Can someone explain why PSU Load Wattage is 50% or less than advertised Wattage?

[Ghetto_Child]

Ok so I'm reading the PSU roundup over here http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/695-skymtl-s-500w-sub-105-psu-roundup.html thanks to one of the users on RFD and now that I've reached the graphs of PSU load I'm confused. I don't see why the load wattage should be <=50% of advertised wattage :confused: . Where does the rest of the power go? I always thought PSUs put out close to their advertised wattage.

On a side note I just realized my PSU has Active PFC. I bought my IBM NetVista in first quarter 2001 and it has Active PFC :-0

[Amourek]

Advertised wattage? It only pulls as much power as needed.

[Ghetto_Child]

then I don't understand the reviews, all the PSUs are pulling less than the advertised amounts. So why is SKYMTL dissapointed with the results?

Quoted from SKYMTL @ http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/695-skymtl-s-500w-sub-105-psu-roundup.html
http://www.hardwarecanucks.com/imagehosting/2404603313667a08.jpg

By looking at this chart we can understand why some computers fail to boot when coupled with a cheap or under-powered power supply. Upon startup, a computer consumes an amazing amount of power which may be too much for an inadequate power supply.

Results:

FSP Blue Storm: I was pleasantly surprised with the efficiency of this power supply. Even though it didn’t live up to the numbers that the Silverstone was pushing out, it was quite close across all of the tests. A very good showing by FSP.

Cooler Master 600W: This power supply really proved to be a disappointment because I was really hoping to see some better efficiency results. Instead, it gobbled up over 40W more power at load than the Silverstone. Just to be sure, I ran all the tests with the CM three times, all ended up leading to the same efficiency results.

Nmedia MP-500: Considering this is the least expensive power supply in the entire roundup, it put out some extremely respectable numbers. Even though we have once again proved that the “over 85% efficiency” listed on the box is false, the results are nonetheless impressive for a $60 power supply.

Enermax FMAII 535W: The Enermax netted the second highest load consumption which is not exactly something to be proud of but it did not come close to the power draw of the Cooler Master.

Silverstone ST50EF: Quite simply this is the most efficient power supply in this test. The FSP tried to give it a good run for its money but in the end, the Silverstone won by a fair margin. Considering this unit consumes nearly 20% less power than the Cooler Master, you can see that its 80+ certification is not just window dressing.

Mushkin HP-550: While this power supply is not as efficient as some of the others, it is a solid mid-pack performer. What should be noted is that even though the “Load” value is only 1W below that of the Enermax, the average consumption of the Mushkin was quite a bit below that of the Enermax. Since the values fluctuate so rapidly, I have no way to accurately log these peaks and valleys in consumption. Thus, this result only reflects the PEAK power consumption.

[Spare-Flair]

Can you read the title of the that chart? It says EFFICIENCY (lower is better).

If one of those PSUs actually pulled 500w at load while the rest of the playing field was only pulling 280w max from the same system, it'd be utter crap! Ridiculously inefficient. Again, what this demonstrates is that marked wattage is overrated for powersupplies and is more or less a marketing device. Any cheap, crappy PSU could be rated for a high wattage but have crappy rails, unstable voltages, poor reliability, crappy sinks, and overall efficiency. I'm running my system on a tiny 250w PSU.

And I have no idea where you are reading that the reviewer is disappointed in the results. He is disappointed the others aren't as efficient as the Silverstone PSU and that one is his the winner of the review.

[Ghetto_Child]

then I don't understand the reviews, all the PSUs are pulling less than the advertised amounts. So why is SKYMTL dissapointed with the results?

Quoted from SKYMTL @ http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/695-skymtl-s-500w-sub-105-psu-roundup.html
...Cooler Master 600W: This power supply really proved to be a disappointment because I was really hoping to see some better efficiency results. Instead, it gobbled up over 40W more power at load than the Silverstone. Just to be sure, I ran all the tests with the CM three times, all ended up leading to the same efficiency results...


Ok I did use the wrong wording I should have asked why he's dissapointed with the results of 1 PSU in particular. What I asked was why he had any dissapointment at all. Again I already said I don't understand the review.

Furthermore you didn't answer my question at all so I'm still at a loss of understanding what the chart means. So you stress it's an efficiency test, ok efficiency of what making hot air :confused: Really I don't know what the chart is supposed to be saying. I originally thought the chart is saying how much power the PSU is giving to the computer and how much power the computer is able to pull from the PSU. What's the perspective? Ice to water is an endo-thermic reaction but the same water to ice is an exo-thermic reaction, the difference is perspective.

[tdotcbc84]

off topic...

but I can't handle ur avatar! *barf*

[goofball]

Furthermore you didn't answer my question at all so I'm still at a loss of understanding what the chart means. So you stress it's an efficiency test, ok efficiency of what making hot air :confused: Really I don't know what the chart is supposed to be saying. I originally thought the chart is saying how much power the PSU is giving to the computer and how much power the computer is able to pull from the PSU. What's the perspective? Ice to water is an endo-thermic reaction but the same water to ice is an exo-thermic reaction, the difference is perspective.

Efficiency comparison of how much AC each PSU requires to power the same components. The more AC the unit needs to power the same components in comparison, the more that is wasted (less efficient).

What the chart is saying is how much power is being drawn from the wall (AC). He is not trying to put 500w DC load and see how long the PSU lasts or anything with these efficiency tests. You also have to note that most people don't really draw 500w DC from their PSU, it takes a very high end system to do that.

It's not exactly the same but it's like comparing car engines of the same displacement and why one burns more fuel than another.

[Spare-Flair]

Ok I did use the wrong wording I should have asked why he's dissapointed with the results of 1 PSU in particular. What I asked was why he had any dissapointment at all. Again I already said I don't understand the review.

Furthermore you didn't answer my question at all so I'm still at a loss of understanding what the chart means. So you stress it's an efficiency test, ok efficiency of what making hot air :confused: Really I don't know what the chart is supposed to be saying. I originally thought the chart is saying how much power the PSU is giving to the computer and how much power the computer is able to pull from the PSU. What's the perspective? Ice to water is an endo-thermic reaction but the same water to ice is an exo-thermic reaction, the difference is perspective.

It seems you really don't understand what a powersupply really does...or even how to read a chart :D (just kidding) Look at the chart's title which is efficiency and the Y-dimension is wattage. It's energy efficiency, not hot air efficiency. :cheesygri He is measuring the maximum powerdraw from the outlet. A watt is a measure of energy over time, not a measure of total energy output. The system tested probably only needs to draw less than ~230W to operate at load. That's why all the PSUs peak at under 280W on that chart It's an energy efficiency test. The more efficient the PSU design, the less the power draw by the computer since the power neccessary to be drawn by the PSU to keep the computer stable at load varies due to the efficiency of their designs. The lower-quality the PSU, the higher the wattage neccessary to power the computer because more energy is wasted.

Like the above poster, this is totally not the same, but to get you to understand, think about it like this:
You have 5 cars that are all about the same curb-weight and engine displacement. Yet one of the cars made by Coolermaster turns out to be less efficient and it's fuel economy is only 25 miles/gallon to the Silverstone which gets 30 miles/gallon. For the Coolermaster car, it takes 1 gallon of fuel to go 30 miles. For the Coolermaster PSU, it requires 276W to power the computer at load while the Silverstone PSU only needs 233W to power the computer at load (which means the computer is actually requiring less than 233w to operate at load)

Energy efficiency and stability of the other factors he tests like voltage regulation and AC ripple are the important things to look for in a PSU. Wattage means next to nothing because the average consumer is not going to have a system that draws enough power to max out a PSU rated for 500w unless you have a great deal of hardware (multiple harddrives, multiple fans, multiple cards). My system is made out of about the same components as the reviewers and again, I can run it stable and perfectly fine with an efficient PSU that's only rated for 250w! The computer only needs < 230w (joules/second) to operate and yet the Coolermaster is struggling and wasting electricity (probably as heat), etc. and ends up drawing almost 280w from the wall-outlet. That's 50w being wasted as heat!

[Ghetto_Child]

Before I read your entire post spare-flair I know what watts are. I earned 100% on electricity in high school Physical Science, I can't remember if we studied electrical circuits in Physics 536. Anyway watts are power, volts x amps = watts = power, and I think volts/amps = ohms. Volts = Joules/sec, amps = Culombs/sec. My problem before was I did not understand the perspective of the charts/test. Yes the chart said efficiency but to me who's never done these tests before I didn't know what he was measuring efficiency of. That's why I sarcastically stated "hot air".

Goofball explained it perfectly for me and I thank him immensely for that. Now the chart makes sense, how much AC Watts required to produce necessary DC Watts. Or how much power the PSU itself requires to operate. This was not clear to me when I was reading the review so now I understand.