ASUS U-75HA 750w ATX PSU
To provide our readers with the most accurate results, Overclock3D uses a professional grade SunMoon SM-268+ ATE load tester capable of placing a sustained load of 1690w across a total of six rails (including +5vsb and -12v) on the PSU. Unlike our previous resistor based load tester the SM-268+ gives us the ability to adjust amperage loads in increments as small as 0.01A while also measuring voltages and wattage readings on-screen.
During todays tests we will be placing the U-75HA under 25%, 50%, 75% and 100% load levels and taking voltage readings at every stage. The chart below details the exact amperage load placed on each rail of the PSU at the aforementioned load levels:
|+12v1 / +12v2 *||6.75A||13.50A||20.25A||25.00A|
|+12v3 / +12v4 *||6.75A||13.50A||20.25A||25.00A|
| Total **||215.8W||429.0W||641.8W||764.0W|
* Rails 1&2 and 3&4 on the U-75HA have been combined during testing on the SM-268+ due to a limitation with the testing equipment. However, as the U-75HA features only one +12v transformer this becomes irrelevant as we are effectively re-joining virtually split rails.
** Total wattage is taken directly from the SM-268+ readout rather than a calculation of the amperage loads.
Now that we've seen exactly what load we're placing on the U-75HA let's see how it performed...
|+12v1 / +12v2||12.16v||12.12v||12.08v||11.89v|
|+12v3 / +12v4||12.15v||12.11v||12.07v||11.70v|
At 25% and 50% loads we get a chance to see the voltage output of the rails close to what they have been set at in the factory. Unlike some less reputable manufacturers, ASUS has chosen not to over-volt the rails in an attempt to keep voltage readings looking good when a heavy load is applied. Both the +3.3v, +5.0v and +12v rails sit comfortably within 2% of their ideal voltages.
Moving on to 75% load the voltages take a small dip, but aside from the slightly low 3.22v output from the +3.3v rail there's nothing much to worry about.
Finally at 100% load everything goes down hill with +3.3v rail coming extremely close to falling outside the ATX +/-5% requirement. The +12v3/4 rails also take quite a dip down to 11.70v which is still within ATX spec but would have most hardcore enthusiasts running for the hills. All other rails remain reasonable, but the performance certainly isn't anything to shout about.
Efficiency tests are performed by measuring the wattage consumed by the power supply at the mains (Mains Draw) against the wattage readout displayed on the SM-268+ load tester (PSU Load). These results should offer around 99% accuracy placing them extremely close to results obtained from professional equipment.
| Mains Draw||256w||499w||752w||917w|
| PSU Load||215.8w||429w||641.8w||764w|
ASUS claim that the U-75HA is capable of up to 86% efficiency and judging by the results we obtained this is certainly very close to the truth. At 50% load the U-75HA was drawing a total of 499w from the wall socket and the SM-268+ load tester was reporting a load of 429w. By taking both of these figures and applying some simple math (Load / Draw * 100) we arrive at a result of 85.97% efficiency.
Considering that most mid-range PC systems with single high-end graphics cards will consume somewhere in the region of 450w its good to see that this is where the ASUS delivers its best results.
As with all components in the modern computer system, the performance of a PSU can be directly affected by heat. Excess levels of heat recorded at the PSU's exhaust can indicate that the cooling system is inadequate in keeping the PSU's internal temperature under control which can subsequently lead to a reduction in the maximum power output of the unit. For this reason Overclock3D takes temperature readings from the PSU's intake and exhaust areas after 10 minutes of running at each specified load level. These results can be seen below.
With a maximum exhaust temperature of 29.3°C when under 100% load, the U-75HA certainly doesn't show any signs of overheating. This is undoubtedly down to the high efficiency of the unit (less energy being wasted as heat) and the 135mm fan. Even at 100% load, the U-75HA hardly increased the fan speed to combat the additional heat and as a result the unit remained fairly quiet. While we would like to make an official comment on the noise output of the unit, the SM-268+ load tester is far too noisy and prevents any measurements - subjective or scientific from being taken.
In our continuing efforts to increase the quality and accuracy of reviews here on Overclock3D we recently invested in professional PSU load testing equipment. However, while this allows us to place accurate load levels on a PSU during testing there are still several areas for improvement that you will see from us in the near future:
• Heat chamber testing. All PSU testing will be conducted at a standard temperature of 50c.
• Digital Oscilloscope. For measurement of ripple and line noise.
• Variable AC Transformer. For conducting PSU reviews at both 240VAC and 120VAC mains voltages
• Digital Tachometer. To observe fan speed as temperature and load increase.
• Noise Recordings. Allow readers to experience the noise emitted from the PSU for themselves.
Providing we still have access to the ASUS U-75HA once our updated testing suite is in place we will be sure to update this page of the review with the additional results.