Enermax Liberty EL500AWT & EL620AWT power supplies

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TEST RESULTS

For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to SPCR's Revised PSU Testing System, as well as SPCR's PSU Test Platform V.3 for information about efficiency testing. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

In the test rig, the ambient temperature of the PSU varies proportionately with its output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various standard loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches >40°C at full power. This is impossible to achieve with an open test bench setup.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise results obtained here still cannot be considered absolute. There are too many variables in PCs and too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you've never met. You'll probably get a pretty good overall representation, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: While our testing loads the PSU to full output (even >600W!) in order to verify the manufacturer's claims, real desktop PCs simply do not require anywhere near this level of power. The most pertinent range of DC output power is between about 65W and 250W, because it is the power range where most systems will be working most of the time. To illustrate this point, we conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most powerful Intel 670 (P4-3.8) processor rig with nVidia 6800GT video card drew ~214W DC from the power supply under full load — well within the capabilities of any modern power supply. Please follow the link provided above to see the details. It is true that very elaborate systems with SLI could draw as much as another 100W, perhaps more, but the total still remains well under 400W in extrapolations of our real world measurements.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup (a different PSU is being recorded). All other noise sources in the room were turned off while making the sound recordings.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

• Intake temperature (determined by ambient temperature and power output level)
• Efficiency of the PSU (how much heat it generates while producing the required output)
• The effectiveness of the PSU's cooling system, which is comprised of:
  • Overall mechanical and airflow design
  • Size, shape and overall surface area of heatsinks
  • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only temperature number that is comparable between different reviews, as it is unaffected by the ambient temperature.

On to the test results...

Ambient conditions during testing were 21°C and 19 dBA. The 500W and 620W models were tested separately, but, except for the efficiency tables, only the data for 500W model is shown. For lower output levels, the two models measured almost identically, typically within a single measurement unit. Differences of more than a single unit are noted in the data table.

OUTPUT & EFFICIENCY: ENERMAX LIBERTY EL500AWT 500W
DC Output Voltage (V) + Current (A)										Total DC Output	AC Input	Calculated Efficiency
+12V1		+12V2		+5V		+3.3V		-12V	+5VSB
12.23	0.97	12.22	1.74	5.18	1.00	3.42	0.00	0.1	0.2	40.4	58	69.6%
12.23	1.92	12.23	1.74	5.17	1.99	3.41	1.92	0.1	0.4	64.8	85	76.2%
12.24	1.92	12.21	3.32	5.17	2.97	3.42	1.91	0.1	0.5	89.6	114	78.6%
12.22	3.87	12.18	5.01	5.16	3.91	3.41	3.79	0.2	0.9	148.3	186/div>	81.0%
12.21	5.75	12.16	6.51	5.17	4.77	3.40	5.58	0.2	1.2	201.4	248	81.2%
12.22	6.70	12.16	8.19	5.15	6.63	3.40	6.41	0.3	1.5	248.5	308	80.7%
12.21	7.90	12.15	9.86	5.14	8.46	3.39	7.77	0.4	1.8	299.9	375	80.0%
12.22	11.67	12.14	12.77	5.13	10.24	3.39	9.53	0.5	2.4	400.5	512	78.2%
12.20	16.34	12.12	14.42	5.11	12.78	3.37	11.21	0.6	3.0	499.4	660	75.7%
NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.

OUTPUT & EFFICIENCY: EL620AWT 620W
DC Output Voltage (V) + Current (A)										Total DC Output	AC Input	Calculated Efficiency
+12V1		+12V2		+5V		+3.3V		-12V	+5VSB
12.14	0.96	12.13	1.73	5.15	1.00	3.42	0.99	0.0	0.2	42.2	60	70.3%
12.14	1.91	12.13	1.73	5.15	1.98	3.41	1.92	0.1	0.3	63.6	85	74.8%
12.13	3.85	12.13	1.73	5.15	2.96	3.41	1.93	0.1	0.4	92.7	117	79.2%
12.11	3.84	12.09	4.99	5.14	4.84	3.42	3.79	0.2	0.7	150.6	183	81.0%
12.10	5.71	12.07	6.70	5.14	4.75	3.40	5.57	0.2	1.0	200.7	246	81.6%
12.11	6.68	12.06	8.12	5.13	7.56	3.39	6.45	0.2	1.2	247.9	305	81.3%
12.09	8.74	12.04	9.62	5.12	8.47	3.38	7.75	0.3	1.5	302.2	375	80.6%
12.07	11.53	12.00	12.63	5.10	12.02	3.38	10.31	0.4	1.9	401.2	506	79.3%
12.04	16.25	11.95	14.24	5.10	14.35	3.36	12.92	0.5	2.4	500.4	647	77.3%
12.01	18.80	11.90	18.80	5.08	18.56	3.34	16.10	0.6	3.0	619.8	835	74.2%
NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.

OTHER DATA: ENERMAX LIBERTY EL500AWT 500W / EL620AWT 620W
DC Output (W)	40.4	64.8	89.6	148.3	201.4	248.5	299.9	400.5	499.4	619.8*
Intake Temp (°C)	25	26	28	32	34	35	37	40/39*	43/42*	47*
Exhaust Temp (°C)	27	30	33	37	41	43	45	49/47*	55/52*	62*
Temp Rise (°C)	2	4	5	5	7	8	8	9/8*	12/10*	15*
Fan Voltage	3.6	3.6	3.6	4.3	5.5	6.9	8.7	10.3	11.7	11.7*
SPL (dBA@1m)	21	21	21	24	30	35	38	41	44	44*
Power Factor	0.96	0.99	0.97	0.99	0.99	0.99	0.99	0.99	0.99	0.99*
NOTE: The ambient room temperature during testing can vary a few degrees from review to review. Please take this into account when comparing PSU test data. * Data in italics is for the 620W model.

ANALYSIS

The output and efficiency tables for the two samples are so close that except for the highest power measurements, they could have come from two test runs of the same power supply. For this analysis, the comments below apply generally to both samples.

1. VOLTAGE REGULATION

The samples displayed similar voltage regulation. Generally, the voltages were high, especially the +3.3V rail which was almost 4% high for much of the testing. All lines dropped by 1~2% from minimum to maximum load, so voltages actually became closer to ideal as the load increased. In all the measurements conducted, only two readings dropped below their nominal voltage values, and these were at the highest loads.

There is a small possibility that these high voltages could drop closer to nominal levels as the power supply ages, since the contact resistance of the connectors could increase due to corrosion or wear.

2. EFFICIENCY at the lowest 40W load was around 70%, but it quickly improved at higher load. By 150W output, efficiency was above 80%. Enermax claims 80% efficiency between 30-100% load, so we were able to verify the lower end of this claim. At maximum output, both samples dropped below 80% efficiency. This is very good performance.

Enermax' efficiency claim is based on an operating temperature of 0-40°C. Because the intake (ambient) temperature for loads above 400W was >40°C, the sub-80% efficiency that we measured does not technically disprove Enermax' claim. In general, most systems draw 65-200W, so typical efficiency should be around 80%.

3. POWER FACTOR was excellent thanks to the active power factor correction circuit, approaching the theoretical maximum of 1.0. Power factor is important to consider when choosing an uninterruptable power supply (UPS) because a high power factor reduces the VA required by the system. It can also reduce the AC current that is drawn by the power supply. A power supply with active power factor correction is less likely to blow a fuse when it is used on a busy household circuit.

4. TEMPERATURE AND COOLING

The internal cooling of the Liberty was adequate but not particularly special. As mentioned, the operating temperature is rated for 0-40°C, which was exceeded at >400W output in our test setup. Systems that consistently draw this amount of power require better system cooling than our PSU test box provides. However, in real usage very few systems even peak near 400W; sustaining this kind of power output in a single system is practically impossible.

400W was also the point when the airflow deflector in the 620W model began to make a difference in the internal temperatures. Above this level, the exhaust temperature of the 620W model tended to be 2-3°C cooler than the 500W model, with a corresponding decrease in thermal rise. This is not a large difference, but it is probably enough to provide the extra combined capacity that the 620W model boasts, since the thermal gap between the two models seemed to widen as load increased.

5. FAN, FAN CONTROLLER and NOISE

The noise level of the Liberty at lower loads was modest. At 21 dBA@1m, it should be quiet enough for the majority of users. The fan began to ramp up once the internal temperature hit 32°C, or 150W load in our test setup, and it became fairly noisy by the time the output was raised to 200W. This kind of behavior is still above average.

Although low in volume, the quality of the fan noise at low speeds was fairly rough. I would characterize it as a low growl. As the fan increased in speed, the growl got louder and gradually turned into a low hum. Even at higher speeds, the predominant noise was low frequency.

In a medium powered system, the Liberty may well be able to do its job without ever needing to increase the fan speed. A quiet system could be built around it. But if noise is the primary concern, there are better choices. To use the Liberty for a very quiet system, a fan swap is probably necessary.

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