Enermax Tomahawk 500 W Power Supply Review
By Gabriel Torres on February 15, 2010


Introduction

Hardware Secrets Bronze Award

Tomahawk is an entry-level power supply series from Enermax. Let’s see if the 500 W version is a good buy.

Enermax Tomahawk 500 W power supply
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Figure 1: Enermax Tomahawk 500 W power supply.

Enermax Tomahawk 500 W power supply
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Figure 2: Enermax Tomahawk 500 W power supply.

Enermax Tomahawk 500 W is a short power supply, being only 5 ½” (140 mm) deep, using a 120 mm fan on its bottom and active PFC circuit, of course.

Being an entry-level product, it doesn’t have a modular cabling system. Only the main motherboard cable and the ATX12V cable have a nylon protection. All cables use 18 AWG wires, which is the minimum recommended. The cables included are:

This configuration clearly shows that we are dealing with an entry-level product.

Enermax Tomahawk 500 W 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 Enermax Tomahawk 500 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.

Enermax Tomahawk 500 W power supply
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Figure 4: Overall look.

Enermax Tomahawk 500 W power supply
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Figure 5: Overall look.

Enermax Tomahawk 500 W 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. 

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

Enermax Tomahawk 500 W power supply
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Figure 7: Transient filtering stage (part 1).

Enermax Tomahawk 500 W 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 Enermax Tomahawk 500 W.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Enermax Tomahawk 500 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one KBU10J rectifying bridge in its primary, which can deliver up to 10 A at 100° C if a heatsink is used or up to 8 A at 50° C if a heatsink is not installed, which is the case. At 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Enermax Tomahawk 500 W power supply
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Figure 9: Rectifying bridge.

On the active PFC circuit two STP21NM50N power MOSFET transistors are used, each one capable of delivering up to 18 A at 25° C or up to 11 A at 100° C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25° C. These transistors present a maximum resistance of 190 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.

Enermax Tomahawk 500 W power supply
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Figure 10: Active PFC transistors and diode.

This power supply uses a Chinese capacitor from Samxon labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, two STP11NK50ZFP power MOSFET transistors are used. Each of the transistors is capable of delivering up to 10 A at 25° C or 6.3 A at 100° C in continuous mode, or up to 40 A at 25° C in pulse mode, with an RDS(on) of 520 mΩ, which is very high (thus probably making the power supply to present lower efficiency).

Enermax Tomahawk 500 W power supply
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Figure 11: Switching transistors.

The primary is controlled by the omnipresent CM6800 PWM/PFC combo controller.

Enermax Tomahawk 500 W power supply
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Figure 12: PWM/PFC combo Controller.

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

Secondary Analysis

This power supply has four Schottky rectifiers on its secondary.

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 by two SBL2060CT Schottky rectifiers, each one capable of delivering up to 20 A (10 A per internal diode at 95° C with a maximum voltage drop of 0.75 V, which is a little too high – i.e., lower efficiency). This gives us a maximum theoretical current of 29 A or 343 W for the +12 V output.

The +5 V output is produced by one MBRF2545CT Schottky rectifier, which can handle up to 25 A (12.5 A per internal diode at 125° C, maximum voltage drop of 0.70 V). This gives us a maximum theoretical current of 18 A or 89 W for the +5 V output.

The +3.3 V output is produced by one STPS3045CW Schottky rectifier, which can handle up to 30 A (15 A per internal diode at 155° C, maximum voltage drop of 0.84 V). This gives a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

Enermax Tomahawk 500 W power supply
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Figure 13: +12 V and +3.3 V rectifiers.

Enermax Tomahawk 500 W power supply
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Figure 14: +5 V and +12 V rectifiers.

The outputs are monitored by an SG6516DZ integrated circuit, which supports over voltage (OVP), under voltage (UVP) and over current (OCP) protections.

Enermax Tomahawk 500 W power supply
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Figure 15: Monitoring integrated circuit.

The secondary capacitors are also from Samxon.

Power Distribution

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

Enermax Tomahawk 500 W power supply
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Figure 16: Power supply label.

This power supply has two +12 V rails, distributed like this:

This is the typical distribution used on power supplies with two +12 V rails.

Now let’s see if this power supply can really deliver 500 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 +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.

Note: We are now using the names +12VA and +12VB for the two inputs from our load tester because some people were thinking that the “+12V1” and “+12V2” names present on our table referred to the power supply rails, which is not the case.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12VA

4 A (48 W)

7 A (84 W)

11 A (132 W)

14.5 A (174 W)

17.5 A (210 W)

+12VB

3 A (36 W)

7 A (84 W)

10 A (120 W)

14 A (168 W)

17 A (204 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

6 A (30 W)

8 A (40 W)

+3.3 V

1 A (3.3 W)

2 A (6.6 W)

4 A (13.2 W)

6 A (19.8 W)

8 A (26.4 W)

+5VSB

1 A (5 W)

1 A (5 W)

1.5 A (7.5 W)

2 A (10 W)

2.5 A (12.5 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

103.4 W

194.0 W

305.6 W

397.9 W

484.1 W

% Max Load

20.7%

38.8%

61.1%

79.6%

96.8%

Room Temp.

43.1° C

42.6° C

44.6° C

47.4° C

42.6° C

PSU Temp.

48.1° C

47.8° C

48.8° C

51.0° C

51.9° C

Voltage Regulation

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

122.7 W

229.5 W

371.7 W

501.2 W

630.0 W

Efficiency

84.3%

84.5%

82.2%

79.4%

76.8%

AC Voltage

112.6 V

111.8 V

110.4 V

108.4 V

107.9 V

Power Factor

0.976

0.991

0.995

0.997

0.998

Final Result

Pass

Pass

Pass

Pass

Pass

Enermax Tomahawk 500 W can really deliver its labeled wattage at high temperatures.

Efficiency was high when we pulled between 20% and 40% from its labeled load (between 100 W and 200 W), above 84%. When we pulled 60% from its labeled load (around 300 W), efficiency was still decent at 82.2%. But pulling more than that efficiency dropped below the 80% mark.

Voltages were always inside the allowed range and noise and ripple were always below ultra low. Below you can see these levels with the power supply delivering 484.1 W (test five). The maximum allowed is 120 mV for the +12 V output and 50 mV for the +5 V and +3.3 V outputs. All numbers are peak-to-peak figures.

Enermax Tomahawk 500 W power supply
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Figure 17: +12VA input from load tester at 484.1 W (25.2 mV).

Enermax Tomahawk 500 W power supply
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Figure 18: +12VB input from load tester at 484.1 W (24.2 mV).

Enermax Tomahawk 500 W power supply
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Figure 19: +5V rail with power supply delivering 484.1 W (11 mV).

Enermax Tomahawk 500 W power supply
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Figure 20: +3.3 V rail with power supply delivering 484.1 W (14.6 mV).

Let’s see if we can pull more than 500 W from this unit.

Overload Tests

Below you can see the maximum we could pull from this unit with it still working. Above these numbers the unit would shut down, showing that its protections were working well.

Input

Overload Test

+12VA

19 A (228 W)

+12VB

19 A (228 W)

+5V

10 A (50 W)

+3.3 V

10 A (33 W)

+5VSB

3 A (15 W)

-12 V

0.5 A (6 W)

Total

548.4 W

% Max Load

109.7%

Room Temp.

45.6° C

PSU Temp.

48.2° C

AC Power

722.0 W

Efficiency

76.0%

AC Voltage

106.7 V

Power Factor

0.998

Main Specifications

Enermax Tomahawk 500 W power supply specs include:

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

Conclusions

Enermax Tomahawk 500 W is a honest entry-level power supply that will please the user building an entry-level or mainstream PC and doesn’t want to spend a lot of money on a power supply. We could pull practically 550 W from it at high temperatures and its voltages were always within the expected range and noise and ripple levels were always ultra low.

The Efficiency from this power supply is a double-edged sword. At loads up to 200 W it presented a very high efficiency for an entry-level product, above 84%. But at higher loads from 400 W on efficiency was below 80%.

OCZ StealthXStream 500 W, which is on the same price range, achieved a lower efficiency on lower loads, but higher efficiency on higher loads. Since we believe that who is buying this power supply won’t be operating it on the high-load side (especially because of the reduced number of connectors available), we can easily see Tomahawk 500 W as a better product than OCZ StealthXStream 500 W.

The “problem” is that OCZ StealthXStream 400 W – which uses a completely different internal design than its 500 W sister – is way cheaper that Tomahawk 500 W and provides high efficiency across the board, and not only at lower loads. Therefore our recommendation for users on a budget building and entry-level or mainstream PC that won’t pull a lot of power is still this 400 W model from OCZ. So unless you really need those extra 100 W – which we believe you won’t –, buy OCZ StealthXStream 400 W.

 

Originally at http://www.hardwaresecrets.com/article/Enermax-Tomahawk-500-W-Power-Supply-Review/925


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