[K12OSN] electricity use

Robert Arkiletian robark at gmail.com
Wed Mar 14 04:09:44 UTC 2007

On 3/13/07, Vince Callaway <vince at totalsense.com> wrote:
> On Tue, 2007-03-13 at 19:50 -0700, Robert Arkiletian wrote:
> > I am not an electrician but I do teach basic electric circuits in
> > physics. The basic equation for power is P=IV (Power=VoltagexCurrent)
> This is why things get confusing.  Power supplies in computers are rated
> by the DC side of the power supply.

Good point! I didn't consider this. So the efficiency of the PS unit
is a factor. Nothing is 100% efficient.  I think if my memory serves
me right Europe has a law which requires a certain kind of more
efficient PS than here in North America. I can't remember the
technical details.

> The power supply on my workbench is rated at 150 watts.  Here is the
> real data from the sticker on the side:
> AC Input: 110v 3A
> DC Output: +3.3v 9.5A
>            +5V 10A
>            +12V 7A
>            +5V 1A
>            -12V .2A
> Max +5V + 3.3V = 123W Combined
> Max Total Output = 150W
> So as you can see it can potentially pull a lot more than the 150W
> rating implies.  A supply rated at 330W can actually pull up to 5 amps.
> It all depends on how much hardware is in the box.
> A diskless client should have as small of a power supply you can find.
> Bigger supplies will have more parasitic loss (heat).
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Robert Arkiletian
Eric Hamber Secondary, Vancouver, Canada
Fl_TeacherTool http://www3.telus.net/public/robark/Fl_TeacherTool/
C++ GUI tutorial http://www3.telus.net/public/robark/

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