[K12OSN] electricity use

[Doug Simpson]

In this discussion, we need to clear something up.

Just because a power supply in a computer says 300W does NOT mean that 
that is what it makes the comuter draw regardless.  That number is the 
maximum that that power supply is capable of delivering to the parts in 
the computer. Changing from a 300W to a 100 watt (if you can) won't 
change the draw of the computer much, if at all since the parts in the 
computer use what they use.

Think of it this way, you have a giant, MEGAWATT power supply connected 
to your house, but your house only *draws* a very small fraction of this 
power. The computer has a 300W (rated) power supply, but the components 
may only *draw* a total of 100W. The other 200W is not wasted. You are 
just using 1/3 of the *rated maximum* of that power supply.

Hope this clarifies this. . .

Doug

Robert Arkiletian wrote:

> On 3/13/07, Brad Thomas <bthomas at bhbl.org> wrote:
>
>> I am a social studies teacher and I've been building a lab in my 
>> classroom
>> of old, discarded computers over the last two years (I was up to 20). I
>> have been using small distros like DSL (DamnSmallLinux) to make them 
>> work,
>> but was planning to switch to a k12ltsp setup before the end of the 
>> year.
>> However, my principal just sent an e-mail last week instructing me to
>> remove all but 6 of the computers from my room implying that they were
>> using too much electricity. I just got back from a school planning 
>> council
>> meeting where she and an assistant principal said that they called Dell
>> (we buy all our new fat machines from Dell) and Dell said there should
>> only be one computer per 20 amp circuit (which translates into one per
>> room I think). As far as I can tell (using a Watts Up meter) one
>> computer-and-monitor use a little more than 1 amp of power, so I 
>> don't get
>> this. Can anyone out there give me some guidelines they go by? Or 
>> steer me
>
>
> I am not an electrician but I do teach basic electric circuits in
> physics. The basic equation for power is P=IV (Power=VoltagexCurrent)
> So 120 Volts (which is a north american standard) x 20 A of current
> equals 2400 Watts of power.  Now if you remember those old boxes
> probably have 200W power supplies max + monitor ~75W. Add another 25
> for safety. So I would say 300W/box is reasonable. Although less would
> probably work because I doubt they would draw the max of the PS unit.
> So with a 20A circuit (2400W) that equals 8 machines working at full
> tilt.
>
> Now compare that to an ebox 2300 + and a 19in lcd monitor consumes. 
> 15W + 40W
> Plus the server, don't forget.
>
>> to a good site? How much planning goes into ensuring proper electrical
>> flow into your k12ltsp labs?
>>
>> Brad
>>
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>
>