OCZ ZS Series 550W Power Supply Review

1. Introduction2. OCZ SZ Series 550W (Bundle and Cables)3. OCZ SZ Series 550W (External)4. OCZ SZ Series 550W (Internal)5. OCZ SZ Series 550W (Super High Res Gallery)6. Testing Methodology and Results7. Closing Thoughts8. View All Pages

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	3.05	3.37	3.07	5.08	6.52	12.26	1.50	5.05
220W	6.24	3.35	6.21	5.07	13.51	12.21	1.50	5.04
340W	9.32	3.32	9.21	5.06	21.12	12.17	1.50	5.04
445W	12.43	3.30	12.42	5.05	27.55	12.12	1.50	5.03
550W	15.71	3.28	15.67	5.04	34.59	12.06	1.50	5.02

A fairly good set of results across the board and there are no concerns with voltage regulation.

OCZ ZS Series 550W PSU	Maximum Load
	603.5

The power supply managed to output just over 603 watts before shutting 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	3.35	1.0	5.07	40.0	11.93	0.2	-11.99	0.50	5.03
153W	15.0	3.27	15.0	4.98	2.0	12.21	0.2	-12.15	0.50	5.01

Cross loading shows minor +12V fluctuation, dropping from 12.21 to 11.93 when hit with 40 amps. Nothing to concern a prospective customer, but noticeable.

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	10	20	15
220W	10	10	25	15
340W	15	15	40	20
445W	15	15	50	20
550W	20	15	65	20

Noise suppression is within the rated tolerance parameters, although a maximum of 65 mV on the +12V output is not the best we have seen in recent months.

Efficiency (%)
110W	81.98
220W	84.77
340W	85.89
445W	84.46
550W	83.35

Efficiency from the supply is very good for a bronze rated unit, achieving almost 86% at around 50% load. It falls to 83.35% efficiency at full 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	29.8
220W	31.4
340W	33.7
445W	34.5
550W	35.9

The supply is audible at around 50% load, depending on the emissions of your partnering hardware. At full load the fan is clearly spinning fast, emitting around 36 dBa of noise.

Temperature (c)
	Intake	Exhaust
110W	36	38
220W	38	42
340W	39	47
445W	42	50
550W	43	53

The active fan helps maintain good temperature variables, rising to a 10c above ambient intake at full load.

Maximum load	Efficiency
603.5W	82.3

Pushing the PSU above its rated limits generates an efficiency level of around 82.3%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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