Load Tests

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

We tested this power supply under five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under 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.

+12V2 is the second +12V input from our load tester and during our tests it was connected to the power supply EPS12V connector, which is the only thing connected to the unit’s +12V1 rail. +12V1 is the first +12V input from our load tester and we connected the video card auxiliary power cable, the peripheral power cables and the main motherboard cable to it, so it was connected to +12V3 and +12V4 rails from the power supply.

We tried to use the same load pattern we used to test other 600 W units for a better comparison of the achieved results. We, however, had to use a different configuration for the test number 5 (100% load) because the power supply wouldn’t turn on if we configured the +12V2 input from our load tester (which was in fact connected to the power supply +12V1 rail) to pull 21.5 A like we did with other units. Since on the label was saying that each rail had a 16 A limit, this means that over current protection (OCP) was kicking in – which is great, by the way. So we had to reduce the current on +12V2 input and increase it on +12V1, which lead to a different configuration compared to tests we’ve done with other units on the 600 W range.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 4 A (48 W) 9 A (108 W) 13 A (156 W) 17.5 A (210 W) 25.5 (306 W)
+12V2 4 A (48 W) 9 A (108 W) 13 A (156 W) 17.5 A (210 W) 17.5 A (210 W)
+5V 1 A (5 W) 2 A (10 W) 4 A (20 W) 6 A (30 W) 8 A (40 W)
+3.3 V 1 A (3.3 W) 2 A (6.6 W) 4 A (13.2 W) 6 A (19.8 W) 8 A (26.4 W)
+5VSB 1 A (5 W) 1 A (5 W) 1.5 A (7.5 W) 2 A (10 W) 2.5 A (12.5 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 117.2 W 246.6 W 362.8 W 488.9 W 602.8 W
% Max Load 19.5% 41.1% 60.5% 81.5% 100.5%
Room Temp. 43.8° C 46.1° C 45.9° C 48.8° C 48.8° C
PSU Temp. 44.° C 47.5° C 46.7° C 49.4° C 49.9° C
Load Test Pass Pass Pass Pass Pass
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power (1) 135 W 278 W 415 W 569 W 720 W
Efficiency (1) 86.8% 88.7% 87.4% 85.9% 83.7%
AC Power (2) 143.9 W 293.3 W 434.1 W 597.1 W 753.0 W
Efficiency (2) 81.4% 84.1% 83.6% 81.9% 80.1%
AC Voltage 111.7 V 111.1 V 109.4 V 107.7 V 106.1 V
PF 0.987 0.995 0.997 0.998 0.998
Final Result Pass Pass Pass Pass Pass

Updated 06/24/2009: We re-tested this power supply using our new GWInstek GPM-8212 power meter, which is a precision instrument and provides accuracy of 0.2% and thus presenting the correct readings for AC power and efficiency (results marked as "2" on the table above; results marked as "1" were measured with our previous power meter from Brand Electronics, which isn’t so precise as you can see). We also added the numbers for AC voltage during our tests, an important number as efficiency is directly proportional to AC voltage (the higher AC voltage is, the higher efficiency is). Also, manufacturers usually announce efficiency at 230 V, which usually inflates efficiency numbers. We added power factor (PF) numbers as well. These numbers measure the efficiency of the power supply active PFC circuit. This number should be as close to 1 as possible. Under light load (20% load, i.e., 120 W), the active PFC circuit from this unit isn’t as good as when operating under higher loads, but 0.987 is an excellent number.

This power supply can really deliver 600 W of power at a room temperature of almost 49° C, which is great.

Zalman ZM600-HP achieves a very good efficiency if you pull between 40% and 60% from its labeled capacity (between 240 W and 360 W), around 84%. Under other loads efficiency is lower, but still above 80%.

Voltage stability was another highlight of this product, with all outputs between 3% of their nominal voltage in all tests, which is excellent (ATX standard allows voltages to be up to 5% from their nominal values and 10% in the case of the -12 V output). So voltages were always very close to their nominal values.

Noise level was also outstanding, far below the maximum allowed (120 mV peak-to-peak for 12 V outputs and 50 mV peak-to-peak for +5 V and +3.3 V outputs). Below you can see noise level for the test number five, when we were pulling 600 W from this unit.

Zalman ZM600-HPFigure 21: Noise level at +12V1 with power supply delivering 600 W (38.8 mV).

Zalman ZM600-HPFigure 22: Noise level at +12V2 with power supply delivering 600 W (51 mV).

Zalman ZM600-HPFigure 23: Noise level at +5 V with power supply delivering 600 W (26.4 mV).

Zalman ZM600-HPFigure 24: Noise level at +3.3 V with power supply delivering 600 W (26.8 mV).

Now let’s see if we could pull even more power from this unit and our tests of the power supply protections.


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.