[time-nuts] Thanks: Watts vs VA

Tom Knox actast at hotmail.com
Sun Aug 19 20:36:28 UTC 2012

Thanks for the responses. I did not mean to steer the thread off course. I understand all the theroy, I just didn't understand that VA automatically included PFC or crest factor where watts did not.
I would have assumed the opposite since watts is based on RMS.
Thomas Knox

> From: albertson.chris at gmail.com
> Date: Sun, 19 Aug 2012 13:16:08 -0700
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Modern motherboard with RS232 port
> On Sun, Aug 19, 2012 at 12:19 PM, Tom Knox <actast at hotmail.com> wrote:
> >
> > Hi Ed;
> > I may not have had enough coffee yet, but if Volt X Amps = Watts why would
> > there be a difference?
> That relationship holds for DC but with AC the phase relationship between
> voltage and current depends of the complex impedance of the load.    If the
> load is reactive the phase will not be exactly 90 degrees.  When we do the
> math inour heads most of us always simplify and don't bother with complex
> numbers but in real life impedance is complex.
> But for simple back of envelope calculations we can pretend the power is DC
> and just say Volt X Amps = Watts
> Another simple way to know if your PC is going to cost you an arm and a leg
> to run 24x7 is to place your hand over the cooling fan exhaust vent if hot
> air is coming out you can know for sure that you are paying $$$ to heat
> that air
> Even if the PC consumes only 50W that works out to 438 KWH per year at 20
> cents per KWH you can still pay for a new $100 Atom motherboard with the
> savings in power and see a profit 2 years.
> If gets worse in the summer if you need to run the AC.  Let's say the PC
> burns 1W.  That dumps 1W of heat into the building and if your air
> conditioning runs on a thermostat it will burn a little over 1W to remove
> the extra heat.  The AC is a multiplier of the power used in the house.
>  Using this logic someone at work figured out it was cost effective to
> trash very old CRT monitor in the building.   Same for the light bulbs, we
> pay a lot to cool the lighting load.
>   (I would have simply installed windows that open and saved even more
> money.)
> -- 
> Chris Albertson
> Redondo Beach, California
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