Coolmax CUL-750B 750 W Power Supply Review

Load Tests

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.  

In our tests we connect the power supply being tested inside our thermal chamber and leave it there running with a load representing 60% of the power supply capacity until the temperature inside the chamber has increased to around 47° C. The first sample we’ve got from this unit burned after only a few minutes under this condition, not allowing us to even test it. We replaced the defective unit with the store we bought it from and, because what happened with the first sample, we decide to increase load little by little until we could see the maximum amount of power we could extract from the reviewed unit.

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 +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test both inputs were connected to the power supply single rail.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 3 A (36 W) 3.5 A (42 W) 4.5 A (54 W) 5.5 A (66 W) 6.25 A (75 W)
+12VB 2.5 A (30 W) 3.25 A (39 W) 4 A (48 W) 5 A (60 W) 6 A (72 W)
+5V 1 A (5 W) 1 A (5 W) 1.5 A (7.5 A) 1.5 A (7.5 A) 2 A (10 W)
+3.3 V 1 A (5 W) 1 A (5 W) 1.5 A (4.95 W) 1.5 A (4.95 W) 2 A (6.6 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 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 87.3 W 102.6 W 128.5 W 152.8 W 178.4 W
% Max Load 11.6% 13.7% 17.1% 20.4% 23.8%
Room Temp. 40.8° C 40.7° C 41.2° C 41.8° C 43.3° C
PSU Temp. 46.5° C 46.3° C 46.5° C 47.0° C 47.9° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 107.3 W 124.3 W 153.2 W 181.4 W 211.1 W
Efficiency 81.4% 82.5% 83.9% 84.2% 84.5%
AC Voltage 114.6 V 114.4 V 114.1 V 113.8 V 113.0 V
Power Factor 0.977 0.978 0.982 0.986 0.989
Final Result Pass Pass Pass Pass Pass
Input Test 6 Test 7 Test 8 Test 9 Test 10
+12VA 7.5 A (90 W) 8.25 A (99 W) 9.25 A (111 W) 10 A (120 W) 11 A (132 W)
+12VB 7 A (84 W) 8 A (96 W) 9 A (108 W) 10 A (120 W) 11 A (132 W)
+5V 2 A (10 W) 2.5 A (12.5 W) 2.5 A (12.5 W) 3 A (15 W) 3 A (15 W)
+3.3 V 2 A (6.6 W) 2.5 A (8.25 W) 2.5 A (8.25 W) 3 A (9.9 W) 3 A (9.9 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 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 205.9 W 230.5 W 254.8 W 279.9 W 303.8 W
% Max Load 27.5% 30.7% 34.0% 37.3% 40.5%
Room Temp. 44.3° C 45.3° C 46.6° C 48.0° C 43.4° C
PSU Temp. 48.6° C 49.9° C 41.6° C 53.3° C 44.9° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 242.4 W 272.7 W 301.3 W 332.3 W 360.8 W
Efficiency 84.9% 84.5% 84.6% 84.2% 84.2%
AC Voltage 112.5 V 113.2 V 112.7 V 111.9 V 108.8 V
Power Factor 0.992 0.994 0.995 0.996 0.996
Final Result Pass Pass Pass Pass Pass
Input Test 11 Test 12 Test 13 Test 14 Test 15
+12VA 12 A (144 W) 13 A (156 W) 14 A (168 W) 15 A (180 W) 16 A (192 W)
+12VB 11.75 A (141 W) 12.75 A (153 W) 13.5 A (162 W) 14.5 A (174 W) 15.5 A (186 W)
+5V 3.5 A (17.5 W) 3.5 A (17.5 W) 4 A (20 W) 4 A (20 W) 4.5 A (22.5 W)
+3.3 V 3.5 A (11.55 W) 3.5 A (11.55 W) 4 A (13.2 W) 4 A (13.2 W) 4.5 A (14.85 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 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 328.2 W 351.8 W 377.4 W 400.4 W 428.9 W
% Max Load 43.8% 46.9% 50.3% 53.4% 57.2%
Room Temp. 46.2° C 48.8° C 45.6° C 49.4° C 44.4° C
PSU Temp. 48.2° C 52.0° C 48.2° C 53.2° C 46.4° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 392.6 W 422.5 W 454.1 W 485.9 W 521.4 W
Efficiency 83.6% 83.3% 83.1% 82.4% 82.3%
AC Voltage 108.4 V 108.3 V 107.9 V 107.9 V 107.5 V
Power Factor 0.996 0.996 0.996 0.997 0.996
Final Result Pass Pass Pass Pass Pass
Input Test 16 Test 17 Test 18
+12VA 17 A (204 W) 18 A (216 W) 19 A (228 W)
+12VB 16.5 A (198 W) 17.25 A (207 W) 18.5 A (222 W)
+5V 4.5 A (22.5 W) 5 A (25 W) 5 A (25 W)
+3.3 V 4.5 A (14.85 W) 5 A (16.5 W) 5 A (16.5 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 451.6 W 476.8 W Fail
% Max Load 60.2% 63.6% Fail
Room Temp. 48.0° C 49.4° C Fail
PSU Temp. 39.4° C 40.5° C Fail
Voltage Regulation Pass Pass Fail
Ripple and Noise Pass Pass Fail
AC Power 554.0 W 590.0 W Fail
Efficiency 81.5% 80.8% Fail
AC Voltage 106.8 V 106.6 V Fail
Power Factor 0.997 0.996 Fail
Final Result Pass Pass Fail

Coolmax CUL-750B 750 W burned while we tried to pull 500 W from it at high temperatures. It burned exactly on the same point our first sample burned. The components that burned were one of the switching transistors and one of the +12 V rectifiers. Therefore, this unit shouldn’t be labeled as a 750 W unit, but as 475 W instead. Note that this unit has no protections to prevent it from burning. On next page we will show you the video from this power supply burning when delivering 500 W.

Efficiency was always above 80%, peaking 84.9% when we pulled around 200 W from it. Voltages were always within the allowed range and noise and ripple were always low. For instance, during test 18, with the unit delivering 500 W and before it burned noise level on +12VA was at 47.6 mV, on +12VB was at 51.4 mV, on +5 V was at 38.2 mV and on +3.3 V was at 37.4 mV. The maximum allowed is 120 mV on +12 V outputs and 50 mV on +3.3 V and +5 V outputs. All numbers are peak-to-peak figures.

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Author: Gabriel Torres

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.

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