once the system has been running
for a few minutes, the internal temperature would rise to almost 40C,
thus reducing the power supply's efficiency as you describe.  This would
explain why the hard drives only fail when I do a warm reboot (they must
be momentarily spinning down, but when the power supply is not given a
chance to cool down it cannot provide the necessary power to spin them
back up).  It sounds like either a bigger power supply or a
better-cooled power supply (or both) is called for.

I've stripped a 600-watt power supply out of a testing box in my garage
and I plan to put it in this computer.  I'll report back after I find
out if the 600-watt power supply solves the problem (I'll also measure
the amperage, both with the old power supply and the new one).  And,
yes, I am sure that this 600-watt power supply is in good condition.

---
Lincoln Peters
<sampln at sbcglobal.net>

"Well, social relevance is a schtick, like mysteries, social relevance, 
science fiction..."
-- Art Spiegelman





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