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Home » Power
Coolmax CUL-750B 750 W Power Supply Review
Author: Gabriel Torres
Type: Reviews Last Updated: April 16, 2010
Page: 7 of 10
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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