Load Tests

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 and during all test both were connected to the single +12 V rail present on the power supply.

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 149.1 W 301.3 W 453.1 W 603.4 W 753.1 W
% Max Load 19.9% 40.2% 60.4% 80.5% 100.4%
Room Temp. 47.0° C 46.6° C 46.7° C 47.9° C 48.1° C
PSU Temp. 46.7° C 47.8° C 45.1° C 49.6° C 53.3° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Failed on +5VSB Failed on +5VSB Failed on +5VSB Pass Pass
AC Power 168.6 W 335.4 W 508.8 W 691.0 W 881.0 W
Efficiency 88.4% 89.8% 89.1% 87.3% 85.5%
AC Voltage 111.4 V 109.1 V 107.3 V 105.9 V 103.9 V
Power Factor 0.989 0.994 0.995 0.997 0.998
Final Result Pass Pass Pass Pass Pass

What efficiency! What efficiency! Corsair HX750W achieved a spectacular efficiency between 85.5% and 89.8% in our tests. Usually power supplies achieve a low efficiency when delivering their labeled power, which isn’t the case with the reviewed unit.

It is always important to remember that the 80 Plus organization is very generous on their tests: they test power supplies at a room temperature of only 23° C, which is too low. We test power supplies with a room temperature of at least the double, which we consider more realistic. Since at higher temperatures efficiency drops, this explains why we achieve lower efficiency numbers than those provided by this organization.

Even though noise and ripple levels for the main voltages were very low as we will show below, the standby (+5VSB) output had an enormous ripple level during all load patterns but tests four and five. Interesting enough we saw the same thing happening on Corsair HX850W, showing us that the problem was not with the sample we got but with the internal project. During test one ripple was at 103.4 mV, during test two it was at 134.4 mV and during test three it was at 103.8 mV. The maximum allowed is 50 mV (all values are peak-to-peak).

After this review was posted, Corsair tested this power supply using the same load patterns presented on the table above and, with a different equipment, the noise levels for +5VSB were completely different (very low). The only explanation we have is that our equipment was somehow interfering with the results. This way the comments above about the +5VSB output should not be taken at face value.

Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

Corsair HX750W power supplyFigure 17: +12V1 input from load tester at 753.1 W (39.6 mV).

Corsair HX750W power supplyFigure 18: +12V2 input from load tester at 753.1 W (43.2 mV).

Corsair HX750W power supplyFigure 19: +5V rail with power supply delivering 753.1 W (16.2 mV).

Corsair HX750W power supplyFigure 20: +3.3 V rail with power supply delivering 753.1 W (17.4 mV).

Now let’s see if we could pull more than 750 W from this unit.

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.