Test SetupAll measurements are performed utilizing ten electronic loads (seven Array 3711A, 300W each, and three Array 3710A, 150W each), which are able to deliver over 2500W of load and are controlled by a custom made software. We also use a Picoscope 3424 oscilloscope, a CHY 502 thermometer, a Fluke 175 multimeter and an Instek GPM-8212 power meter. Furthermore, in our setup we have included a wooden box, which along with a heating element is used as a Hot Box. Finally, we have at our disposal four more oscilloscopes (Rigol 1052E and VS5042, Stingray DS1M12 and a second Picoscope 3424) and a CEM DT-8852 sound level meter. In this article you will find more details about our equipment and the review methodology we follow. Finally, if the manufacturer states that the maximum operating temperature of the test unit is only 40°C then we try to stay near this temperature, otherwise we crank up the heat inside the hotbox up to 45-50°C. Since this unit has 45°C max operating temperature we will stick close to this one.
Voltage Regulation ChartsThe 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 Regulation ChartThe following chart shows how the 5VSB rail deals with the load we throw at it.
Efficiency ChartIn this chart you will find the efficiency of ZT 750W at low loads and at loads equal to 20-100% of PSU’s maximum rated load.
Voltage Regulation and Efficiency MeasurementsThe first set of tests reveals the stability of voltage rails and the efficiency of ZT 750W. The applied load equals to (approximately) 20%, 40%, 50%, 60%, 80% and 100%, of the maximum load that the PSU can handle. In addition, we conduct two more tests. In the first we stress the two minor rails (5V & 3.3V) with a high load, while the load at +12V is only 2A and in the second test we dial the maximum load that +12V can handle while load at minor rails is minimal.
| Voltage Regulation & Efficiency Testing Data |
OCZ ZT 750W
|Test||12 V||5 V||3.3 V||5VSB||Power|
Efficiency is satisfactory for the Bronze certification the units carries while the capability to deliver full load at 45°C ambient is very welcome. With only 5°C difference from 50°C that ATX spec recommends we are not going to complain this time, since 45°C ambient surely is high enough. On the contrary, voltage regulation, although at +12V is below 3%, which didn't satisfy us since the competition scored better here. If +12V stayed within 2% then we wouldn't mind so much about the deviation at 3.3V, since this rail is lightly used in contemporary systems.
Efficiency at Low LoadsIn the next tests, we measure the efficiency of ZT 750W at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dial are 40, 60, 80 and 100W (for PSUs with over 500W capacity). This is important for scenarios in which a typical office PC is in idle with power saving turned on.
| Efficiency at Low Loads |
OCZ ZT 750W
|Test #||12 V||5 V||3.3 V||5 VSB||Power|
At low loads efficiency was at the expected levels, for a Bronze unit. With 40W it drops a hair under 70% and with 20W more it reaches 76%. Beyond 80W it passes the 80% mark, a satisfactory result for this test.
5VSB EfficiencyATX spec states that the 5VSB standby supply's efficiency should be as high as possible and recommends 50% or higher efficiency with 100mA load, 60% or higher with 250mA load and 70% or higher with 1A or more load.
We will take four measurements, three at 100 / 250 / 1000 mA and one with the full load that 5VSB rail can handle.
| 5VSB Efficiency|
OCZ ZT 750W
|Test #||5VSB||Power (DC/AC)||Efficiency||PF/AC Volts|
The 5VSB rail exhibited decent efficiency since at all tests it was above the equivalent thresholds that ATX spec sets. Even with 4A load, efficiency managed to register a peak, although the high voltage drop shows that such high load is near the limits of the 5VSB circuit.
Power Consumption in Idle & StandbyIn the table below you will find the power consumption and the voltage values of all rails (except -12V), when the PSU is in idle mode (On but without any load at its rails) and the power consumption when the PSU is in standby (without any load at 5VSB).
| Idle / Standby |
OCZ ZT 750W
|Mode||12 V||5 V||3.3 V||5VSB||Power (AC)||PF/AC Volts|
Like most other PSUs that we tested recently, phantom power is really low at 0.3W so the PSU passes the ErP Lot 6 requirements with flying colors.