[mythtv-users] [Slightly OT] solar power for all our gadgets

Michael T. Dean mtdean at thirdcontact.com
Mon Mar 9 20:59:27 UTC 2009

On 03/09/2009 04:15 PM, Stackpole, Chris wrote:

>  From: Michael T. Dean
> > Also, newegg has a search criterion for PSU's that allows you to
> > specify 80 PLUS (as the link above does) as well as 80 PLUS Bronze
> > and Silver (they don't currently carry any Gold PSU's).  Go to
> > 
> >  and select an option for Energy-Efficient.  Note that 80 PLUS
> > guarantees 80% or higher efficiency over a range of loads from
> > 20-100% (and is /vastly/ different from the "up to 80%"
> > efficiencies listed in newegg specs for non-certified PSU's).  The
> > Bronze/Silver/Gold certifications add to the 80 PLUS certification
> > specific minimum efficiencies at 20%, 50%, and 100% loads.  Bronze
> > is 82%/85%/82%.  Silver is 85%/88%/85%. Gold is 87%/90%/87%.  Note,
> > however, that many of the 80 PLUS standard PSU's are /very/ close
> > to the same efficiencies as the Bronze-certified PSU's.  See the
> > PSU reports for details: http://80plus.org/manu/psu/psu_join.aspx .
>  I have just started researching this and this seems like a good
>  conversation to jump into. Hope no one minds me asking a few
>  questions. :)
>  I have been looking to replace my ancient P4 Myth frontend and its +4
>  yr old PSU with something like an Intel Atom w/ Nvidia and VDAPU (I
>  also have a number of other systems that have high uptimes that I am
>  trying to replace as well). I am hoping to cut these really old
>  systems in favor of ones that are much more efficient. It has been
>  suggested to me to look at the Silver 80 PLUS PSU's but the smallest
>  wattage I have seen on the Silvers is a 700W. Way more then an Atom
>  needs. However, it is my understanding that if a system draws (for
>  example) 200W then there is no difference in power wasted for a 300W
>  vs a 700W.

Basically...  The PSU will not draw 700W unless 700W is requested (and, 
really, it's very unlikely that you could actually get it to draw 700W 
as that 700W is spread out over many different "rails" providing power 
at different voltages, so you'd have to have the exact right combination 
of hardware that maxes out all the rails, which won't happen).

>  In fact, if I understand correctly, a 300W at 75% load
>  pulling 85% efficiency is worse then a 700W at 35% load pulling in a 87%
>  efficiency. Correct? Or have I completely misunderstood what I have
>  gathered so far?

I think so, if I understood what you're saying.  It's the efficiency at 
the particular load that you need to be concerned with.  So, if your 
"real" power usage (i.e. the amount of power consumed by the hardware) 
as opposed to the "wall draw" is 200W, then with an 85% efficiency, your 
wall draw would be 235.3W (200W / 0.85 W/W) and at 87% efficiency would 
be 229.9W.  Note that extra 5.4W draw would require 184.9 hours of 
runtime to equal 1kWh, so paying for the 87% efficiency would save you 
1kWh/week (actually per 7 days 16 hours).  Even at $0.44/kWh, that would 
take quite a while to pay off the cost difference (420.2hrs/$1 = 
17.5days/$1).  If you have a more reasonable $0.15/kWh, it's more like 
924.5hrs/$1 (=38.5days/$1).  (And this is assuming a load of 200W--which 
is likely overstated for the real world--see below.)

Note, though, that if an 80 PLUS standard PSU at 50% load may well be 
more efficient than an 80 PLUS Bronze PSU at 20% load.  For example, 
given a real power usage of 200W, a 400W PSU would be working at 50% 
load and a 1000W PSU wuold be working at 20% load.  The Bronze 
guarantees 82% efficiency at 20% load (and only guarantees 85% at 50% 
load), but many of the standard PSU's operate at about 84.x% efficiency 
at 50% load.  So, it's possible that you may actually get better 
efficiency from a smaller, standard (non-Silver or non-Bronze) PSU.  See 
the PSU charts at http://80plus.org/manu/psu/psu_join.aspx for specific 

And, lastly, as I mentioned in my post with actual 
measurements/calculations/comparisons ( 
http://www.gossamer-threads.com/lists/mythtv/users/371460#371460 ), my 
master backend has a /lot/ more non-energy efficient hardware than 
you're talking about:

Mother board: PC Chips M848A v3.0 (SiS746FX NB & SiS963L SB)
Processor: Athlon XP 2400+ (Seems to be about 65W or 70W TDP)
HDD's: 2x1.5TB HDD, 1x750GB HDD
Video: 1xNVIDIA GeForce FX 5200 (discrete)
Audio: Realtek ALC655 (integrated)
Capture Cards: 2xpcHDTV HD-3000's
Other: 1xRosewill SATA/IDE card

and yet the wall draw was:

Without SETI at home--i.e. mostly idle:
  130.26W (new PSU)
  151.56W (old PSU

With SETI at home--i.e. CPU at max (with a lot of interrupts):
  148.26W (new PSU)
  169.14W (old PSU)

So your system shouldn't draw anywhere near 200W (meaning that you could 
even be /below/ the 20% load--therefore, possibly below 80% efficiency, 
even--if you get a "large" PSU that's Silver rated).

>  It also appears to me (from my limited research so far) that the
>  price difference between the 80 PLUS certification and the
>  bronze/silver/gold doesn't justify the purchase. It seems to me to be
>  more of a bragging point because the difference of ~3% power savings
>  won't come close to covering the price difference even after several
>  years. Am I wrong? I think that was what you were saying up there,
>  but I might have misinterpreted you to fit my conclusion so I just
>  wanted to verify. :P

All mine are 80 PLUS standard as--especially with my electricity prices 
at just over $0.10/kWh--the cost difference is /not/ worth it.


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