[mythtv-users] Power supply for ATX

Brian Wood beww at beww.org
Thu Jan 25 22:10:05 UTC 2007

On Jan 25, 2007, at 12:44 PM, Jarod Wilson wrote:

> Yep, 600W supplies in general are stupid. Who actually needs that much
> for a home system? Unless you have an SLI setup, quad dual-core chips,
> and 8 hard drives in your system, I fail to see how you'd need 600W.
> Hell, I have a box with an AGP card, 4 PCI cards, dual CPUs and 12
> drives in it (my master backend) that has only a 500W supply, and its
> been rock solid for the entire year and a half its existed. My  
> frontend
> box (an Athlon 64 3500) has a mere 330W supply.

My main Linux box has an AMD FX-60 CPU running flat out (No PowerNow  
or other speed reduction) and 4 drives. My Kill-a-Watt shows it is  
only drawing about 120 watts, or 180 VA at idle, and goes up to  
perhaps 175 watts during very CPU intensive activity. It has a single  
7600 video card, and that CPU is considered a power hog.

You're correct that a couple of 6800s in SLI would significantly  
increase that, but certainly not anywhere close to 600 watts. It's  
not like an audio amp where running far below the rated power can  
give you lower distortion (though perhaps higher noise). In fact  
running a PAS way below rated output might even result in reduced  

A certain amount of the problem is certainly "my PS is bigger than  
yours" among gamers, and manufacturers literature trying to sell more  
expensive units to people with more money than sense.

The quality of the DC power delivered is more important IMHO than the  
sheer quantity. Ripple, regulation and other factors matter a lot  
more than pure wattage in many cases.

But the sad fact is that the power supply in a modern PC is a very  
neglected part of the system and one of the first places where  
manufacturers look to save money because most consumers look at CPU  
and drive numbers and are not willing to pay more for a quality PS  
even if they understood the facts.

You can sell something for more money if it gives you bigger  
"numbers" to brag about, but not if it only gives you a more  
reliable, quality unit.

> I've become quite partial to supplies that 1) carry 80plus  
> certification
> (>80% efficiency) and 2) rate highly in silentpcreview.com's noise and
> quality testing.

The power factor and efficiency ratings are important, especially  
with a Myth machine that is on 24/7. It was pointed out here recently  
that a full-time machine can cost more than $20/month to run in some  
parts of California.

The power factor's importance depends on several things. Most  
residential service in the US is based on wattage and assumes a 1.0  
PF. This is for several reasons, including the fact that the  
utilities don't want to put expensive meters into every house.

OTOH if you are in a commercial setting you might well be billed for  
"apparent" and not "real" power consumed, and you might have some  
sort of demand pricing as well. A higher cost PS that makes sense if  
you have 50 machines in an office setting might not make sense if you  
have one box in a home.

Noise may or may not be a factor to you, depending on whether the  
machine is in a closet in your basement or in your living room. High- 
quality fans cost more than cheap sleeve-bearing types but they  
certainly last longer. I really hate replacing fans :-)

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