[mythtv-users] Power Measurement (Was Architecture Idea - Raspberry Pi, VM, XBMC)

[Boleslaw Ciesielski]

On 01/14/2013 10:49 PM, tortise wrote:
> Hmmm time to chip in with my farthing.  As best I can tell accurate
> mains power measurement for switched mode power supplies is at best a
> challenge. The problem is that these do not have a power factor of 1, so
> simple power measuring devices get it wrong as they incorrectly assume a
> purely resistive load.  As Kill a watts were silent on this when I last
> looked I assume they accurately measure a resistive load e.g. an
> incandescent light bulb, however may well be quite inaccurate for fancy
> electronic kit.  An example CCF light bulb I have here has a power
> factor of 0.9.  Who knows what the switched mode power supplies are, and
> beyond that I expect it will change depending on the load....

First off, these days any self-respecting PSU will have power factor 
correction circuit which brings it very close to 1.0 (like 0.99).

Second, Kill-a-Watt can measure and display power factor, so one would 
think that it can also adjust for it :-)

So I do not believe that PF by itself is the cause of the inaccuracy.

Bolek