Mushkin XP-650 power supply

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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 PSU Test Platform V.3. 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 under 400W in extrapolations of our real world measurements.

SPCR's revised 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 one meter and 30cm from the exhaust vent at a 45° angle, outside the airflow turbulence area. 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 PSU 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 25°C and 19 dBA, 121V/60Hz.

OUTPUT & EFFICIENCY: Mushkin XP-650
DC Output Voltage (V) + Current (A)
Total DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.10
0.96
12.08
1.72
5.08
0.98
3.40
0.96
0.0
0.2
41.6
77
54.3%
12.08
1.90
12.08
1.72
5.07
1.95
3.39
2.81
0.1
0.3
65.8
105
62.5%
12.09
1.89
12.06
3.44
5.07
2.89
3.39
2.77
0.1
0.4
91.6
135
67.8%
12.08
3.80
12.04
4.94
5.07
4.72
3.38
4.65
0.1
0.7
149.7
202
74.1%
12.05
10.52
11.97
9.54
5.04
8.96
3.35
8.44
0.3
1.5
325.5
436
74.7%
11.99
21.20
11.83
18.56
4.99
20.40
3.30
16.32
0.5
3.0
650.4
923
70.5%
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 SUMMARY: Mushkin XP-650
DC Output (W)
41.6
65.8
91.6
149.7
325.5
650.4
Intake Temp (°C)
27
29
31
34
43
52
Exhaust Temp (°C)
30
33
35
40
51
67
Temp Rise (°C)
3
4
4
6
8
15
Fan Voltage (V)
6.4
6.4
6.4
6.5
9.2
10.9
SPL (dBA@1m)
36
36
36
36
44
48
Power Factor
0.61
0.63
0.64
0.66
0.71
0.73
AC Power on Standby: 3.0W / 0.30 PF
AC Power with No Load, PSU power On: 25.3W / 0.55 PF
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.

ANALYSIS

Regular readers will notice that our usual practice of taking measurements at many incremental power output points above 150W was not followed. There's a simple reason. (We're going to give away our conclusions right here.) This power supply is too loud under any load to be suitable for a quiet computer, and it is too inefficient and expensive for it to be a good candidate for modification. It crosses our ~30 dBA@1m "quiet enough" line as soon as it's turned on by some 5 dBA. Given these findings — which we came to as soon as we powered the unit up and listened for a minute, then confirmed with the first sound level meter reading at minimum load — there was little point to spending time and effort documenting all the ways in which the unit is too loud and too inefficient.

Let's put it this way: We've never reviewed a power supply that started louder, and the very first computer power supply we tested nearly five years ago (a Seasonic) would kill it for acoustics and match it for efficiency.

1. LOW LOAD PERFORMANCE

Power consumption in standby mode was low, coming in at ~3W and a power factor of 0.30. There was an oddity in standby: With any load on the +5V standby line, the unit emitted a high pitch whine. With about 0.5A on +5VSB, the whine was actually loud enough to be measured: 23 dBA@1m. It sounded very nasty.

The power supply would start even with no load applied. Note, however, that when powered up with no load, the power consumed was a very high 25.3W, which implies a fairly large dummy resistor load to ensure consistent starts with the wide variety of system loads that a computer power supply might see in this day and age.

2. VOLTAGE REGULATION was excellent, staying within about 1% for all lines at all test loads.

3. EFFICIENCY was poor for a high end power supply. At 50% load (325W) it reached just 74.7%. It is possible that somewhere between 50% and 100% load, a higher efficiency could be achieved, but we doubt it would be much higher than perhaps 76%. It did meet the claimed 70~73% efficiency at full load. At the more important lower loads where most PC systems idle much of the time, efficiency was very poor, just barely breaking 60% at 65W and staying below 70% until over 100W output.

4. POWER FACTOR was mediocre, about average for a passive PFC or no PF design.

5. TEMPERATURE & COOLING

Cooling was pretty good. The temperature rise stayed modest to 50%. It hit +15°C at maximum power, which is a bit high, but it's so unlikely to reach such a load sustained in real use that this is almost irrelevant.

6. FAN, FAN CONTROLLER and NOISE

The noise emitted by the unit upon turn on at any load was 35~36 dBA@1m. This is unacceptably loud by SPCR standards, and it would be plainly audible in most enviroments, be it home or office. The quality of the noise was not pleasant, either, but at this high a level, it's a moot point. Thankfully, it didn't get any louder up to 150W load, but this is also moot, as it was already too loud. By 50% load, it was at a nerve-racking 44 dBA@1m. Chances are, the high fan speed (and resulting loud noise) was dictated by the cooling needs of this relatively inefficient, high power PSU. Still, this may be perfectly accepatble for gamers who play with speakers or headphones at full blast.

The decibel and fan speed numbers cited in the manual are so different from our findings that they might as well be referring to a different model: "22-24 dBA, 490~550rpm up to 60% load; 27-30 dBA, 1590-1830rpm under full load." We could not measure fan RPM, but at no point did they sound anywhere remotely close to being under 1000rpm or 30 dBA@1m.



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