For quite some time people have been recommending high wattage / high quality psu's where they weren't required. I came across an article on Overclockers.com a while back where the author used a 380W psu in a mid/high-end rig and measured the psu and wall loads. As it turns out a member on the OC forums did the exact same thing and posted pictures of the process.
A C2D E6600 @ 3.4GHz, 975x mobo, 4x1GB DDR2, 8800GTX, 2 HDD, 1 DVDRW, 4x low power fans powered by an Antec EarthWatts 380
only draws 380W from the wall while under full burn-in and gaming load.
Therefore the psu is under a 320W load which in turn is an 84% load on
the psu. How often are you going to be under this kind of worst case
scenario load? Average load would be around 70%. According to JonnyGURU the EarthWatts is capable of 80% efficiency @ 20-100% loads. How long will this psu last? We already know that not all psu's are created equal, and there are
plenty of high end psu's that can sustain an 80-100% load 24/7 (yes,
that is continuous) as long as the temps are kept in range.
http://www.pcpower.com/technology/myths/
2. DON'T BE MISLED BY EXAGGERATED WATTAGE CLAIMS
To properly compare power supplies, wattage claims must
state the maximum ambient temperature for continuous,
full-load operation. Unfortunately for the consumer, this
information is usually withheld, opening the door for
manufacturers to exaggerate their wattage claims. They do
so by assuming an unrealistic ambient temp of only 25°C
(77°F), even though the actual internal power supply temp
is at least 40°C (104°F). Since the proper full-load
rating is 15°C higher for home use and 25°C higher for
industrial use, these power supplies produce 33%-50% less
power than their advertised ratings. See the derating
chart on the right.
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|
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Turbo-Cool 510 spec: full load @ 50°C.
"500W" Home PSU spec: full load @ 25°C, no load @ 70°C. |
As you can see it's important to choose a psu that offers continuous output @ 50C. The number of amps on the 12V rail(s) is also important. Some psu's claim to have multiple 12V rails but are in fact one single rail (preferred).
8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?
With all the hype about multiple 12-volt rails (ads claim that two
rails is better than one, five is better than four, etc.), you’d think
it was a better design. Unfortunately, it’s not!
Here
are the facts: A large, single 12-volt rail (without a 240VA limit) can
transfer 100% of the 12-volt output from the PSU to the computer, while
a multi-rail 12-volt design has distribution losses of up to 30% of the
power supply’s rating. Those losses occur because power literally gets
“trapped” on under-utilized rails. For example, if the 12-volt rail
that powers the CPU is rated for 17 amps and the CPU only uses 7A, the
remaining 10A is unusable, since it is isolated from the rest of the
system.
Since the maximum current from any one 12-volt
rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts =
20 amps), PCs with high-performance components that draw over 20 amps
from the same rail are subject to over-current shutdowns. With power
requirements for multiple processors and graphics cards continuing to
grow, the multiple-rail design, with its 240VA limit per rail, is
basically obsolete.
PC
Power and Cooling is once again leading the industry. All of our power
supplies now feature a large, single 12-volt rail. The design is
favored by major processor and graphics companies, complies with EPS12V
specs (the 240VA limit is not a requirement) and is approved by all major safety agencies such as UL and TUV.
- I decided to contact several reputable mfg's for their input.
_______________________________
-----Original Message-----
From: Enermax [mailto:sales@enermaxusa.com]
Sent: Monday, July 09, 2007 6:38 PM
To: elitekiller
Subject: [TSU-4450]: psu utilization questions
In this case our Infiniti power supply would be capable of handling 80% to 100% for any given number of time, and it can do it for 24/7.
So you can say that if you have a quality power supply, you can run up to 80% or 100% load and still be within the voltage specs. In the end you don't really need a bigger power supply then your system can use.
You can check the status or reply to this ticket online at http://www.enermaxusa.com/catalog/ticket_status
Please let us know if we can assist you any further
www.enermaxusa.com
_______________________________
Power Guy
Corsair Power Guru
Thanks for the message. I actually recommend a 40-70% load if possible. Here's why.
This is the efficiency curve of the HX series, which is somewhat common
for 80+ rated PSUs. The idea is that you want to be at that peak or
near it as much as possible. So yes, you could be at 20% or 80%, but
the problem with being very close to max load on a PSU is that it
stresses components. For maximum lifespan, matching a 40-70% load is
the best efficiency and will allow the PSU to last a bit longer.
** I asked the PowerGuy if he had any data to support the "a bit longer"
claim since the HX series is still 81% efficient @ 80-100% loads. If those high loads do affect the life of the psu surely there would be data to support it.
______________________________
Don't get me wrong, I'm not trying to tell everyone to run out to purchase a
bare minimum psu. However If you aren't running
SLI or a high-end system there is absolutely no reason to purchase a >500W psu
unless:
- you have money to burn
- you're considering a mediocre or mid-range psu
- you simply want additional headroom for future
expansion (SLI, CrossFire, HD 2900XT, multiple high wattage cpu's, exotic cooling, etc.)
I'll update this thread as I receive responses from other psu mfg's. Feel free to post your thoughts as well. The next question you'll probably be asking is how to tell if the psu
that you've picked out is high quality or a junker. You cannot judge a psu on name alone, so here is the Recommended PSU List