Testing and Results

Unlike most computer parts, power supplies require rather specialized equipment to test correctly. Sure, you can plug it into a computer system and see if it can run a 980x and a couple GTX580s, but that doesn’t tell you how much power the PSU is putting out, nor what that output looks like. Worse, if the unit is defective or simply underbuilt/overrated the unit can fail catastrophically and take your computer along with it!

Hence, you really need a load that is strong enough to stand up to a PSU dying while attached to it! Purpose built loads and the testing units to run them cost thousands of dollars. They’re easy to use and very accurate and definitely the ideal way to test power supplies, but also entirely too expensive for me to afford. Instead I have built my own! It’s entirely mechanical and not automated in the slightest, but it can put a serious load on a PSU and will survive the PSU fails in the process. The down side is that it doesn’t have the built-in current sensing that a professional grade unit does, so PSU efficiency is difficult to nail down.

The second part to a good PSU review is an oscilloscope to look at the outputs and check for ripple (I’ll talk about what ripple is in the ripple section), for this purpose I have a BK Precision model 1472B analog scope. It has its pluses and minuses compared to more modern USB scopes. On the minus side, taking pictures of it is a difficult operation at best as you’ll see. On the plus side, it has incredible sensitivity at high frequencies, something that many USB scopes lack.

Lastly, a voltage meter is required, I have a nice cheap unit that I have compared against a highly expensive Fluke 88 and found to match to within 10 mV. That’s good enough for me!

On the procedure end of things, I first check the voltages and ripple with no load on the PSU at all. This is a quite unrealistic test and many PSUs do not appreciate it at all, but I like to test it anyway. If the zero load results are terrible I put a small load on the PSU to simulate idle conditions with a low power computer and test the ripple again. Some PSUs are specifically rated for zero load operation, though this is not one of them.

With that out of the way, I put successively higher loads on the PSU and check the voltages of the three main rails at a SATA connector, all the way up to the PSU’s maximum output.

At the maximum output comes the last test, ripple at full (or very close to it) load. This does assume that the PSU didn’t explode on the way to full load of course! I’d be quite surprised if the quality PSUs I generally review were to explode, but it happens on lower end units sometimes.

The 12V, 5V and 3.3V rails need to stay within 5% of their official value to stay within spec, closer is ideal of course. That means 12V needs to be between 11.40-12.60V, 5V needs to be between 4.75-5.25V and 3.3V needs to be between 3.135-3.465V.

With that out of the way, lets move on to the output chart. I upgraded my PSU tester specifically to deal with this unit’s huge output rating, and I’ll be taking it to ~100.0% of it’s rated maximum load!

We’ll start with zero load and work our way up to that 100% number, and then do a bit of crossloading. I don’t expect this unit to have any issue at all with crossloads as it’s a DC-DC unit.

The first thing I do is plug in my Thermaltake Dr. Power II PSU tester to get a quick look at things, as well as to put a load on the 5vSB line.  Tragedy struck when I plugged it in however, as the Toughpower XT's ATX24P connector clip decided it had had quite enough and broke off.  This is rather of a mystery to me as it was being plugged in the correct way and hadn't been abused.  I can only guess that something unfortunate happened to it during manufacture.  The clip isn't required, but I'm not well pleased by it breaking off.

On the plus side, the Dr. Power II's opinion is that the PSU is quite happy.  The Power Good signal time is another thing that the Dr. Power II checks, this PSU hits the average time perfectly, as well as looking good overall.

Now lets start loading the unit down, and see how it does!

That right there, especially if you dump the "unfair" zero load numbers, is some epic regulation!  Ignoring the zero load numbers the 12 V rail deviates 00.5%, the 5 V rail deviates 00.4%, and the 3.3 V rail deviates 00.9%.  That's under 1% across the board, and is fantastic.  If you want to include the zero load 12 V result, it came in at 01.3% regulation, which is still excellent.

This is usually where I talk about how much noise the fan made.  This time it won't be.  Why?  Because the fan made no noise at all.  It didn't even turn on, in fact!  That's right folks, this PSU happily sat there putting out 1275w with passive cooling only.  My test environment was fairly cold (funny thing about winter...), which is a factor, but this is still very impressive.  I checked for excessively hot air coming out of the PSU a few times and while some warm air was rising from it, it was far from what I would call hot.  I'm impressed.

During the Dissection phase I packed some thermal transfer compound under and around the fan's sensor and repeated the testing, the fan still did not come on for a substantial period of time, even though I first heated the unit up to around 130f on a heater vent before testing.  After that preheat, it took around ten minutes of 1323w load to convince the fan to turn on, once it did the exhaust air was pleasantly warm, far from hot.  The fan itself was nice and quiet.

At higher load levels there is a bit of a 60hz hum that comes from the unit, in feeling the unit with my hand the hum is actually coming from the unit moving on my test bench!  Bolted solidly into a case I think it would likely disappear, and it was far from loud in the first place.

Next up, ripple testing!

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