Seventeam ST-750P-AF Power Supply Review
Load Tests
Contents
We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.
First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit beha
ved under each load. In the table below we list the load patterns we used and the results for each load.
If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.
+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests the +12V1 input was connected to the power supply +12V2 rail and the +12V2 input was connected to the power supply +12V1 rail.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12V1 | 5 A (60 W) | 11 A (132 W) | 16 A (192 W) | 22 A (264 W) | 27 A (324 W) |
| +12V2 | 5 A (60 W) | 10 A (120 W) | 16 A (192 W) | 21 A (252 W) | 27 A (324 W) |
| +5V | 2 A (10 W) | 4 A (20 W) | 6 A (30 W) | 8 A (40 W) | 10 A (50 W) |
| +3.3 V | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 8 A (26.4 W) | 10 A (33 W) |
| +5VSB | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 W) | 2.5 A (12.5 W) | 3 A (15 W) |
| -12 V | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) |
| Total | 149.8 W | 303.0 W | 455.3 W | 606.4 W | 749.9 W |
| % Max Load | 20.0% | 40.4% | 60.7% | 80.9% | 100.0% |
| Room Temp. | 45.5° C | 47.2° C | 47.8° C | 49.0° C | 48.3° C |
| PSU Temp. | 48.2° C | 48.5° C | 49.4° C | 51.1° C | 56.2° C |
| Voltage Stability | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Fail on -12 V |
| AC Power | 181.9 W | 356.2 W | 539.5 W | 733.0 W | 934.0 W |
| Efficiency | 82.4% | 85.1% | 84.4% | 82.7% | 80.3% |
| AC Voltage | 112.9 V | 111.2 V | 108.8 V | 106.2 V | 104.1 V |
| Power Factor | 0.991 | 0.997 | 0.998 | 0.999 | 0.998 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
Efficiency was high between 84.4% and 85.1% when we pulled between 40% and 60% from this power supply labeled capacity (i.e., between 300 W and 450 W). Under light load (20% load, i.e., 150 W) and 80% load (i.e., 600 W) efficiency dropped to between 82% and 83%, not a bad number. Under full load (750 W) efficiency dropped to 80.3%, still above the 80% mark. This unit is 80 Plus Bronze certified, meaning that according to 80 Plus organization it presents efficiency of at least 82% under full load. The difference between what we achieved and what they achieved can be easily explained: they collect data at a room temperature of only 23° C, a temperature that is impossible to be seen inside a PC, and efficiency decreases with temperature (click here for more information).
Noise level at +12V1 was very high (102.8 mV) during test five, almost touching the 120 mV limit, while -12 V output presented a 138 mV noise, surpassing the maximum allowed. All other outputs were inside the maximum allowed, but we wanted to see lower levels specially on +5 V and +5VSB, which presented 41 mV and 43.6 mV noise levels, respectively. You can see the results below for test number five. All values are peak-to-peak figures and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +5 V and +3.3 V outputs.
Figure 16: +12V1 input from load tester at 749.9 W (102.8 mV).
Figure 17: +12V2 input from load tester at 749.9 W (46.6 mV).
Figure 18: +5V rail with power supply delivering 749.9 W (41.0 mV).
Figure 19: +3.3 V rail with power supply delivering 749.9 W (25.8 mV).
Now let’s see if we could pull more than 750 W from this unit.