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Switching Power Supplies A to Z
Switching Power Supplies A to Z, by Sanjaya Maniktala (Newnes), starting at $94.17
Home » Power
Seventeam ST-750P-AF Power Supply Review
Author: Gabriel Torres
Type: Reviews Last Updated: June 30, 2009
Page: 7 of 10
Real-time pricing for XFX P1-750B-NLG9.
XFX P1750BNLG9 Pro Series XXX Edition ATX Semi-Modular Power Supply 750W 80 Plus Silver 135mm Fan Active PFC
TigerDirect: $129.99 CompUSA: $129.99

Load Tests
Hardware Secrets Golden Award

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 +12V2 rail and the +12V2 input was connected to the power supply +12V1 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

149.8 W

303.0 W

455.3 W

606.4 W

749.9 W

% Max Load

20.0%

40.4%

60.7%

80.9%

100.0%

Room Temp.

45.5º C

47.2º C

47.8º C

49.0º C

48.3º C

PSU Temp.

48.2º C

48.5º C

49.4º C

51.1º C

56.2º C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Fail on -12 V

AC Power

181.9 W

356.2 W

539.5 W

733.0 W

934.0 W

Efficiency

82.4%

85.1%

84.4%

82.7%

80.3%

AC Voltage

112.9 V

111.2 V

108.8 V

106.2 V

104.1 V

Power Factor

0.991

0.997

0.998

0.999

0.998

Final Result

Pass

Pass

Pass

Pass

Pass

Efficiency was high between 84.4% and 85.1% 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 82% and 83%, not a bad number. Under full load (750 W) efficiency dropped to 80.3%, still above the 80% mark. This unit is 80 Plus Bronze certified, meaning that according to 80 Plus organization 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 23º C, a temperature that is impossible to be seen inside a PC, and efficiency decreases with temperature (click here for more information).

Noise level at +12V1 was very high (102.8 mV) during test five, almost touching the 120 mV limit, while -12 V output presented a 138 mV noise, surpassing the maximum allowed. All other outputs were inside the maximum allowed, but we wanted to see lower levels specially on +5 V and +5VSB, which presented 41 mV and 43.6 mV noise levels, respectively. 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.

Seventeam ST-750P-AF power supply
click to enlarge
Figure 16: +12V1 input from load tester at 749.9 W (102.8 mV).

Seventeam ST-750P-AF power supply
click to enlarge
Figure 17: +12V2 input from load tester at 749.9 W (46.6 mV).

Seventeam ST-750P-AF power supply
click to enlarge
Figure 18: +5V rail with power supply delivering 749.9 W (41.0 mV).

Seventeam ST-750P-AF power supply
click to enlarge
Figure 19: +3.3 V rail with power supply delivering 749.9 W (25.8 mV).

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

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