true power consumption (was: disadvantages of linux cluster)

Peter Kjellström cap at nsc.liu.se
Mon Nov 11 05:09:39 EST 2002


On Fri, 8 Nov 2002, Dave Lane wrote:

[snip]
> technique is inline (I made a custom cable to do this) with both normal 
> (Fluke 73UIII) and true-rms (Fluke 79III) multimeters.
> 
>                  Unloaded (A)    Loaded (A)      Unloaded (W)    Loaded 
> (W)
> Normal          0.65A           0.74A           78W             88.8W
> True RMS        1.13A           1.3A            135W            156W
> 
> Note that huge difference in readings. This even surprised me and I should 
> have known better before trying this! I was also surprised how little 
> difference there was between loaded and unloaded. Note that the same 
> current readings were measured for unloaded when the machine was sitting in 
> the setup screen of the bios.

Hi Dave,

Thanks for the 'true RMS' rumbers, I knew my readings would be lower 
then reality but 1) I only wanted to illustrate the difference (and I hope
that still holds resonably well) 2) I had never expected such a
difference... That a true RMS instrument differs almost 100% is quite
remarkable.

/Peter

> 
> Note that these readings don't account for the power factor that others 
> have mentioned.
> 
> ... Dave
> Saint Mary's University
> Electronics Technologist turned Solaris admin turning Linux admin
> 
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  Peter Kjellström               | E-mail: cap at nsc.liu.se
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