Originally posted by: JEDIYoda
Power Supplies can be a huge pain in the butt if all your looking at are the specs verses $$$$$....
Here`s why....
Sure PSU #1 could be rated at 500watts continious power....
But PSU #2 could also be rated at 500watts peak power....
Any difference in the 2???
Then PSU #1 thats rate at 500watts is rated in a room at 25c....
then you have PSU #2 rated at too watts in a room thats say 5oc....
which of the 2 do you think is more accurate?
Because we all know that as the temperature goes up your rated power actually takes a huge hit.....
Thus would you want the PSU thats rated at 500 watts @ 50c or the PSU thats rated 500watts @ 25c??
Then another isuue you have is the workmanship....
The standard rule of thumb is if you have a light weight PSU then most likely your probably have a PSU thats not very well bult -- in terms of lasting along time or in terms of handling extreme loads or even normal loads for any length of time.
Heres excerpts from this article....
http://www.pcpowercooling.com/about/interview.php
CPU: One of your apparent pet peeves has to do with PSU temperature ratings. Why exactly?
Dodson: People don?t understand that the actual temperature that the power supply and its components see is far higher than room temperature. When a power supply is rated for 25 degrees C, like most of our competitors, especially the ones that are designed for home use, that?s a totally fabricated number put together in order to exaggerate the wattage claim.
CPU: Why fabricated?
Dodson: There is no way in the world that the air going to the power supply is going to be 25 degrees Celsius in the real world because with a 15-degree buildup inside the machine first, before the air reaches the power supply, that means that the room temperature would have to be 10 degrees C. Now you?re talking about it being in the 50s Fahrenheit. What these guys selling power supplies rated for 25 C are saying is that as long as you use the power supply in a room that?s 50 degrees Fahrenheit, you?re OK. But if you were to actually go through the de-rating that they keep very secret and re-rate those power supplies that are rated at 25 C at a more realistic 40, you?d have to cut the wattage rating by at least 33%, compared to what they?re advertising. You have a 400W power supply, but the fine print is, yeah, at 25 degrees C. At 40 degrees C, it?s a 300W power supply, and the public doesn?t understand that it?s not getting an apples to apples sort of rating when it is out there, buying it in the store, because these manufacturers don?t even specify what the ambient temperature is for full load. That?s one of the most common deceptive practices in the power supply business.
CPU: But if this were such a big deal, shouldn?t it have been more publicized by now? Does it really matter in the real world?
Dodson: For the last five years, companies have been marketing power supplies as being 400W and 500W on this basis. And they?ve been getting away with it without any sort of testing or validation by anyone. The reason they got away with it is because computers, up until recently, only needed like 300W. Since they only needed 300W and were actually capable of 300W, you don?t get caught if you?re saying yours is 500W. You only get caught when suddenly there?s technology that really needs 500W. For SLI you?ve got like 200W just for the video and another 120W for the CPU. So when the temperature inside the power supply starts getting way high, and it?s not designed for that, before you know it power supplies are just crapping out left and right. They were never designed to produce a realistic, true 500W in the first place.
CPU: So if we buy a 500W PSU with accurate thermal considerations, we?re good to go?
Dodson: Actually, it really isn?t the wattage of the power supply that counts today, because if it?s all on the wrong rails, it doesn?t do you any good. The only rail that matters whatsoever in today?s systems is the 12V rail. That?s because the video cards, CPUs, and drives are all being run from it. If the power supply design isn?t recent and doesn?t take this fact into account, it doesn?t matter if you have a 500W power supply, if it only has 20A of +12V power. You?ll see 600W power supplies that are down at 24A, whereas our 510W puts out a continuous 34A. That?s 50% more power than a power supply that, by wattage, is rated higher than we are.
CPU: Should people focus on peak or continuous power ratings?
Dodson: You want to zero in on the peak rating of the 12V output and how long that rating is for. If you get a 15-second rating on that and you have plenty of amps, then you know that even if you have eight to 10 hard drives, you?re going to have no trouble bringing them up simultaneously, with no need for sequencing or a second power supply. But a one-second peak isn?t going to get you anywhere. If it puts out the power for one second, that?s not enough time for the drives to get going.
CPU: But drives have very little draw.
Dodson: Well, drives on startup have 300% more draw than they do after they?ve stabilized. So even though they may not require much once they?re running, like say they require an amp of 12V, which would be 12 watts. Well, at startup, they could require 3A, which is 36 watts. Now if you have, say, five of them, that?s a 180W peak load at startup, which would be enough to bring a lot of power supplies to their knees.
