Egads! Yet another longish post from Crisspy for Mike... sorry Mike...
For the second experiment assume again two electrically identical PSUs (identical fan), one with large heatsinks and one with small heatsinks. Naturally the PSU with larger heatsinks is more efficient at moving heat into the air. It is said to have greater thermal efficiency. The temperature of the air exhausted from the high thermal efficiency PSU will be warmer then the PSU with lower thermal efficiency, because more heat is transferred out though the exhaust fan.
Many other points in the post are right-on, but this one skipped a beat. Total heat in = Total heat out.
The smaller heatsink
will get hotter because it's shedding the same watts in less area. The hotter heatsink might fiddle the electrical performance a wee bit, albeit not much. It might sink a bit more into a metal case too, again very minor. Still, after warm up, the air temp out will be the same for both PSU's
because there is the same power output from both, going into the same amount of air.
The differences in fan volume between PSU's complicates these tests badly though.
A valid solution is to measure and report airflow. How to do it accurately? Would it work well? I don't know, haven't done my homework. Check this out. $120usd, might work.
In the spirit of what a real-world-ish empirical test can expose, you would see straight-off what the strengths and weaknesses of different PSU's are. And that is very valuable information.
Otherwise you could go nuts and swap in standard panaflo's. Then any differences would be due to airflow impediments that you could rightfully fault the PSU for, and even suggest remedies for. You would still want to measure airflow for a well rounded picture. This isn't too far out, it's the most expected and accepted repair/mod for PSU's. And some PSU's might just be a-beggin' for a quiet fan. Their makers might oughtta know in time for the next model release. But then there's so many thermal control reliant ones
Testing in a real case would likewise be smart since sinking heat to the case is a potentially valid stategy, even a primary method for some small form factors that are definitely within the scope of our interests.
What we want is quiet computers. We want to know how a real PSU performs as part of a real system. What it's weaknesses are, and why. A PSU that is quiet with high airflow, but a little inefficient, might waste a few more watts, but still help cool a whole system better, and therefore be a really good buy. It might even avoid a second exhaust fan. Maybe it would allow a quieter system than one with a quieter PSU + second fan. It's a big mixed bag of conflicting priorities, and the real trick is to find out what works well, for real, and why. And if not, why not. Empirical testing is the only thing that might sort it all out.
So I suggest (revisions revisions):
-realistic testing case.
-well controlled sealed air flow.
-fixed area passive air intake at bottom front, well larger than both fans.
-mixing ducts out back.
-case exhaust fan/s (std. panaflo) at upper-middle back (typical)
-PSU inside powering reference load resistors for a typical system load.
-airflow from each fan. ( case fan/s won't vary significantly for a given voltage), and at intake. F1+F2=F3?
-load voltage. +12+5+3.3, actual load wattage use V*V/R (measured more to check for working regulation)
-mains voltage and amperage for total input wattage.
-temps: each exhaust stream, inlet stream, some spot near where CPU would get air?
-sound levels out back, front, and side
trials / things to fiddle and combine:
-case panaflo/s @ 12v, 7v, 0V/sealed off
-PSU at idle, 100w load, and 200w load
-stabilized PSU fan speeds before the measurements are taken, or attempt to record highs/lows.
what it all tells us:
-efficiency of PSU in a realistic setting.
-performance of PSU in a realistic setting.
-PSU's thermal contribution to a realistic system.
-temperature performance of a realistic system.
-thermal viability of simple & realistic configurations.
-might we need a second case fan? if so, easy to approximate how much.
-how badly will our ears bleed at the end of the day?
-we might even get a clear idea as to what PSU's are worth buying and why.
Is it all worth it? That's obviously up to you Mike. I don't think your compulsion to work too much was completely wrong on this idea.
As for realiablility / hot spots: off the lid; off the fan; standard medium reference breeze from a fan; plug into load tester; power up; look for hot spots with IR thermometer
. That's basically what they do during good design, but with an IR camera. Would certainly be interesting, and could at least indicate an all's-cool / warm-spots / hot-spots / run-she's-gonna-blow type rating. Note too that most component types have fairly generic temp ratings, so a generic above-sane-hot-spot warning could be indicitive of likely trouble. A thermal under-the-hood with a "Don't do this at home kids" lable. But still, do we really need to know?
I am reminded of quokked's sig. And I promise I'll run out of time soon, or get a life, or something...
At least I'm enthusiastic.