Originally Posted by nanotm
well its been my personal opinion that since the sweet spot of efficiency is between 50%>80% load on the psu your best of determining what your peak power draw should be cpu+gfx +100w (average for ancillaries) (most often somewhere around 500>650w meaning you should be looking at between 850 and 1000w psu's to be within the peek efficiency curve for hte psu (this also means its not likely to get warm through use nor need more than around 30% fan speed even on the hottest days) this will also mean that providing your running from a stable supply its unlikely to make any noise
No, no, no, no. It doesn't work that way. Your understanding of it is not quite correct (but then MOST people don't understand it correctly). Yes, most PSUs should give their best efficiency when the power consumption is between 40% and 60% of its total output capacity, but there's more to understand than just that alone. You want your average
power consumption to fall in that range, not your peak. Even then, this really doesn't apply to today's good PSUs like it did to PSUs from many years ago. Some good PSUs today give their best efficiency at almost any
power draw. So this is really an obsolete concern and there's really nothing more to discuss.
However, if one were to insist that this is important for them, then again, they should figure out what their average power consumption will be day to day and then base their purchase on that.
So, ok, let's say your most demanding activity is gaming and let's say you only do that for a couple of hours every day and the rest of the time your system is either idling, or under VERY low loading conditions, or off completely. That's a VERY low average power draw. Let's say the power consumption while gaming is precisely 500W. With everything else being the same as I just described (resulting in the extremely low average power draw), you could power this just fine with a high-end 550W PSU if you had to
and you'd be fine and your average efficiency would still be quite good and this PSU would give you years and years and years of excellent service.
Now, let's take this in the complete opposite direction and say that your system is at full load 24/7. Maybe it's Folding and mining at the same time 24/7. Let's assume it is, and let's assume the power consumption is 500W. For THIS particular system and loading scenario, the average power consumption is 500W. That's enormously different from the previous situation where the average loading condition was extremely low. For an average load of 500W, yeah, I would recommend nothing less than a high-end 850W PSU. I would be foolish to recommend anything less than that for a 500W average power draw.
So you see, you can't just say "well, my peak hits 500W, so therefore I want an 850W PSU or bigger".
I don't want to hear about keeping the PSU cool either. With today's good PSUs, if you choose to keep your average power consumption at 40-60% of the total output capacity (which would be at least 100-200W higher than the continuous
wattage rating that's advertised), then you're looking at a life of over 10 years for that PSU. Easily. Probably far longer than 10 years.
Yes, the GOOD
PSUs only advertise their continuous
wattage rating, not their absolute peak. So that 550W PSU I mentioned might actually have a peak of 750W, especially if it's a very high-end unit. Think about that for a while!
The continuous rating means exactly that: continuous. 24/7. Non-stop. Imagine how damn good the PSU has to be in order to deliver 550W continuously. Why worry about pulling 500W out of a PSU like this for a few hours every day?! Right?!?! Right.