[time-nuts] Modern motherboard with RS232 port

Hal Murray hmurray at megapathdsl.net
Sun Aug 19 15:59:08 EDT 2012


ed_palmer at sasktel.net said:
> You have to measure the power draw and you have to  measure it in volt-amps,
> not watts because that's how residential power  is measured (at least in
> North America). 

Are you sure about that?  I've never seen that claim before.

Here is PG&E's blurb that covers their residential rates:
  http://www.pge.com/tariffs/tm2/pdf/ELEC_RULES_2.pdf
I didn't find a section that says "we bill by watts not VA".  I did find a 
section that discusses tariffs based on horsepower vs watts and it mentioned 
volt-amps.  They clearly know about the difference.

My bill says Kwh not Kvah.


actast at hotmail.com said:
> I may not have had enough coffee yet, but if Volt X Amps = Watts why would
> there be a difference? 

The magic word is power factor.  In AC, the power is volts*amps*cos(angle).
  http://en.wikipedia.org/wiki/Power_factor

Consider an inductor.  The voltage and current are 90 degrees out of phase.  
Half the time, one of them has the wrong sign.  Sometimes you are putting 
energy into the magnetic field.  Sometimes the field is putting power back 
into the line.


-- 
These are my opinions.  I hate spam.







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