Load Testing Part One: Regulation
A decent load test of a PSU requires a decent load. Contrary to what some may believe, that means you need a known load that can fully stress the PSU. Computer hardware does not cut it. Worse, if the PSU fails during testing it might take out the computer hardware anyway. Commercial load testers cost a lot of money. I do not have a lot of money, so I built my own with juicy power resistors and a Toyota cylinder head. It works great. I’ll be using it to load this thing down fairly severely and will check voltages and ripple (more on that later) at various points. The down side to my tester is that the loads it can put on PSUs are fairly coarse, they go in increments of 48 W for 12 V, 50 W for 5 V and 22 W for 3.3V. Those wattages assume the PSU is putting out exactly the official rail voltage, a PSU putting out 12.24 V rather than 12 V will be at 49.9 W per step rather than 48 W. I file that under the “tough beans” category as I figure if a percent or two of load makes that much of a difference, the PSU manufacturer should have hit the voltage regulation more squarely. It does make calculating efficiency difficult at best. However, given that the input power is read via a Kill-a-Watt, the efficiency numbers are dubious to begin with. Kill-a-Watts are not known for extreme accuracy on things with automatic power factor correction. For this reason, I am not listing the efficiency.
The ATX spec says that voltage regulation must be within 5% of the rail’s official designation, regardless of load. It doesn’t actually mention that the PSU shouldn’t explode, though I expect they figured it was implied. Exploding is a failure in my book regardless.
It is also worth knowing that I will be testing this PSU at both outdoor ambient temperatures (typically between 10 °C and 20 °C here this time of year) as well as in the Enclosure of Unreasonable Warmth. TEUW is a precision engineered enclosure that I use to route the exhaust air from the PSU right back into the intake fan, it is adjustable to hold the intake air temperature at (almost) any level I want it. This way I can test the PSU’s response to hot conditions as well as cold conditions. For the hot testing I will be running the intake temp as close to the unit’s maximum rated temperature as possible. TEUW, in case you’re curious, is a cardboard box.
| Wattages (total) | 12 V Rail | 5 V Ral | 3.3 V Rail | Kill-A-Watts | Temps In/Out |
| 0/0/0w (0w) | 12.22 | 5.17 | 3.38 | 9.2 | 10/10°C* |
| 96/50/22w (168w) | 12.18 | 5.09 | 3.34 | 191 | 11/10°C* |
| 288/50/22w (360w) | 12.18 | 5.09 | 3.34 | 399 | 12/9°C* |
| 480/50/22w (552w) | 12.18 | 5.09 | 3.34 | 613 | 12/9°C* |
| 672/50/22w (744w) | 12.14 | 5.09 | 3.34 | 833 | 8/32°C |
| High Temperature Results Below: | |||||
| 672/50/22w (744w) | 12.14 | 5.09 | 3.35 | 844 | 51/63°C |
With the fan in don’t-move-till-it’s-hot mode the unit was perfectly happy to sustain close to full load (in, admittedly, a pretty cold ambient) without the fan moving. The * results mark when the fan didn’t move. This is nice as the fan itself is fairly noisy, it has a whispery bearing noise as most ball bearing fans do, plus a low frequency mechanical noise starting at medium speed that I found fairly annoying. It’s unfortunate as the airflow noise and bearing noise weren’t at all obnoxious, but the mechanical noise was.
Regulation wise we’re seeing 0.6% on the 12 V rail, excellent! The 5 V rail comes in at 1.5% and the 3.3 V rail at 1.2%. Averaged together we have a final result of 1.1%, just shy of the excellent mark at 1%, but still very very good.
With the exception of the fan this unit passed with flying colors, the fan is something I wouldn’t want running at mid speed on my desk. Under my desk it’d likely be fine.
