OCZ Z Series 850 W Power Supply Review

[nextpage title=”Introduction”]

OCZ Z Series is the 80 Plus Gold-certified power supply family from OCZ, and so far they released an 850 W and a 1,000 W model. We have already reviewed the 1,000 W model, and let’s see now if the 850 W model will live up to the expectation.

Besides OCZ Z Series 1000 W, so far we’ve already reviewed two other 80 Plus Gold power supplies: Enermax MODU87+ 700 W and Seasonic X-Series 650 W.

If you read our review of the 1,000 W model you already know that both are basically the same power supply, with some components (rectifying bridges, primary capacitors and the addition of a third transistor on the active PFC circuit) upgraded on the 1,000 W model. Both models are manufactured by Highpower.

Figure 1: OCZ Z Series 850 W power supply.

Figure 2: OCZ Z Series 850 W power supply.

OCZ Z Series 850 W is relatively a short unit, being 6 ¼” (160 mm) deep, using a 135 mm fan on its bottom and active PFC circuit, of course.

Initially OCZ was going to offer two version of this power supply: with a modular cabling system and without. While some places may still have some models without the modular cabling system, OCZ won’t sell these anymore; they will be focusing exclusively on the modular cabling version.

The modular cabling system has eight connectors, with four cables permanently attached to the power supply. The cables included are:

• Main motherboard cable with a 24-pin connector (no 20-pin option), 21 ½” (55 cm) long (permanently attached to the power supply).
• One cable with two ATX12V connectors that together form one EPS12V connector, 24 3/8” (62 cm) long (permanently attached to the power supply).
• One cable with one EPS12V connector, 24 3/8” (62 cm) long (permanently attached to the power supply).
• Four cables with one six/eight-pin connector for video cards each, 23” (58.5 cm) long (modular cabling system).
• One cable with three SATA power connectors, 24 3/8” (62 cm) to the first connector, 7 ¼” (18.5 cm) between connectors (permanently attached to the power supply).
• Three cables with three SATA power connectors each, 18 7/8” (48 cm) to the first connector, 7 ½” (19 cm) between connectors (modular cabling system).
• One cable with three standard peripheral power connectors and one floppy disk drive power connector, 20 7/8” (53 cm) to the first connector, 7 ¼” (18.5 cm) between connectors (modular cabling system).

The difference between the 850 W and the 1,000 W here is the presence of two extra video card power cables (the ones permanently attached to the unit) on the 1,000 W model; the rest is identical.  This configuration is very good for an 850 W product, providing four connectors for video cards, allowing you to connect two video cards that require two power connectors each, and twelve SATA power connectors. But we think a it could have two more video power cables for users willing to walk the extra mile and build a three-way SLI system, just like the 1,000 W unit.

Figure 3: Cables.

All cables use 18 AWG wires, which is the minimum recommended, with the main motherboard cable using thicker 16 AWG wires, which is great.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The OCZ Z Series 850 W”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used. As mentioned, internally the 850 W model is practically identical to the 1,000 W model.

Figure 4: Overall look.

Figure 5: Overall look.

Figure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil. 

This power supply is flawless on this stage, two Y capacitors and one X capacitor more than the minimum required, plus one X capacitor after the rectifying bridges.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the OCZ Z Series 850 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of OCZ Z Series 850 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two TS15P05G rectifying bridges connected in parallel in its primary, each one supporting up to 15 A at 110° C. At 115 V this unit would be able to pull up to 3,450 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out. Talk about overspecification! Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply. The 1,000 W model uses two 25 A bridges here.

Figure 9: Rectifying bridges.

On the active PFC circuit two SPW24N60C3 power MOSFET transistors are used, each one capable of delivering up to 24.3 A at 25° C or 15.4 A at 100° C in continuous mode (note the difference temperature makes), or up to 72.9 A in pulse mode at 25° C. These transistors present a resistance of 160 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency. These transistors are the same ones used on the 1,000 W, but on this other model the manufacturer added a third transistor.

Figure 10: One of the active PFC transistors.

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor, manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as two or more capacitors with small capacitance are physically smaller than one capacitor with the same total capacitance. OCZ Z Series 850 W uses two 330 µF x 400 V capacitors in parallel; this is equivalent of one 660 µF x 400 V capacitor. These capacitors are Japanese, from Rubycon and labeled at 105° C, the best configuration possible. The 1,000 W model uses two 390 µF x 400 V capacitors here, also labeled at 105° C and from the same vendor.

In the switching section, another two SPW24N60C3 power MOSFETs are used on the traditional two-transistor forward configuration. The specs for these transistors are published above. These are the same transistors used on the 1,000 W model.

Figure 11: Switching transisors.

The switching transistors are controlled by the famous PFC/PWM combo controller CM6800. This was a surprise, as we didn’t expect an 80 Plus Gold using this controller, as many other manufacturers are moving to other designs in order to increase efficiency (e.g., resonant design).

Figure 12: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply is based on a DC-DC design, meaning that it is basically a +12 V power supply with the +5 V and +3.3 V outputs being generated using two separated switching power supplies connected to the +12 V rail. This design is proving to be the best choice in order to achieve high efficiency. On top of that OCZ Z Series uses a synchronous design to generate its +12 V output. In this kind of design the rectifiers are replaced with MOSFET transistors in order to increase efficiency.

Eight AP95T07GP MOSFETs are used to produce the +12 V rail, four for the direct rectification and four for the “freewheeling” part. Each one supports up to 80 A at 25° C or 70 A at 100° C in continuous mode, or up to 320 A at 25° C in pulse mode, with an RDS(on) of only 5 mΩ. This is exactly same configuration used on the 1,000 W model.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V rail is also used by the +5 V and +3.3 V rails as well; if all power was pulled from the +12 V rail alone, we are talking about a maximum theoretical current of 400 A or 4,800 W at 100° C. ¡Ay caramba!

Of course this is a theoretical number and we are just making an exercise here. The real amount of current/power each output can deliver is limited by other components.

Figure 13: +12 V transistors.

In Figure 14, you can see one of the DC-DC modules (the unit has one for the +5 V output and one for +3.3 V output). It has four IPD060N03L MOSFET transistors – each one capable of handling up to 50 A at 100° C with a 6 mΩ RDS(on) – and one APW7073 PWM controller.

Figure 14: DC-DC conversion module.

The outputs are monitored by a PS224 integrated circuit, which supports OVP (over voltage protection), UVP (under voltage protection) and OCP (over current protection). Any other protection this power supply may have is implemented outside this circuit.

Figure 15: Monitoring circuit.

All capacitors from the secondary are also Japanese, from Chemi-Con.

[nextpage title=”Power Distribution”]

In Figure 16, you can see the power supply label containing all the power specs.

Figure 16: Power supply label.

As you can see, according to the label this unit has a single +12 V rail, so there is not much to talk about here.

Now let’s see if this power supply can really deliver 850 W.

[nextpage title=”Load Tests”]

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

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for 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.

The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test both inputs were connected to the power supply single rail (+12VB input was connected to the power supply EPS12V connector and all other cables were connected to the load tester +12VA input).

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	6 A (72 W)	13 A (156 W)	20 A (240 W)	25 A (300 W)	31 A (372 W)
+12VB	6 A (72 W)	13 A (156 W)	17 A (204 W)	25 A (300 W)	31 A (372 W)
+5V	2 A (10 W)	4 A (20 W)	6 A (30 W)	8 A (40 W)	10 A (50 W)
+3.3 V	2 A (6.6 W)	4 A (13.2 W)	6 A (30 W)	8 A (26.4 W)	10 A (33 W)
+5VSB	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 W)	3 A (15 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	174.5 W	350.2 W	511.4 W	683.5 W	842.1 W
% Max Load	20.5%	41.2%	60.2%	80.4%	99.1%
Room Temp.	45.0° C	44.6° C	45.6° C	48.3° C	46.9° C
PSU Temp.	45.1° C	46.2° C	47.3° C	49.5° C	52.0° C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	198.9 W	390.7 W	573.2 W	776.0 W	971.0 W
Efficiency	87.7%	89.6%	89.2%	88.1%	86.7%
AC Voltage	115.3 V	114.3 V	112.9 V	110.7 V	108.4 V
Power Factor	0.934	0.974	0.985	0.99	0.992
Final Result	Pass	Pass	Pass	Pass	Pass

OCZ Z Series 850 W can really deliver its labeled wattage at high temperatures.

Efficiency is the highlight of this unit, as you can assume. We saw efficiency between 87.7% and 89.6% when we pulled up to 80% of its labeled wattage, i.e., up to 680 W. At full load (850 W) efficiency dropped a little bit to 86.7%, still a remarkable performance, very close to what is promised by 80 Plus Gold certification (87% at full load). As we have been exhaustively explaining in our reviews, Ecos Consulting, the company behind 80 Plus, tests power supplies at 23° C, while we test them between 45° C and 50° C, and efficiency drops with temperature. Therefore our tests are more rigorous (and more realistic) that those conducted in order to get the 80 Plus certification (click here to learn more).

Voltage regulation was very good, with all voltages within 3% of their nominal values (i.e., voltages closer to their “face value” than required by the ATX12V specification that allows a 5% tolerance for all positive voltages and 10% for -12 V). The exception was for +3.3 V during tests four and five, but still inside the 5% tolerance set by the ATX12V specification. Interesting enough we saw the exact same behavior on the 1,000 W model, so this is definitely something project-related.

Noise and ripple was always low, except on -12 V output, which was practically touching the maximum allowed at 113.4 mV. Once again we saw the exact same behavior on the 1,000 W model, so this is definitely something related to the project of these units.

 Below you can see the results for the other outputs on the same test. The maximums allowed are 120 mV for +12 V and -12 V and 50 mV for +5 V and +3.3 V. All values are peak-to-peak figures.

Figure 17: +12VA input from load tester during test five at 842.1 W (56.8 mV).

Figure 18: +12VB input from load tester during test five at 842.1 W (52.2 mV).

Figure 19: +5V rail during test five at 842.1 W (14.2 mV).

Figure 20: +3.3 V rail during test five at 842.1 W (23.4 mV).

Let’s see if we could pull even more from OCZ Z Series 850 W.

[nextpage title=”Overload Tests”]

The maximum we could pull from this power supply with it still working inside ATX12V specs can be seen below. If we increased one amp at any output noise at +12 V outputs would go above the 1
20 mV limit. During this test -12 V output was with noise above the maximum allowed at 151.2 mV.

Input	Overload Test
+12VA	32 A (384 W)
+12VB	32 A (384 W)
+5V	18 A (90 W)
+3.3 V	18 A (59.4 W)
+5VSB	3 A (15 W)
-12 V	0.5 A (6 W)
Total	929.2 W
% Max Load	109.3%
Room Temp.	38.4° C
PSU Temp.	42.8° C
AC Power	1,089 W
Efficiency	85.3%
AC Voltage	104.9 V
Power Factor	0.994

[nextpage title=”Main Specifications”]

OCZ Z Series 850 W power supply specs include:

• ATX12V 2.31
• Nominal labeled power: 850 W continuous, 940 W peak.
• Measured maximum power: 929.2 W at 38.4° C.
• Labeled efficiency: Above 90%, 80 Plus Gold certified
• Measured efficiency: Between 86.7% and 89.6% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Motherboard Power Connectors: One 24-pin connector, two ATX12V connectors that together form an EPS12V connector and one EPS12V connector.
• Video Card Power Connectors: Four six/eight-pin connectors on individual cables (modular cabling system).
• SATA Power Connectors: 12 on four cables (one cable permanently attached to the power supply and three cables on the modular cabling system).
• Peripheral Power Connectors: Three in one cable (modular cabling system).
• Floppy Disk Drive Power Connectors: One.
• Protections: Information not available. Monitoring circuit supports over voltage (OVP), under voltage (UVP) and over current (OCP) protections.
• Warranty: Five years (Power Swap)
• Real Manufacturer: Highpower
• More Information: https://www.ocztechnology.com
• Average prince in the US*: USD 200.00

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

If you are looking for an exceptional 850 W power supply, OCZ Z Series 850 W is definitely a terrific choice, especially now that OCZ dropped its price to USD 200 (USD 170 with a mail-in rebate and free shipping at Newegg.com). It competes directly with Corsair HX850W, which costs USD 190 and has comparable performance. You see, Ecos Consulting, the company behind 80 Plus, gave HX850W their Gold certification, but Corsair decided to downgrade this unit to Silver because it couldn’t deliver 87% efficiency at full load at real-world temperatures.

Corsair HX850W has some advantages over OCZ Z Series 850 W: its efficiency was a tiny bit higher when we pulled up to 60% from its labeled load (i.e., up to 510 W; OCZ model achieved efficiency a little bit higher above that) and comes with six power connectors for video cards, supporting three-way SLI, while this model from OCZ comes with the standard four connectors. On SATA connectors both models have 12, but this OCZ model has only three peripheral power connectors, while HX850W comes with another 12.

OCZ Z Series 850 W is an excellent product and the rebate and the free shipping will probably overcome these small details. Unless you really need more cables; then you will better off with HX850W.