SilverStone Element ST75EF 750 W 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 behaved 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 +12V1 and +12V2 rails and the +12V2 input was connected to the power supply +12V2 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 | 149.4 W | 301.4 W | 452.1 W | 601.5 W | 749.5 W |
| % Max Load | 19.9% | 40.2% | 60.3% | 80.2% | 99.9% |
| Room Temp. | 45.2° C | 46.5° C | 47.8° C | 46.5° C | 47.6° C |
| PSU Temp. | 47.4° C | 49.6° C | 50.8° C | 52.5° C | 55.0° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 184.1 W | 357.6 W | 540.4 W | 735.0 W | 953.0 W |
| Efficiency | 81.2% | 84.3% | 83.7% | 81.8% | 78.6% |
| AC Voltage | 111.9 V | 110.5 V | 108.2 V | 106.2 V | 103.3 V |
| Power Factor | 0.987 | 0.996 | 0.998 | 0.998 | 0.999 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
This power supply burned while delivering 750 W for a while (test five). We asked a second sample to SilverStone, which worked just fine during all our tests (we re-did the whole data collection process). So we guess we got a defective sample. Examining the burned sample, the switching transistors and the +12 V rectifiers were the components that went bad.
Efficiency was relatively high between 84.3% and 83.7% 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 81% and 82%, not a bad number. Under full load (750 W), however, efficiency dropped to 78.6%.
This unit is 80 Plus Bronze certified, meaning that according to Ecos Consulting (the company behind the 80 Plus certification) 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). This is not the first (and probably not the last) that we’ve seen a power supply passing the 80 Plus certification but failing to deliver high efficiency at higher temperatures. That is why we test power supplies at temperatures between 45° C and 50° C: they are more realistic.
One of the highlights from SilverStone Element ST75EF was voltage regulation: during our tests all outputs were within 3% from their nominal values, i.e., closer to their nominal values than required. This included the -12 V output, which usually doesn’t like to stay so close from its nominal value. Interesting enough on our test with Seventeam ST-750P-AF, -12 V output failed to be inside the correct range during test number five, so it seems that it was either a problem with the sample we got or that Seventeam fixed this problem.
Ripple and noise levels were below the maximum allowed, achieving lower values than Seventeam ST-750P-AF, so again it seems that it was either a problem with the sample we got or that Seventeam fixed this problem. 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 749.5 W (58.2 mV).
Figure 17: +12V2 input from load tester at 749.5 W (88.6 mV).
Figure 18: +5V rail with power supply delivering 749.5 W (19.6 mV).
Figure 19: +3.3 V rail with power supply delivering 749.5 W (14.4 mV).
Now let’s see if we could pull more than 750 W from this unit.