Enermax Tomahawk 500 W Power Supply Review

[nextpage title=”Introduction”]

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

Figure 1: Enermax Tomahawk 500 W power supply.

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:

• Main motherboard cable with a 20/24-pin connector (18 ½” or 47 cm long).
• One cable with one ATX12V connector (18 3/8” or 46 cm long).
• One cable with one six-pin video card power connector (19” or 48 cm long).
• Two cables with two SATA power connectors and one standard peripheral power connector each (19” or 48 cm to the first connector and 5 7/8” or 15 cm between connectors).
• One cable with two peripheral power connectors and one floppy disk drive power connector (19” or 48 cm to the first connector and 5 7/8” or 15 cm between connectors).

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

Figure 3: Cables.

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

[nextpage title=”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.

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, with two Y capacitors and one X capacitor more than the minimum required, plus one X capacitor after the rectifying bridge.

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 Enermax Tomahawk 500 W.

[nextpage title=”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.

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.

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).

Figure 11: Switching transistors.

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

Figure 12: PWM/PFC combo Controller.

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

[nextpage title=”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.

Figure 13: +12 V and +3.3 V rectifiers.

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.

Figure 15: Monitoring integrated circuit.

The secondary capacitors are also from Samxon.

[nextpage title=”Power Distribution”]

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

Figure 16: Power supply label.

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

• +12V1: All cables but the ATX12V connector.
• +12V2: ATX12V connector.

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.

[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 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.

Figure 17: +12VA input from load tester at 484.1 W (25.2 mV).

Figure 18: +12VB input from load tester at 484.1 W (24.2 mV).

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

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.

[nextpage title=”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

[nextpage title=”Main Specifications”]

Enermax Tomahawk 500 W power supply specs include:

• Nominal labeled power: 500 W at 40° C.
• Measured maximum power: 548.4 W at 45.6° C.
• Labeled efficiency: Information not available.
• Measured efficiency: Between 76.8% and 84.5% 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 one ATX12V connector.
• Video Card Power Connectors: One six/eight-pin connector.
• SATA Power Connectors: Four in two cables.
• Peripheral Power Connectors: Six in three cables.
• Floppy Disk Drive Power Connectors: One.
• Protections: Over voltage (OVP, not tested), under voltage (UVP, not tested), over current (OCP, not tested) and short-circuit protection (SCP, tested and working).
• Warranty: Three years
• More Information: https://www.enermaxusa.com
• Average price in the US*: USD 70.00

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

[nextpage title=”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.