Zalman ZM770-XT 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.
The +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester. During this test the +12V1 input was connected to the power supply +12V3 and +12V4 rails while the +12V2 input was connected to the power supply +12V1 rail.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12V1 | 5.5 A (66 W) | 11 A (132 W) | 17 A (204 W) | 22 A (264 W) | 28 A (336 W) |
| +12V2 | 5 A (60 W) | 10.5 A (126 W) | 16 A (192 W) | 22 A (264 W) | 27.5 A (330 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 | 155.8 W | 308.3 W | 466.3 W | 617.8 W | 773.8 W |
| % Max Load | 20.2% | 40.0% | 60.6% | 80.2% | 100.5% |
| Room Temp. | 47.7° C | 46.9° C | 48.3° C | 47.2° C | 49.6° C |
| PSU Temp. | 44.2° C | 45.3° C | 47.0° C | 49.6° C | 53.2° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 187.3 W | 361.7 W | 550.1 W | 742.0 W | 961.0 W |
| Efficiency | 83.2% | 85.2% | 84.8% | 83.3% | 80.5% |
| AC Voltage | 114.2 V | 112.2 V | 110.4 V | 108.2 V | 105.8 V |
| Power Factor | 0.936 | 0.970 | 0.981 | 0.981 | 0.962 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
Zalman ZM770-XT can really deliver its labeled wattage at high temperatures.
Efficiency was high when we pulled between 40% and 60% from its labeled wattage (i.e., between 308 W and 462 W), being between 84.8% and 85.2%. At light load (20% load, i.e., 154 W) and 80% load (i.e., 616 W) efficiency was still pretty good at 83%. At full load (770 W) efficiency dropped to 80.5%, still above the 80% mark.
This unit is 80 Plus Bronze certified, meaning that it should present 82% efficiency at full load. This didn’t happen because differently from Ecos Consulting we test power supplies at high temperatures, and efficiency drops with temperature (read our Can We Trust the 80 Plus Certification? article for more details).
Voltage regulation was the highlight from this power supply. All voltages stayed at a maximum of 3% from their nominal values (i.e., voltages closer to their official values than required, since the ATX specification allows them to be up to 5% from their nominal values (10% for the -12 V). This included the -12 V output, which usually doesn’t like to stay at such tight tolerance.
Noise and ripple were inside the allowed range (maximum of 120 mV for the +12 V outputs and 50 mV for the +5 V and +3.3 V outputs, peak-to-peak figures), however the -12 V output was touching its limit at 115.4 mV during test five.
Figure 14: +12V1 input from load tester at 773.8 W (73.4 mV).
Figure 15: +12V2 input from load tester at 773.8 W (86.6 mV).
Figure 16: +5V rail with power supply delivering 773.8 W (24.4 mV).
Figure 17: +3.3 V rail with power supply delivering 773.8 W (28.6 mV).
Let’s see if we can pull more power from Zalman ZM770-XT.