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OCZ Power Supply Roundup

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
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• 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
A
V
A
V
A
V
A
V
110W
1.02
3.34
1.02
5.03
8.04
12.07
1.00
5.03
220W
2.05
3.33
2.03
5.02
16.03
12.02
1.00
5.02
305W
3.01
3.32
3.05
5.00
22.08
11.97
1.50
5.01
410W
4.02
3.31
4.06
4.98
30.21
11.92
2.00
5.00
500W
5.03
3.30
5.08
4.96
37.35
11.85
2.50
5.00

Voltage regulation is borderline acceptable, but there is some noticeable droop on the +12V output.

OCZ CoreXStream 500W Maximum Load
515W

We managed to load the PSU with 515W watts before it shut down safely.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
493W 1.0 3.31 1.0 5.02 40.0 11.80 0.2 -12.01 0.50 5.03
153W 15.0 3.28 15.0 4.94 2.0 12.05 0.2 -12.00 0.50 5.01

The cross load test results are acceptable although the +12V output moves noticeably to 11.80V when hit with 40A.

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 unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
110W 10 15 25 15
220W 15 20 35 15
305W 15 30 50 20
410W 25 40 65 25
500W 30 45 90 25

Ripple suppression is not great, although at this very low price point we weren’t expecting to see class leading results. Still, all of the parameters fall within rated specifications.

Efficiency (%)
110W
79.4
220W
80.2
305W
82.1
410W
81.4
500W
80.1

Efficiency isn’t rating very highly either, peaking at 82.1% at 50% load.

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 Power Supply we have taken it into our acoustics room environment and have set our SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) 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)
110W
28.4
220W
29.3
305W
31.3
410W
33.6
500W 34.2

At under 300 watt load, the power supply is quiet and basically inaudible. When tasked with 500W of power, this rises to just over 34dBa. This is a quiet power supply, even when loaded high.

Temperature (c)
Intake
Exhaust
110W
35
39
220W
37
45
305W
42
52
410W
47
57
500W
50
64

The fan isn’t the highest quality unit we have tested, and the overall temperatures rise to a 14c above ambient at full load. OCZ could have adjusted the fan profile to be a little more aggressive.

Maximum load
Efficiency
515W
79.8

Pushing the PSU above its rated limits generates an efficiency level of around 79.8%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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