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OCZ ZX 1250W Power Supply Review

Additional technical assistance: Peter McFarland and Jeremy Price.

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
•  CSI3710A Programmable DC load (+3.3V and +5V outputs)
•  CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
330W
5.50
3.38
5.50
5.07
21.25
12.15
0.87
5.01
0.20 -12.08
620W
11.00
3.36
11.00
5.05
42.50
12.09
1.75
4.98
0.40 -12.09
918W
16.50
3.33
16.50
5.03
63.75
12.05
2.62
4.96
0.60 -12.10
1249W
9.05
3.28
9.45
4.98
95.01
11.97
3.5
4.95
0.80 -12.14
OCZ ZX 1250W
Maximum Load
1367W

We managed to get 1367W out of the unit before it would shut down via the protection circuitry. It would run happily at 1350W for some time.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
1190W 1.0 3.32 1.0 4.97 95.0 11.92 0.05 -12.18 0.05 5.01
195W 22.0 3.28 22.0 5.02 1.0 12.04 0.05 -12.15 0.05 5.00

A very good set of results, highlighting that the design can handle dramatic load changes with relative ease and well within specification.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum.

ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output
Ripple (mV p-p)
+3.3V
50
+5V
50
+12V1
120
+12V2
120
-12V
120
+5VSB
50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the OCZ unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
330W 5 5 10 5
620W 10 10 15 10
918W 10 10 20 15
1249W 15 15 30 15

Ripple suppression is fantastic and even at full load it is reading only 30mv on the +12v output. We recorded a maximum of 15mv at full load via the other minor rails. Incredible results indeed.

Efficiency (%)
330W
90.07
620W
92.32
918W
91.13
1204W
88.45

The efficiency results are fantastic, although they do fall a little short when directly compared to the Corsair AX1200W unit which we reviewed some time ago. The Corsair unit does use an LLC converter topology design however so it is understandable.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the Corsair Power Supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refridgerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
330W
28.7
620W
29.3
918W
31.5
1249W
35.7

These results are good and under most circumstances you would be hard pressed to hear the power supply, even up to 1000W load. In the upper 15% of power delivery the fan does become audible, however this would mean a power drain of 1050W or more. Not often a PC would be draining this much power at the socket.

Temperature (c)
Intake
Exhaust
330W
35
37
620W
38
43
918W
42
47
1249W
46
55

Thanks to the high levels of efficiency, the exhaust temperatures are really good, rising to a 9c above ambient under full load.

Maximum load
Efficiency
1367W
85.76%

For those interested, we measured the efficiency when stressing the unit to breaking point.over 85.76% at 1367W.

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