OCZ ZX Series 850W Power Supply
Author: Zahn Funk
Editor: Shawn Knight
Date: 02-27-2011
Provided by: OCZ Technology
Installation / Testing

The OCZ ZX Series 850W power supply was installed with the following hardware:

AMD 1090T X6 Phenom II BE
2x2Gb Crucial Ballistix Tracer DDR3-1600
Swiftech H20-320 Edge
128Gb Crucial C300 RealSSD
Icy Dock 2.5" Adapter
1Tb WD Caviar Black
1Tb Hitachi Deskstar
LG 8x BD-RE 16x DVD-RW
ASUS EAH5870 V2 1G
Zalman VF3000A
Cooler Master HAF 932 AMD Edition

As I've often run into before, the 8pin EPS cable required an extension to reach all the way from the bottom power supply mount to the top of the case in the full tower HAF 932. None of the other cable lengths caused any problems, and all of the modular connections were easily and securely fastened, however the main ATX cable is very stiff at the motherboard end due to the capacitors and extra heatshrink used there. Another issue that concerned me is that the unit makes a very audible click/pop every time it powers off. When we conferred with OCZ about this, here's what they had to say:

    There is a NTC thermistor in the power supply to limit the surge current into the power supply during turn-on. The clicking noise is a relay that is used in parallel with the thermistor to increase efficiency once the main output of the power supply turns on. If you listen carefully it makes a noise when it turns on, relays are switches and they make noise when on or off.

Normally I associate this sort of sound with bad things when it comes to electronics, however as OCZ explains it seems it is perfectly normal. I would like to point out however that despite the reasoning, the unit does not make the same sound at turn on. Also the Sparkle Gold power supply we tested did not exhibit this symptom, and if the OCZ ZX Series uses an identical design then that further confuses the issue. Anyway as there are seemingly no other ill effects to operation, we proceed with the testing.

Using a Kill-a-Watt meter, I measured the power usage of the system at the outlet, during both idle and load. To generate the load I used OCCT's power supply test utility, which stresses both the CPU and GPU up to 100%. With AMD Cool-n-Quiet enabled, the CPU reduces clocks and voltages at idle, similar to the power saving mode of the GPU. Thus only 102W is being used when there's very little running in the system, and up to 491W at peak load. Compared to the max continuous rating that OCZ gives the ZX 850W, less than 60% is being utilized. Thus under "typical" load, the system should fall somewhere under that sweet spot of 50% where the power supply will be its most efficient.

With a Fluke digital multimeter, I also took voltage readings at the back of the connector under idle and load conditions. The +5V rail was the most stable, only varying by 0.01V between idle and load, and not budging at all when held at load. The +3.3V and +12V rails fluctuated by as much as 0.03V to 0.04V which is still within spec but not quite as stable as the PCP&C 760W or some other recently tested power supplies.

OCZ advertises the ZX Series as being 80Plus Gold certified for efficiency, which means they must meet a minimum of 87%/90%/87% efficiency at 20%/50%/100% of its rated load. According to the 80Plus.org independent report the 850W model squeaked by with an 88%/90%/87%, with an overall average efficiency of 88.62%. We have no capability of measuring this ourselves, however we can compare the ZX 850W to other 750W class power supplies tested using the identical hardware configuration. These included the PCP&C Silencer 760 (Silver), SilverStone Strider 750 (Gold), NZXT HALE90 750 (Gold) and OCZ Fatal1ty 750 (Bronze). As you can see from the graph, the ZX 850 falls inline with where it should be for a Gold rated unit, with results nearly identical to the SilverStone.

Let's wrap things up with some final thoughts and conclusion.

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