[nextpage title=”Introduction”]
Enermax has just expanded their NAXN 82+ series of power supplies with the 80 Plus Bronze certification to include three new models, 450 W, 550 W, and 650 W. (This series also has 750 W and 850 W models.) However, you need to pay attention, as Enermax also has two other series called NAXN, the “plain” NAXN, also known as Tomahawk II, featuring 350 W, 450 W, and 500 W models, with no 80 Plus certification, and the NAXN 80+, featuring 350 W, 450 W, 500 W, and 600 W models, with the standard 80 Plus certification. To make things more confusing, the 550 W model that we are reviewing is sold as “NAXN” (and not “NAXN 82+”). Anyway, let’s see if this new power supply is a good pick.
Even though Enermax has its own factories, the NAXN 82+ 550 W is manufactured by a different company, CWT, which is the same company behind the NAXN 80+ models and, in fact, these new NAXN82+ models use the same platform as the NAXN 80+ models. It is important to know that the 750 W and 850 W models are manufactured by yet another company, High Power, and have a modular cabling system, a feature not available on the latest models. So, we have four different kinds of power supplies (NAXN, NAXN 80+, NAXN 82+ with modular cabling, and NAXN 82+ without modular cabling) using the same name. Some manufacturers simply can’t understand that using the same name for four different product lines is not a good marketing policy.
By the way, we’ve already reviewed the NAXN 80+ 600 W and the NAXN 82+ 750 W.
Figure 1: Enermax NAXN 82+ 550 W power supply
Figure 2: Enermax NAXN 82+ 550 W power supply
The Enermax NAXN 82+ 550 W is 5.5” (140 mm) deep, using a 120 mm sleeve bearing fan on its bottom (Yate Loon D12SH-12).
This unit doesn’t have a modular cabling system. All cables are protected with nylon sleeves, which come from inside the unit. This power supply comes with the following cables:
- Main motherboard cable with a 20/24-pin connector, 19.7” (50 cm) long
- One cable with two ATX12V connectors that together form an EPS12V connector, 23.2” (59 cm) long
- One cable with one six/eight-pin connector for video cards, 19.7” (50 cm) long
- One cable with one six-pin connector for video cards, 19.7” (50 cm) long
- One cable with three SATA power connectors and one standard peripheral power connector, 18.5” (47 cm) to the first connector, 5.9” (15 cm) between connectors
- One cable with two SATA power connectors and one standard peripheral power connector, 18.5” (47 cm) to the first connector, 5.9” (15 cm) between connectors
- One cable with two standard peripheral power connectors and one floppy disk drive power connector, 18.5” (47 cm) to the first connector, 5.9” (15 cm) between connectors
All wires are 18 AWG, which is the minimum recommended gauge.
The cable configuration is fair for a 550 W power supply, with two video card power connectors and five SATA power connectors, but we’d like to see at least one more SATA power connector available.
Figure 3: Cables
Let’s now take an in-depth look inside this power supply.
[nextpage title=”A Look Inside the Enermax NAXN 82+ 550 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.
On this page we will have an overall look, and then in the following pages we will discuss in detail the quality and ratings of the components used. The Enermax NAXN 82+ 550 W uses the same printed circuit board as the NAXN 80+ 600 W. In this review, we will be comparing the two to see what the differences are between them.
Figure 4: Top view
Figure 5: Front quarter view
Figure 6: Rear quarter view
Figure 7: The printed circuit board
[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.
In this stage, the Enermax NAXN 82+ 550 W power supply is impeccable, with two Y capacitors and one X capacitor more than the minimum required.
Figure 8: Transient filtering stage (part 1)
Figure 9: Transient filtering stage (part 2)
On the next page, we will have a more detailed discussion about the components used in the Enermax NAXN 82+ 550 W.
[nextpage title=”Primary Analysis”]
On this page we will take an in-depth look at the primary stage of the Enermax NAXN 82+ 550 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.
This power supply uses one GBU1006 rectifying bridge, which is attached to an individual heatsink. This bridge supports up to 10 A at 100° C, so in theory, you would be able to pull up to 1,115 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.
Figure 10: Rectifying bridge
The active PFC circuit uses two FDP18N50 MOSFETs, each one supporting up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (note the difference temperature makes), or 72 A at 25° C in pulse mode. These transistors present a 265 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number is, the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.
Figure 11: The active PFC transistors and diode
The output of the active PFC circuit is filtered by a 270 µF x 400 V electrolytic capacitor, from Samxon, labeled at 85° C.
In the switching section, two MDF18N50 MOSFETs are employed using the traditional two-transistor forward configuration. These transistors are similar to the ones used in the active PFC circuit, except they are from a different manufacturer. Therefore, the specifications for them were already discussed above.
Figure 12: The switching transistors
The primary is controlled by the famous CM6800 PWM/active PFC combo controller.
Figure 13: Active PFC/PWM controller
The primary of the Enermax NAXN 82+ 550 W is identical to the one from the Enermax NAXN 80+ 600 W.
Let’s now take a look at the secondary of this power supply.
[nextpage title=”Secondary Analysis”]
The Enermax NAXN 82+ 550 W uses a regular design in its secondary, with Schottky rectifiers.
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. As an exercise, we can assume a duty cycle of 30 percent.
The +12 V output uses three SBR40U60CT Schottky rectifiers (40 A, 20 A per internal diode at 100° C, 0.60 V maximum voltage drop), which gives us a maximum theoretical current of 86 A or 1,029 W for this output. The NAXN 80+ 600 W uses three 30 A rectifiers here, but the maximum theoretical current and power are the same.
The +5 V output uses one SBR30U30CT Schottky rectifier (30 A, 15 A per internal diode at 140° C, 0.54 V maximum voltage drop), which gives us a maximum theoretical current of 21 A or 107 W for this output. The NAXN 80+ 600 W uses two of these rectifiers instead of only one, thus having double the maximum theoretical current and power.
The +3.3 V output uses one STPS40L45CW Schottky rectifier (40 A, 20 A per internal diode at 130° C, 0.70 V maximum voltage drop), which gives us a maximum theoretical current of 29 A or 94 W for this output. This component is a lower voltage drop version of the one used in the NAXN 80+ 600 W.
Figure 14: The +5 V rectifier and two of the +12 V rectifiers
Figure 15: One of the +12 V rectifiers and the +3.3 V rectifier
This power supply uses an ST9S429 monitoring integrated circuit, which apparently is a rebranded S3515. This chip supports over voltage (OVP), under voltage (UDP), and over current (OCP) protections. There are two +12 V OCP channels, matching the number of +12 V rails advertised by the manufacturer.
Figure 16: Monitoring circuit
The electrolytic capacitors that filter the outputs are also from Samxon and are labeled at 105° C, as usual.
[nextpage title=”Power Distribution”]
Figure 17 shows the power supply label containing all the power specs.
Figure 17: Power supply label
This power supply has two +12 V virtual rails, as we could confirm by the presence of two “shunts” (current sensors) and the presence of two +12 V over current protection channels. Click here to understand more about this subject.
The two +12 V rails are distributed as follows:
- +12V1 (solid yellow wires): All cables, except the ATX12V/EPS12V< /li>
- +12V2 (yellow/black wires): The ATX12V/EPS12V cable
This is the typical configuration used on power supplies with two rails.
How much power can this unit really deliver? Let’s find out.
[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 the behavior of the reviewed unit 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 powers listed for each test, you may find a different value than what is posted under “Total” below. Since each output can have a slight variation (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. In 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, the +12VA input was connected to the power supply +12V1 rail, while the +12VB input was connected to the power supply +12V2 rail.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 16.5 A (198 W) | 20 A (240 W) |
| +12VB | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 16 A (192 W) | 20 A (240 W) |
| +5 V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 5 A (25 W) | 6 A (30 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 5 A (16.5 W) | 6 A (19.8 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 | 113.5 W | 215.7 W | 328.4 W | 436.4 W | 548.6 W |
| % Max Load | 20.6% | 39.2% | 59.7% | 79.3% | 99.7% |
| Room Temp. | 45.4° C | 44.8° C | 44.4° C | 44.3° C | 48.0° C |
| PSU Temp. | 50.6° C | 49.9° C | 49.9° C | 50.5° C | 52.9° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 134.5 W | 249.4 W | 381.5 W | 516.9 W | 664.0 W |
| Efficiency | 84.4% | 86.5% | 86.1% | 84.4% | 82.6% |
| AC Voltage | 118.7 V | 117.8 V | 116.5 V | 115.1 V | 113.7 V |
| Power Factor | 0.965 | 0.979 | 0.988 | 0.992 | 0.994 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
The Enermax NAXN 82+ 550 W passed our tests with flying colors.
Efficiency was between 82.6% and 86.5% during our tests. As you know, there are several power supplies with the 80 Plus Bronze certification that can’t deliver 82% efficiency at full load under high temperatures.
Voltage regulation could be a little better, but was not bad at all for an entry-level unit. In the table below, we show which outputs were outside the tighter 3% range we like to see to consider a power supply “flawless.” The outputs that were within three percent of their nominal values were labeled “≤ 3%.” All voltages were still inside the proper range. The ATX12V specification states that positive voltages must be within 5% of their nominal values, and negative voltages must be within 10% of their nominal values.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% | +11.57 V |
| +12VB | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% | +11.57 V |
| +5 V | +5.18 V | +5.17 V | ≤ 3% | ≤ 3% | ≤ 3% |
| +3.3 V | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% |
| +5VSB | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% | ≤ 3% |
| -12 V | -11.45 V | -11.52 V | -11.60 V | -11.63 V | ≤ 3% |
Let’s discuss the ripple and noise levels on the next page.
[nextpage title=”Ripple and Noise Tests”]
Voltages at the power supply outputs must be as “clean” as possible, with no noise or oscillation (also known as “ripple”). The maximum ripple and noise levels allowed are 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V, +3.3 V and +5VSB outputs. All values are peak-to-peak figures. We consider a power supply as being top-notch if it can produce half or less of the maximum allowed ripple and noise levels.
The Enermax NAXN 82+ 550 W provided very low ripple and noise levels during all tests, as you can see in the table below.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 10.2 mV | 10.4 mV | 14.0 mV | 30.4 mV | 51.2 mV |
| +12VB | 10.0 mV | 10.4 mV | 13.4 mV | 32.2 mV | 32.2 mV |
| +5 V | 8.2 mV | 8.6 mV | 10.8 mV | 12.6 mV | 15.4 mV |
| +3.3 V | 22.2 mV | 8.8 mV | 10.2 mV | 12.8 mV | 15.4 mV |
| +5VSB | 13.8 mV | 15.4 mV | 18.8 mV | 21.4 mV | 24.8 mV |
| -12 V | 12.4 mV | 14.0 mV | 16.8 mV | 20.8 mV | 28.4 mV |
Below you can see the waveforms of the outputs during test five.
Figure 18: +12VA input from load tester during test five at 548.6 W (51.2 mV)
Figure 19: +12VB input from load tester during test five at 548.6 W (32.2 mV)
Figure 20: +5V rail during test five at 548.6 W (15.4 mV)
Figure 21: +3.3 V rail during test five at 548.6 W (15.4 mV)
Let’s see if we can pull more than 550 W from this unit.
[nextpage title=”Overload Tests”]
Below you can see the maximum we could pull from this power supply. We couldn’t pull more than that because the power supply shut down, showing that its protections were working well. During this test, voltages were still within 3% of their nominal values, except at +12VA (+11.53 V) and +12VB (+11.51 V), which were still inside the proper range, though. Ripple and noise levels increased, but were still relatively low (69.2 mV at +12VA, 70.8 mV at +12VB, 21.2 mV at +5 V, and 19.4 mV at +3.3 V).
| Input | Overload Test |
| +12VA | 25 A (300 W) |
| +12VB | 25 A (300 W) |
| +5 V | 8 A (40 W) |
| +3.3 V | 8 A (26.4 W) |
| +5VSB | 3 A (15 W) |
| -12 V | 0.5 A (6 W) |
| Total | 662.4 W |
| % Max Load | 120.4% |
| Room Temp. | 47.8° C |
| PSU Temp. | 54.8° C |
| AC Power | 937 W |
| Efficiency | 79.1% |
| AC Voltage | 111.8 V |
| Power Factor | 0.995 |
[nextpage title=”Main Specifications”]
The main specifications for the Enermax NAXN 82+ 550 W power supply include:
- Standards: ATX12V 2.3
- Nominal labeled power: 550 W continuous, 605 W peak at 40° C
- Measured maximum power: 662.4 W at 47.8° C
- Labeled efficiency: Between 82% and 86%, 80 Plus Bronze certification
- Measured efficiency: Between 82.6% and 86.5%, at 115 V (nominal, see complete results for actual voltage)
- Active PFC: Yes
- Modular Cabling System: No
- Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector
- Video Card Power Connectors: One six-pin connector and one six/eight-pin connector on two cables
- SATA Power Connectors: Five on two cables
- Peripheral Power Connectors: Four on three cables
- Floppy Disk Drive Power Connectors: One
- Protections (as listed by the manufacturer): Over voltage (OVP), under voltage (UVP), over current (OCP), over power (OPP), over temperature (OTP), and short-circuit (SCP) protections
- Are the above protections really available? Yes.
- Warranty: Three years
- Real Manufacturer: CWT
- More Information: https://www.enermax.com.tw
- Average Price in the US*: USD 75.00
* Researched at Tigerdirect.com on the day we published this review.
[nextpage title=”Conclusions”]
The new Enermax NAXN 82+ 550 W provides a terrific price/performance ratio for the user who is looking for an affordable power supply with good efficiency for a mainstream PC.
During our tests, efficiency was between 82.6% and 86.5%, which is perfect for the mainstream user. As you know, there are several power supplies with the 80 Plus Bronze certification that can’t deliver 82% efficiency at full load under high temperatures. Noise and ripple levels were very low all the time. Voltage regulation could be a little better and the unit could have more SATA and peripheral power connectors, but at USD 75 we can’t complain.