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TEST RESULTS
For a fuller understanding of ATX power supplies, please read our article Power
Supply Fundamentals & Recommended Units. Those who seek source materials
can find Intel's various PSU design guides, closely followed by PSU manufacturers,
at Form Factors.
For a complete rundown of testing equipment and procedures, please refer to
the article SPCR's Revised
PSU Testing System. It 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 precise 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 far too many variables in
PCs and far 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 reasonable overall representation of that person, 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
recently conducted system tests to measure the maximum power draw that an actual
system can draw under worst-case conditions. Our most powerful P4-3.2
Gaming rig drew ~180W 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 150W, but the total still remains well under 400W in
extrapolations of our real world measurements.
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 number that is comparable between different reviews, as it is unaffected
by the ambient temperature.
Because the side of the Zen is open, the top and the side of the test rig was
covered up with cardboard to simulate the walls of an actual case. This ensured
that only the rear vent is exposed to the external air, as it would be in a
real system.
Ambient conditions during testing were 25°C and 20 dBA, with
input of 120 VAC / 60 Hz measured at the AC outlet. It was a couple of degrees
warmer than usual in the lab, and the Intake Temp readings in the measured data
table below reflects this.
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FSP ZEN TEST RESULTS
|
|
DC Output (W)
|
40
|
65
|
90
|
150
|
200
|
250
|
300
|
|
AC Input (W)
|
52
|
82
|
110
|
179
|
230
|
288
|
342
|
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Efficiency
|
77%
|
80%
|
82%
|
84%
|
87%
|
87%
|
88%
|
|
Intake Temp (°C)
|
27
|
29
|
31
|
32
|
34
|
39
|
43
|
|
PSU Exhaust (°C)
|
33
|
39
|
40
|
45
|
49
|
57
|
63
|
|
Temperature Rise (°C)
|
6
|
10
|
9
|
13
|
15
|
18
|
20
|
|
Power Factor
|
0.90
|
0.93
|
0.95
|
0.98
|
0.99
|
0.99
|
0.99
|
|
NOTE: The ambient room temperature during testing
varies a few degrees from review to review. Please take this into account
when comparing PSU test data.
|
ANALYSIS
1. VOLTAGE REGULATION was excellent, within ±1% on the +12V
and +5V lines in any combination of loads. The +3.3V line strayed by a maximum
of 2%. This is very impressive performance.
-
+12V: 11.89 to 12.04
-
+5V: 4.96 to 5.00
-
+3.3V: 3.35 to 3.38
The AC power draw also remained very stable. The AC power draw for most power
supplies begins to fluctuate as it approaches full load, often by as much
as 10~20W. The Zen, on the other hand, drew exactly 342W at full load ?
no more, no less. The stability of both the AC power draw and the output voltage regulation inspires
our confidence in the quality of the design.
2. EFFICIENCY was excellent, although we did not quite reach see the claimed 89%. It is likely that this efficiency could be reached if a 240VAC
input voltage was used. Most impressive is the efficiency at low output: This
is the first power supply we have tested that measured 80% efficient at the low 65W
load. As the load increases, efficiency also goes up. Peak efficiency was achieved
at 300W output.
This performance is on par with the best we have measured: The
Antec Phantom 500. Although the Phantom is slightly more efficient under
higher loads, the Zen is more efficient below 150W ? the range in which
it is most likely to be used. These differences are minor, however, and are
always within a percentage point or two. The differences may lie within the resolution capability of our test setup.
3. POWER FACTOR was lower than we usually expect of active power factor
correction, although still very good compared to passive or no PFC. Once the
total load rose to 150W and above, power factor quickly approached the ideal
value of 1.0.
4. NOISE
The Zen is fanless, so the noise generated by the power supply was minimal.
No electrical noise was noticed during the course of the testing, which cannot
be said of some of the other fanless models on the market. There was no hum, buzz or squeal that could be heard from any distance. A trace amount of something was barely audible to Mike when he pressed his ear right up against the cover. For all practical
purposes, the Zen is silent.
5. HEAT
The temperature rise within the power supply was in line with the other fanless
power supplies we've tested. Although a 20°C rise at 300W output is hardly
stellar thermal performance for a fanned power supply, it's fairly typical for
a fanless model. Warm air could be felt coming out of the rear vent throughout
testing, which shows that there was airflow through the power supply even
though it has no active source of airflow. We can attribute most of this airflow to the internal airflow within our test
rig. The overall stability of the power supply gave us no
reason to think that its internal cooling was inadequate.
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