[mythtv-users] Re: Energy Usage of MythBoxes

Robert Denier denier at umr.edu
Mon Mar 21 03:41:03 UTC 2005


On Mon, 2005-03-21 at 13:21 +1000, David Whyte wrote:
> > Hrm... this
> > might be my excuse to get a PVR x50 card (~20/mo savings, payback in
> > 5-6 months... not too shabby).
> > 
> 
> Doesn't that just mean the card will consume the power to do its
> magic?  So where you save on the CPU you lose on the tuner.
> 
> Maybe...unless it takes less energy just to write the MPEG2!
> 
For people that are really determined to save power, you might want
to pick up a clamp on ammeter.  They run about $30 or $40 at hardware
stores.  You will also need an extension cord you can separate and get
one and only one of the power wires inside the clamp.  (All the
insulation should be left on the wires.)  Power = i^2 * R so basically
power utilization goes up as the square of the current.  For the actual
power usage multiply the amp reading by the RMS voltage.

I suspect thats about the only way to be sure if the PVR-250 will save
you any power usage overall.  Personally I rather doubt it will be
that much.

On another note.  I have no earthly clue what the power factor is for
computer power supplies, but one would think it would be possible to add
the correctly sized AC capacitors and correct that if you were really
concerned about it.  Of course then you need to do all the math and make
sure a nice case is found to keep the capacitor terminals away from
anyones fingers.  

Actually I don't remember if conventional electric meters will read a
larger value because of the tendency for the inductive loads to
outnumber the capacitive ones or not.  It might be something to check on
one day.



-- 
Robert Denier (denier at umr.edu)
PhD Electrical Engineering (May 2005)
University of Missouri-Rolla
http://www.finiteinfinity.com



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