i have a wattage wall meter that tells me efficiency readings of devices
How? A watt meter tells you the total amount of power being pulled from the wall, but it does not tell how much power the connected device is wasting in the form of heat, at that point in time. In other words, I don't see how it can't tell you the efficiency of the connected device. You would have to already know how much power the connected device is outputting (or putting to "work") at that point in time.
For example, assume an 80% efficient PSU. If the computer (CPU, motherboard, RAM, graphics card, drives, fans, etc.) is demanding 300W, it will pull from the PSU 300W (regardless if the PSU is a 350W, 500W or 1000W PSU). But the
Kill-A-Wall Meter the PSU is plugged into will show 375W with that 80% efficient PSU (375 x .8 = 300). 75W is being wasted in the form of heat.
Unless you knew somehow already that the computer components were demanding 300W, that 375W reading on the Kill-A-Wall meter only tells you how much the PSU is demanding. It does not tell you the efficiency of the PSU (how much power the PSU is wasting in the form of heat).
Take that same 300W computer connected to a different PSU. Now the Kill-A-Watt meter shows 333W. What does that tell us? If we didn't already know for a fact the computer was demanding 300W, we would not know what that 333W means. It could mean the computer was demanding 233.1 watts and the PSU was an inefficient 70% supply (333 x .7 = 233.1).
But since we know the computer is demanding 300W, the 333W Kill-A-Watt reading tells us that is a 90% efficient supply (333 x .9 = 299.7).
There really is no way an "average consumer" can do this. That's why we have to rely on the professional review sites as they have (1) the expertise and (2) the necessary (and expensive!) power supply analyzers that not only read how much the power supply is demanding, but they measure how much power the PSU is outputting too. You have to know both to determine the difference. Ideally, the ratio would be 1:1. But that will never happen. There will always be some energy loss when converting AC to DC.
You can't really use a computer to test a PSU's efficiency either because a computer's demands are constantly varying. You need something that can present the PSU with a pre-determined load (or preferably, a wide variety of expected loads).
Back in the day (before 80 PLUS and good review sites) I would test PSUs with my trusty 300W 10Ω ceramic power resistor ("dummy load") similar to
this one (mine is variable with a sliding tap on one end to adjust resistance as desired). We knew how much power the PSU was demanding from the wall, we knew the exact load, the exact output voltage, and the current. So it was not hard to determine how much power was being wasted. BTW, that dummy load would get
HOT!!!
Another problem for the "average consumer" is PSUs output 3 voltages (+12VDC, +5VDC, and +3.3VDC) simultaneously on multiple rails. Some PSUs even have multiple 12V rails. To properly test the efficiency of the PSU, you really need to test all the rails at once, or at least properly terminate with a known value the unused rails while testing one of the rails. This is because some power is always consumed on every rail, even when no load is presented to that rail. So even though it would be a tiny bit, that would still skew your efficiency results if you did not properly take them into consideration too.
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@lynx29 Not sure why you want to measure efficiencies here - if just curious or if you really want to know the status of these PSUs. I recommend you not worry about efficiencies because it is just too complex (and expensive) for the "average consumer" to test for. But I think it would be a good idea to test these old PSUs to make sure they still work.
A
PSU Tester can be real handy for this. The advantage of this model is that it has a LCD readout of the voltages. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within the
required ±5% tolerances (at least with the tester’s internal load) as specified by ATX Form Factor PSU standard. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". However, none of these testers test for
ripple and other anomalies that affect computer stability. That again, requires sophisticated and expensive test equipment, and the knowlege to use them and properly interpret their results.
Also, these testers only provide a small "dummy load", not a variety of "realistic" loads. So while better than nothing (or a paper clip!), using one of these testers is helpful, but still not a conclusive test.
You can use a multimeter, but again, to get conclusive measurements, the supply needs a proper load. This means it would have to be connected to a working motherboard. This is very inconvenient when testing several PSUs. One of those testers make it easy.
Acceptable Tolerances:
12VDC ±5% = 11.4 to 12.6VDC
5VDC ±5% = 4.75 to 5.25VDC
3.3VDC ±5% = 3.14 to 3.47VDC
That is the problem with just about all "hobbyists" and self-taught "experts" - they don't get the well rounded education needed to differentiate between the dime-a dozen-expert and the professional expert. But of course, education and experience alone, regardless how extensive and complete, still does not automatically make one a professional.
