Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 1

Around 2 months ago I took a look at the Silverstone Zeus 750w ST75ZF, and was so impressed with the overall quality and stability of the unit that I gave it a total score of 9/10 and the highly regarded 'Editors Choice' Award.

Since then, Silverstone have been hard at work producing an even more powerful 850w unit, which not only has quad +12v rails, but also fully integrated quad PCI-E connectors to boot.

Will this latest unit further strengthen the excellent reputation of the Zeus series? We find out...


Continuing the trend of all previously reviewed Silverstone power supplies, the ST85ZF is packaged in a large black and blue box bearing the Silverstone logo along with a picture of the unit.

ST85ZF Box ST85ZF Box

Silverstone have updated their packaging slightly with the inclusion of ROHS stamp which came into force on the 1st July 2006. We can also see that the front and top of the packaging offer some basic specifications along with some images of the unit and the rated output of the units rails.

ST85ZF Box ST85ZF Box

Turn the box around to the side, and we can see some of the 'Special Features' of the Silverstone unit. The ST85ZF boasts 6 SATA connectors, 4 PCI-E connectors, a maximum efficiency of 87% and multiple over-load/volt protection features.

A handy feature of the packaging is the plastic handle on the top of the box, which will certainly make carrying this unit home from the shops a much easier task.

ST85ZF Packaging ST85ZF Packaging

Included in the package are the following items:

- 1x 8-Pin AUX to 4-Pin P4-12v Adapter
- 1x Power cable
- 1x ST85ZF Manual
- 4x ATX Screws
- 1x Silverstone ST85ZF PSU

The unit itself is sandwiched in-between two cardboard layers, each padded out with Styrofoam shapes to protect all corners of the PSU. Also included is a small cardboard box containing the power cord, screws, 8-pin and 4-pin P4-12v converter. The bundle of cables are contained within a bubble-wrap sleeve and tied together with a large cable-tie.

Having a quick flick through the ST85ZF manual I can see that Silverstone have provided detailed information regarding the +12v rail layout of the unit. However, there's an easier way to find out this information, which can be seen on the 'Connectors' page.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 2

- Quad +12V rail for superior performance (70A combined)
- Quad PCI-E 6pin connectors
- Industrial class components
- Support for ATX 12V 2.2 & EPS12V
- Active PFC
- Efficiency greater than 80% (max. 87%)

ST85ZF Specs

The following rail layout information has been taken from the Silverstone manual:

24-Pin ATX Connector = +12v3
Molex+Floppy = +12v3
Serial ATA = +12v2
EPS-12v (8-Pin) = +12v1/+12v2
EPS-12v (6-Pin) = +12v3
PCI-E #1 & #2 = +12v4
PCI-E #3 = +12v2
PCI-E #4 = +12v3

With 22amps on each of the +12v rails this power supply should have no problems what so ever running any kind of SLI/Crossfire setup, and should be well equipped for a 7950GTX Quad-SLI setup too.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 3

The ST85ZF shares exactly the same dimensions as its brother the ST75ZF, coming in at 150 mm (W) x 86 mm (H) x 180 mm (D). This is a pleasant surprise that Silverstone managed to pack an extra 100w into the unit without the need to make it any bigger.

ST85ZF Front ST857F Back

Silverstone seem to have a tradition of keeping their power supplies very plain, and only spraying them in matt black paint. This is certainly true of the ST85ZF which is very similar in appearance to the ST75ZF.

The back of the power supply has the usual mesh grill, which allows for the air pushed over components by the 80mm fan to exit the back of your PC case. Also included is an LED which shows you the current status of the unit. When switching the Power Supply on the LED turns from Red to Green. Only when the LED is Green is DC power supplied to the rails.

It's good to see that Silverstone have opted for a black fan grill on the front of the unit, as the silver one used on the ST75ZF looked somewhat out of place.

ST85ZF Side ST85ZF Side

The sides of the unit have also been kept very simple, with only a specification sticker containing the usual warnings and information about the power supply, along with its rated output for all of the rails.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 4

In previous reviews, Silverstone Zeus power supplies have been well equipped with connectors and only let down by the lack of sleeving on the SATA/Molex cables. Let's see if the ST85ZF is any different...

ST85ZF Cables ST85ZF Cables

ST85ZF Cables ST85ZF Cables

The Zeus comes complete with a big bundle of cables, all wrapped together inside a bubble wrap bag and secured with a cable tie.

The Molex and SATA connectors have been sleeved up to the first connector, which is an improvement over the ST75ZF that left these cables unsleeved. It would have been nice for all cabes to be completely sleeved, but this would serve no practical purpose other than looks.

The overal quality of the sleeving job is excellent, using both cable ties and heat shrink to hold the sleeving in place.

ST85ZF Cables ST85ZF Cables

Credit has to be given to Silverstone for labelling all connectors with the corresponding rail that they obtain their +12v power from. As we can see from above, the Molex connectors obtain their 12v power from the +12v3 rail, and one of the PCI-E connectors obtains its power from +12v4.

This is especially helpful for ensuring that you distribute the load used by your components amongst the 4 available +12v rails.

ST85ZF Cables ST85ZF Cables

ST85ZF Cables ST85ZF Cables

The ATX Connector is native 24-pin. Unlike other power supplies, it doesn't have a 4-pin block which can be snapped off for backwards compatibility with older motherboards. Users of the older 20-Pin ATX motherboards will have to purchase a converter in order to use this power supply.

The ST85ZF is also native EPS-12v, providing the user with an 8-Pin connector. However, Silverstone have included an extension cable, which coverts the connector to 4-Pin ATX-12v.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 5
Looking Inside

As with all power supplies that pass through Overclock3D, I'll be taking a look inside the Zeus. By doing this I should be able to get a good idea of the overall build quality of the unit and how it is likely to perform in our tests.

It will also be interesting to see exactly what has changed between the ST75ZF and ST85ZF models.

ST85ZF Inside ST85ZF Inside

ST85ZF Inside ST85ZF Inside

The ST85ZF utilises 2 circuit boards placed at the top and bottom of the casing in order to fit all of the components inside the unit.

We can see from above the internals of the ST85ZF are manufactured by Etasis, a well respected industrial power supply manufacturer. Those of us 'on the ball' will also notice that the circuit board used in this power supply is exactly the same model as that used in the 750w ST75ZF version.

SZ85ZF Internals ST85ZF Internals

So what makes the ST85ZF 850w if it has the same circuit boards as the 750w ST75ZF model? Well basically, upgraded components...

As you can see above many of the components placed inside the unit are labelled EPAP-850. These components are what gives the unit the extra 100w advantage over its brother the ST75ZF.

ST85ZF Adjustable Pot

Above we can see what appears to be an adjustable potentiometer (pot). This will most likely be responsible for adjusting the voltages on the rails of the unit and can be helpful when voltage levels fall outside of ATX specifications. Unfortunately I was unable to test whether this pot made any difference to the voltages, as the ST85ZF is far too awkward to disassemble and reassemble.

EDIT 01/08: Silverstone have informed us that this potentiometer is not responsible for adjusting the voltages. All voltages are set at the factory and should not need adjusting.

ST85ZF Fan

Cooling the Zeus is an 80mm fan manufactured by Sanyo Denki. The San Cooler 80 is able to push a total of 42cfm when running at 12v, with a noise output level of 34dBA.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 6
Load Testing

In order for the results from all current and future PSU reviews to remain fair and comparable, Overclock3D uses a custom built Power Supply load stress tester.

The tester will be placing the following loads on each of the ST85ZF's rails:

+3.3v - 20a Load
+5.0v - 20a Load
+12v1 - 10a Load
+12v2 - 10a Load
+12v3 - 10a Load
+12v4 - 10a Load

The results are collected from a Mastech MAS-345 Multimeter which logs its readings via RS232 to a PC.

ST85ZF +3.3v Rail ST85ZF +5v Rail

The ST85ZF has some of the most stable +3.3v and +5v rails we've ever tested at OC3D to date. With little to no fluctuation, this brings the ST85ZF in direct competition with the recently reviewed PC Power & Cooling 1kw PSU.

ST85ZF +12v1 ST85ZF +12v2

ST85ZF +12v3 ST85ZF +12v4

Continuing the trend on the +12v rails, the ST85ZF breezes through our stress testing with a maximum of 0.4% fluctuation on the rails. Yet again, these results place the ST85ZF up against some of the best power supplies we've ever tester here at Overclock3D.

Efficiency Testing

Efficiency tests are performed by measuring the wattage consumed by the power supply at the mains against the power (in watts) consumed by the OC3D power supply stress tester.

The results may not be as accurate as those produced by professional testing equipment, but will certainly come in handy when comparing several power supplies against each other.

ST85ZF Efficiency

The Silverstone Zeus 850w was placed under a load of 646 watts. This counts for a total of 76% of the power supplies rated output. At this load, the power supply required 786 watts from the mains to produce the 646 watts required by our custom made power supply tester.

Therefore the efficiency of this power supply can be found by a simple equation: (646 / 786) * 100 that works out to be an efficiency rating of 82.1%.

Noise Testing

At present Overclock3D doesn't have the professional equipment required to reliably measure the noise output of devices. However, as a new part of our testing procedure we will be recording the PSU at idle and load so that you can make your own judgments. All recordings are taken at 30cm distance from the unit.

Idle Recording - Download
Load Recording - Download

As previously stated, the ST85ZF utilises a Sanyo Denki San Cooler 80mm fan, which pushes a 42cfm at 34dBA when running at full speed. Thankfully Silverstone have implemented a fan speed controller that adjusts the RPM based on the temperature of the unit.

Under idle conditions the fan speed was significantly throttled. This meant that all that could be heard was the whisper of air moving around the unit. With the ST85ZF installed inside a case, I was unable to hear the unit at all.

When placed under load, the ST85ZF gradually increased the fan speed to counteract the heat. As you can hear from the recording above, the ST85ZF was quite noisy. However, with the ST85ZF installed inside a case, the noise levels were much more reasonable.

Silverstone Zeus 850w ST85ZF Quad SLI PSU Page: 7

The Silverstone Zeus 850w has some of the most stable rails on any power supply we've tested to date. With less than 0.5% voltage fluctuation on all of the rails, this brings the ST85ZF in direct competition with some of the biggest names in the power supply market.

Combine this with a good efficiency level of around 82%, native Quad-SLI cabling, a retail price of £175 over at and the ST85ZF is a serious contender for that high-end, power hungry PC.

+ Excellent rail stability (less than 0.5% fluctuation)
+ Good efficiency (82%)
+ Fully Quad-SLI Compatible
+ Plenty of cables
+ Competitive pricing
+ Rail information printed on cables

- Slightly noisy under full load

Editors Choice

Thanks to Silverstone for providing this unit for review.

Discuss this review in our forums.