Nexus RX-8500 850 W Power Supply Review
By Gabriel Torres on November 25, 2009


Introduction

Hardware Secrets Silver Award

Nexus is a Dutch company and their power supplies can be easily found in the United States and in Europe, of course. We’ve already tested their 630 W model (RX-6300) and we were impressed with its performance. Is the 850 W model also a good buy? Let’s see.

This power supply is manufactured by ATNG.

Nexus RX-8500 power supply
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Figure 1: Nexus RX-8500 power supply.

Nexus RX-8500 power supply
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Figure 2: Nexus RX-8500 power supply.

Nexus RX-8500 is 6 ½” (16.5 cm) deep, using a 135 mm fan on its bottom and featuring active PFC, of course. It has a modular cabling system, but some of the cables are permanently attached to the power supply (these cables have a nylon protection that comes from inside the power supply case). Also, the modular cabling system has 10 connectors, but the power supply comes with only six cables. This power supply comes with the following cables:

The modular cabling system uses white connectors for the SATA and peripheral power cables and yellow connectors for the video card cables. If you install all cables you will still have two empty white connectors and two empty yellow connectors. This power supply supports three-way SLI, but in order to install the third video card you will need to buy the two video card connectors that are missing.

The cables that are permanently attached to the power supply are 18 1/8” (46 cm) long, and the cables from the modular cabling system are a little bit longer, with 19 ¾” (50 cm) between the power supply and the first connector on the cable. Peripheral connectors have 5 7/8” (15 cm) between them, but SATA connectors have 7 7/8” (20 cm) between them, which is great.

All cables use 18 AWG wires, which is the correct gauge to be used, with the main motherboard cable using thicker 16 AWG wires, which is terrific.

Nexus RX-8500 power supply
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Figure 3: Cables.

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

A Look Inside The Nexus RX-8500

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. The first thing we notice here is that this power supply uses two transformers. Later we will see how they are connected.

Nexus RX-8500 power supply
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Figure 4: Overall look.

Nexus RX-8500 power supply
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Figure 5: Overall look.

Nexus RX-8500 power supply
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Figure 6: Overall look.

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. 

On this power supply this stage is flawless: it has one X capacitor and two Y capacitors more than the minimum required.

Nexus RX-8500 power supply
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Figure 7: Transient filtering stage (part 1).

Nexus RX-8500 power supply
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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Nexus RX-8500.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Nexus RX-8500. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1006 rectifying bridges connected in parallel, which one supporting up to 10 A at 100° C, if a heatsink is used, which is the case (without a heatsink the current limit drops to 3.2 A). So in theory you would be able to pull up to 2,300 W from a 115 V power grid; assuming 80% efficiency, this bridge would allow this unit to deliver up to 1,840 W without burning. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Nexus RX-8500 power supply
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Figure 9: Rectifying bridge.

On the active PFC circuit three SPW20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25° C, presenting a resistance of 190 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Taiwanese from Teapo and labeled at 85° C.

In the switching section, another two SPW20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration.

Nexus RX-8500 power supply
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Figure 10: +5VSB switching transistor, two of the active PFC transistors and switching transistors.

This power supply uses the famous CM6800 active PFC/PWM combo controller.

Nexus RX-8500 power supply
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Figure 11: Active PFC/PWM combo controller.

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

Secondary Analysis

While RX-6300 (630 W) used a partial synchronous design on its secondary, RX-8500 uses a standard design with six 40CPQ045 Schottky rectifiers, each one supporting up to 40 A (20 A per internal diode at 120° C, voltage drop of 0.43 V).

As mentioned before, this power supply uses two transformers. The first transformer is used to generate half of the +12 V main rail and the +5 V output, while the second transformer is used to generate the other half of the +12 V main rail and the +3.3 V output.

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 output is produced using four of the available rectifiers, leaving us with a maximum theoretical current of 114 A or 1,371 W.

The +5 V output is produced by one the rectifiers, giving us a maximum theoretical current of 29 A or 143 W.

The +3.3 V output is produced by the last rectifiers, giving us a maximum theoretical current of 29 A or 94 W.

Nexus RX-8500 power supply
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Figure 12: Rectifiers.

The outputs are monitored by a PS232 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP) and over voltage (OVP). Any other protection that this unit may have is implemented outside this integrated circuit. As you can clearly see in Figure 13, this unit has a thermal sensor in addition to the one present on the secondary heatsink, which usually means that the power supply has over temperature protection (OTP).

Nexus RX-8500 power supply
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Figure 13: Monitoring circuit.

Electrolytic capacitors from the secondary are also Taiwanese, from Teapo and labeled at 105° C.

Power Distribution

In Figure 14, you can see the power supply label containing all the power specs.

Nexus RX-8500 power supply
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Figure 14: Power supply label.

This power supply has four virtual rails, distributed like this:

We think Nexus could at least label outside the power supply the rails each connector is attached to in order to make it easier for the advanced user to balance the load among all available rails.

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

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 +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester. During this test the +12V1 input was connected to the power supply +12V4 and +12V3 rails while the +12V2 input was connected to the power supply +12V2 rail.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12V1

6 A (72 W)

13 A (156 W)

20 A (240 W)

25 A (300 W)

31 A (372 W)

+12V2

6 A (72 W)

12 A (144 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 (19.8 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

172.8 W

347.3 W

519.1 W

697.1 W

862.4 W

% Max Load

20.3%

40.9%

61.1%

82.0%

101.5%

Room Temp.

45.8° C

45.1° C

48.8° C

47.3° C

47.5° C

PSU Temp.

47.3° C

48.1° C

51.0° C

53.1° C

53.2° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

211.1 W

410.2 W

617.7 W

847.0 W

1080.0 W

Efficiency

81.9%

84.7%

84.0%

82.3%

79.9%

AC Voltage

116.9 V

114.6 V

112.1 V

109.4 V

106.8 V

Power Factor

0.963

0.986

0.981

0.982

0.976

Final Result

Pass

Pass

Pass

Pass

Pass

Nexus RX-8500 can really deliver 850 W at very high temperatures.

Efficiency was good but not outstanding. When we pulled between 40% and 60% from the power supply maximum capacity (between 340 W and 510 W) we saw efficiency between 84% and 84.7%. At light load (20%, i.e., 170 W) and 80% load (680 W) efficiency dropped to around 82%. And at full load efficiency was just at 79.9%.

Voltage regulation was a highlight from this product, with all voltages within 3% from their nominal values, i.e., voltages close to their nominal values that what is allowed (5%). This includes the -12 V output, which usually doesn’t like to stay so close to its nominal value, except when we pulled 850 W from this power supply (but this output was still inside the valid range).

And finally we have noise and ripple, which were low all the time. Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

Nexus RX-8500 power supply
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Figure 15: +12V1 input from load tester at 862.4 W (35.2 mV).

Nexus RX-8500 power supply
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Figure 16: +12V2 input from load tester at 862.4 W (38.4 mV).

Nexus RX-8500 power supply
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Figure 17: +5V rail with power supply delivering 862.4 W (24.6 mV).

Nexus RX-8500 power supply
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Figure 18: +3.3 V rail with power supply delivering 862.4 W (25.6 mV).

Now let’s see if we could pull more than 850 W from this unit.

Overload Tests

The maximum we could pull without the power supply shutting down can be seen in the table below. Under this configuration, however, the power supply burned after working for around 2 minutes. After inspecting the power supply we saw that one of the +12 V rectifiers was the component that gave up.

Input

Maximum

+12V1

31 A (372 W)

+12V2

31 A (372 W)

+5V

20 A (100 W)

+3.3 V

20 A (66 W)

+5VSB

3 A (15 W)

-12 V

0.5 A (6 W)

Total

958.2 W

% Max Load

112.7%

Room Temp.

45.6° C

PSU Temp.

52.0° C

AC Power

1,240 W

Efficiency

77.3%

Main Specifications

Nexus RX-8500 power supply specs include:

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

Conclusions

We were a little bit disappointed with Nexus RX-8500. Since it is part of the same series as RX-6300 we expected it to achieve a higher efficiency. RX-6300 uses a partial synchronous (i.e., instead of using rectifiers on the +12 V output it uses MOSFET transistors) and this explains the better performance from this 630 W model.

But that doesn’t mean that RX-8500 is a bad product, on the contrary: it can really deliver 850 W at high temperatures, has voltages closer to their nominal values than required (3% tolerance while ATX specs allow up to 5%), presents low noise and ripple levels and is equipped with a low-noise fan. It also supports three-way SLI, but the cables for installing the third video card must be bought separately.

We think Nexus should have labeled the +12V rails outside the unit. This surely would help advanced users, since this unit has four rails and the load distribution used on this power supply is confusing.

Costing USD 150, it competes directly with Cooler Master Silent Pro M 850 W, which on our tests achieved higher efficiency and also comes with a modular cabling system supporting three-way SLI – and coming with all necessary cables. Nexus RX-8500 is certainly an option for the user looking for an honest 850 W power supply at a fair price, however we recommend you to buy Cooler Master Silent Pro M 850 W instead.

 

Originally at http://www.hardwaresecrets.com/article/Nexus-RX-8500-850-W-Power-Supply-Review/871


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