Test SetupAll measurements were performed using two Chroma 6314A mainframes equipped with the following electronic loads: six 63123A [350 W each], one 63102A [100 W x2], and one 63101A [200 W]. The aforementioned equipment is able to deliver 2500 W of load, and all loads are controlled by a custom-made software. We also used a Picoscope 3424 oscilloscope, a Picotech TC-08 thermocouple data logger, a Fluke 175 multimeter, and a Yokogawa WT210 power meter. We also included a wooden box, which, along with some heating elements, was used as a hot box. Finally, we had at our disposal four more oscilloscopes (Rigol 1052E and VS5042, Stingray DS1M12, a second Picoscope 3424), and a CEM DT-8852 sound level meter. You will find more details about our equipment and the review methodology we follow in this article.
We conduct all of our tests at 40 - 45°C ambient in order to simulate the environment seen inside a typical system with higher accuracy, with 40 - 45°C being derived from a standard ambient assumption of 23°C and 17 - 22°C being added for the typical temperature rise within a system.
Primary Rails Voltage RegulationThe following charts show the voltage values of the main rails, recorded over a range from 60W to the maximum specified load, and the deviation (in percent) for the same load range.
5VSB RegulationThe following chart shows how the 5VSB rail deals with the load we throw at it.
Hold-up TimeThe hold-up time is a very important characteristic of a PSU and represents the amount of time, usually measured in milliseconds, that a PSU can maintain output regulations as defined by the ATX specification without input power. In other words, it is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption. The ATX spec sets the minimum hold-up time to 16 ms at maximum continuous output load. In the following screenshot, the blue line is the mains signal and the yellow line is the "Power Good" signal. The latter is de-asserted to a low state when any of the +12V, 5V, or 3.3V output voltages fall below the undervoltage threshold, or after the mains power has been removed for a sufficiently long time to guarantee that the PSU cannot operate anymore.
The hold-up time for 1.4 ms doesn't meet the ATX requirement, so the PSU will lose some performance points here. The hold-up cap apparently needs some extra capacity to cope with the unit's demands during this test.
Inrush CurrentInrush current or switch-on surge refers to the maximum, instantaneous input-current drawn by an electrical device when first turned on. Because of the charging current of the APFC capacitor(s), PSUs produce large inrush-current right as they are turned on. Large inrush current can cause the tripping of circuit breakers and fuses and may also damage switches or relays; as a result, the lower the inrush current of a PSU right as they are turned on, the better.
The inrush current reading that we measured is low enough, and this is a clear indication of a proper design.
Voltage Regulation and Efficiency MeasurementsThe first set of tests revealed the stability of the voltage rails and the efficiency of the MK3S750. The applied load was equal to (approximately) 20%, 40%, 50%, 60%, 80%, 100% and 110% of the maximum load that the PSU can handle. In addition, we conducted two more tests. In the first test, we stressed the two minor rails (5V and 3.3V) with a high load while the load at +12V was only 2 A, and, in the second test, we dialed the maximum load that the +12V rail could handle while the load on the minor rails was minimal.
| Voltage Regulation & Efficiency Testing Data |
PC Power & Cooling MK3S750
|Test||12 V||5 V||3.3 V||5VSB||Power|
|Efficiency||Fan Speed||Fan Noise||Temp|
|20% Load||10.551A||1.930A||1.955A||0.970A||149.70W||90.50%||0 RPM||0 dBA||49.06°C||0.940|
|40% Load||21.502A||3.886A||3.939A||1.170A||299.67W||92.34%||0 RPM||0 dBA||52.23°C||0.976|
|50% Load||26.877A||4.875A||4.946A||1.566A||374.64W||92.01%||1045 RPM||44.1 dBA||42.63°C||0.981|
|60% Load||32.256A||5.868A||5.968A||1.960A||449.49W||91.84%||1094 RPM||44.4 dBA||42.99°C||0.985|
|80% Load||43.233A||7.885A||8.027A||2.365A||599.44W||91.32%||1127 RPM||44.6 dBA||44.37°C||0.986|
|100% Load||54.859A||8.920A||9.102A||2.970A||749.24W||90.40%||1194 RPM||45.2 dBA||45.92°C||0.987|
|110% Load||61.167A||8.938A||9.141A||2.975A||824.04W||89.90%||1263 RPM||45.6 dBA||46.30°C||0.988|
|Crossload 1||1.969A||14.010A||14.005A||0.501A||143.10W||85.09%||1009 RPM||43.2 dBA||43.10°C||0.941|
|Crossload 2||61.933A||1.000A||1.002A||1.001A||758.35W||91.18%||1200 RPM||45.2 dBA||45.43°C||0.987|
Efficiency is very good and does, according to our experience, easily meet 80 Plus Gold requirements. The cooling fan didn't engage up to the 40% load test, and the ambient inside the hot box was very high. The fan's rotational speed remained low after it started spinning, even during the 100% and 110% load tests.
Voltage regulation at +12V is satisfactory, although we were hoping to see a reading below 1%. Readings on the minor rails are definitely not amongst the best we have ever encountered: the 3.3V rail even reached a deviation of 3%, which is not something we were expecting of this platform. That said, what counts more is the +12V rail, but some performance points will be lost on the minor rails.