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

Mon Mar 9 21:23:33 UTC 2009

> From: mythtv-users-bounces at mythtv.org [mailto:mythtv-users-
> bounces at mythtv.org] On Behalf Of Michael T. Dean
> Sent: Monday, March 09, 2009 3:59 PM
> Subject: Re: [mythtv-users] [Slightly OT] solar power for all our
gadgets
> 
> 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
> > >
>
http://www.newegg.com/Store/SubCategory.aspx?SubCategory=58&name=Power-
> Supplies
> > >  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
> examples.
> 
> 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)
> RAM: 1GB
> 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.
> 
> Mike

Thanks for the info! It has helped me understand what I am buying a lot
more. :-)

As for the 200W, that was just a number I threw out there. From what I
am seeing on Newegg, some of these VIA and Atom processor/motherboard
combos pull considerably less then 50W. Once I add in a decent video
card, memory, and a flash drive* I am hoping to not top 50W under full
load.

*Thinking about compact flash as the primary storage, but I might just
use a standard USB 2.0 stick. For a basic frontend, it should do rather
well.

Thanks again for the info!
~Stack~