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CoolerMaster Silent Pro M2 720W PSU

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A Silent Pro M 700W power supply has been doing reliable yeoman duty in SPCR labs for years. We examine a new variant, the CoolerMaster Silent Pro M2 720W out of curiosity and not a little hope for more of the same.

Product
Silent Pro M2 720W

RS-720-SPM2
ATX12V power supply
Manufacturer
CoolerMaster
Street Price
US$100~125

Long time readers of SPCR probably know that we’ve been using a CoolerMaster
Silent Pro M 700W
PSU for umpteen case reviews (and other assorted duties
in our lab) for a long time. Our reasons for keeping the same test component
for as long as possible is not about penny pinching but maintaining consistency
over time, so that today’s reviews can be easily and confidently compared to
those done even years ago . As a result, our 3+ year old Silent Pro M 700W sample
has taken quite a beating; remember that PC component makers do not really expect
their products to be installed and uninstalled more than a few times. (Some
long time readers might recall that we once quoted Intel saying that a CPU socket
on a motherboard was not really intended to be used more than around 20 times.)
Enough digression: Our old Silent Pro M just keeps on trucking through all the
abuse, so we were curious about the newer Silent Pro M2 series. Hence this review.

There are six other models in the Silent Pro M2 series, and the 720W sits smack
in the middle: 420W, 520W, 620W, and 850W, 1000W, and 1500W are the ratings
of the other models. Five models in the original M series are still available.
As long as we’re counting, the brand actually offers a total of some 54 models,
at least by my quick count on
this CoolerMaster page
. I could repeat what I’ve written in previous PSU
reviews — that it is an incredibly large number of models, especially when
some of them are only 100W apart — but it’s not so incredible when you
discover that most "serious" PSU brands offer similar numbers of models.

Unlike many of the PSUs I’ve tested recently, the Silent Pro M2 700W is not
a super-high efficient model. It sports an 80 PLUS Bronze tag, which only requires
minimum efficiency of 85% at mid-load, and 82% at full load and 20% load. By
current standards, it’s not a champ but a footman. Still, for a 720W Bronze
unit, its typical pricing of $120 or more is on the higher side.


Full color retail package.



No fancy velour bag for the PSU nor pouches for the cables, just the basic
gear: AC and output cables, screws, and an intruction sheet.

DETAILS

The Silent Pro M2 720W is nicely finished in black, with white and grey logo
lettering. A 135mm fan with 11 blades is employed behind a wire ring intake,
and the exhaust vent is a typical hex pattern grill.


The PSU looks sturdy, fairly typical, with a 135mm 11-fin fan. Only the
main ATX and 4+4 pin AUX12V cables are attached, and they are sleeved,
unlike the flat data-style detachable cables.


On the output side, there are two outputs for PCIe power and five outputs
for peripherals. As usual, the locking output connectors are keyed to
prevent user error.

CoolerMaster Silent Pro M2 720W HIGHLIGHTS
FEATURE & BRIEF Our comment
Copper-Aluminum Heat Sink
An expansive flat surface area for superior heat conductivity out to the
aero-dynamic fins, therefore removing heat at an unprecedented rate.
OK
ErP Lot 6 ready!
Help system meet ErP Lot 6 2010 (< 1W at standby mode) with high efficiency
+5Vsb circuitry.*
We’ve seen <1W in standby with lots
of PSUs
Intel Compliant
Proficiently prepared to provide a stable power source and connectors for
the latest ATX 12V v2.3 Intel processors.
OK.
Single 12V Power Rail
Tackling challenges from the most power-intensive peripherals head on, this
solitary 12V power rail provides ample power and strong resistance to any
overloading up to 58A.
OK
Modularized Cabling
Neatly arranged connectors on the rear plate connect to flat internal cabling
improve installment facility while allowing for greater airflow through
the PSU.
OK
Eco-friendly design: Erp Lot6
Ready!

A maximum 5Vsb current draw target in S5 off-mode of 0.1A for its motherboards
and needed to ensure the system will consume < 1W in its off-mode
OK
Silent Operation
135 mm Hydraulic Dynamic Bearing Fan for quieter operation
OK
Operating Temperature: 0~40°C OK
Safety certifications:
TUV / CE / UL / FCC / BSMI / GOST / C-tick / KC / CCC
As expected.
Multiple Protection Design:
OVP/UVP/OPP/OTP/SCP
OK
Universal AC Input (90-264
VAC) with Active PFC
Like most high end PSUs .
5 year warranty Great!
150 x 180 x 86mm
5.9 x 7.1 x 3.4 inch
Much bigger than standard
ATX; probably used for higher power models as well.
CoolerMaster Silent Pro M2 720W SPECIFICATIONS
AC Input
90~264VAC, 11~5.5A, 50/60Hz
DC Output
3.3V
5V
12V1
-12V
5Vsb
20A
25A
25A
0.3A
2.5A
150W
696W
3.6W
12.5W
720W

The 40°C upper operating temperature limit (for rated performance)
is 10°C lower than some others, but in actual use, it will not be a factor.
The -12V line rating is a bit lower than most, but again, in actual use, it
will not be significant. About the most significant aspect of the specs are
the dimensions; 180mm makes it very deep for a PSU of this power rating and
it could be a tight fit in cases that are not as deep as usual.

INSIDE THE SILENT PRO M2 720W

The casing is a clamshell design made of sturdy steel sheeting, with good fit
and finish.


The big rectangular cross section heatsink fins are very familar:
I know them to be the type used by Enhance
Electronics
, the most likely manufacturer of this PSU. The 135mm
fan has good geometry for low tonality — the blades’ trailing edges
are more or less perpendicular to the four struts.



The fan is made by Young Lin Tech, whose site tells us the specs: 12V,
0.2A, 2.4W, 1500RPM, 34.44dBA, 78.13CFM. It should not be a screamer,
based on those numbers.


The internal layout is roomy in comparison with recent higher efficiency
PSUs, and the heatsinks are big enough to seem retro. All the good PSUs
had similarly big heatsinks just a few years ago, but increased efficiency
has made them less necessary now.



The big caps are Matsushita/Panasonic —270uF, 420V, 105°C. Most
of the smaller caps are Teapo, also 105°C

OUTPUT CABLES

The detachable output cables are flat data-style and just long enough for cases
with bottom PSU placement, which puts the main ATX and AUX12V connectors on
the motherboard farther away.

Attached:
1 – Main ATX 20/24-pin connector, 55cm
1 – 4/8-pin + 8-pin AUX12V connectors, 60cm

Modular:
2 – 6+2-pin connector and 8-pin connector for video card, 72cm
2 – 3x SATA power connectors, 70cm
1 – 3x SATA power connectors, 94cm
1 – 3x 4-pin Molex power connectors, 70cm
1 – 2x 4-pin Molex and a floppy drive power connectors 95cm

The graphics card power cables are a bit troublesome: The combination of a
6+2-pin connector and 8-pin connector is impractical. Most graphics cards use
two 6-pin connectors, in which case both power cables must be used to power
just one PCIe card. It is possible to cut the plastic bit which makes it possible
to insert the 8-pin plug into a 6-pin socket, but why should the user have to
make such a modification?

TESTING

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

SPCR’s
PSU Test Platform V4.1
. is the basic setup for the testing. It is a close simulation of
a moderate airflow mid-tower PC optimized for low noise. There is one major change: The primary testing is done with the PSU NOT inside the hotbox but atop it, out of the heat path. This is in recognition of several realities that prevail today:

  • In SPCR’s earlier test platforms, the internal temperature varied proportionately
    with output load. The tested PSU was subject to this heat, and operating ambient
    temperature rose with increased load, reaching >40°C and often much
    higher at full power. This was a realistic simulation of a mid-tower PC case
    where the PSU is mounted conventionally at the top back portion of the case.
  • The vast majority of "serious" PC cases for the home builder place no longer position the PSU at the top back corner. They put the PSU at the bottom/back corner, mostly out of the path of heat from the other components in the case. This design concept took root with the Antec P180 going back over 5 years, and dominates the DIY case arena. This means the PSU generally has to dissipate only its own heat.

Now, we’ve reversed our approach: The PSU is tested briefly in
the hotbox only to check what happens to noise, fan speed and temperatures when
it is used in an outmoded case design.

Acoustic measurements are performed in our own anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

REAL SYSTEM POWER NEEDS: While we test the PSU to full
output 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 40W and 300W, because it is the power range
where most systems will be working most of the time. It is true that very elaborate
systems with the most power hungry dual video cards today might draw as much
as another 150~300W, but the total usually remains under 600W.

TEST RESULTS

The ambient temperature was ~22°, and the ambient noise level
was ~10 dBA.

Test Results: CoolerMaster Silent Pro M2 720W

DC Output (W)

AC Input
(W)
Heat loss
(W)

Efficiency %
Power Factor
Exhaust
SPL* (dBA@1m)
21.6
36
14.4
60.0
0.96
25°C
15
40.0
56
16.0
71.4
0.98
25°C
15
64.6
83
18.4
77.9
0.99
26°C
15
91.2
108
16.8
84.4
1.00
27°C
15
151.0
175
24.0
86.3
1.00
28°C
15
202.1
228
25.9
88.7
1.00
30°C
15
250.4
283
32.6
88.5
1.00
32°C
15
300.0
338
38.0
88.7
1.00
34°C
15
397.9
450
52.1
88.4
1.00
37°C
16
501.2
585
83.8
85.7
1.00
39°C
22
599.1
715
115.9
83.8
1.00
41°C
27
721.5
874
152.5
82.6
1.00
45°C
31
Crossload Test
(1A on 5V and 3.3V lines; the rest on 12V line)
459.0
515
56.0
89.1%
1.00
33°C
21
+12V Ripple (peak-to-peak): <10mV @ <200W
~ 32mV @ 720W
+5V Ripple (peak-to-peak): <8mV @ <200W ~ 20mV @ 600W
+3.3V Ripple (peak-to-peak): <8mV @ <200W ~ 20mV @ 600W
AC Power in Standby: 0.8W
AC Power with No Load, PSU power On: 13.3W / 0.33PF
* See text discussion about noise.

1. EFFICIENCY This is a measure of AC-to-DC
conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency means that to deliver 80W
DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU.
Higher efficiency is preferred for reduced energy consumption and cooler operation.
It allows reduced cooling airflow, which translates to lower noise. The 80 Plus
Bronze standard requires 82% efficiency at 20% load, 85% efficiency at 50% of
rated load, and 82% efficiency at full rated load.

At the super low 20W load, efficiency was low at 60% but rose
as the load was increased. 80% efficiency was reached around 70~75W. It easily
exceeded 82% efficiency at 20% of rated power, which in this case is 144W; at
150W, 86% efficiency was reached. A high of nearly 89% efficiency was reached
at 200W, and this high plateau was maintained to over 400W. This is way beyond
Bronze; it is higher than 80 PLUS Silver requirements and almost at the 90%
required for Gold. By 500W, the natural higher load efficiency sag was in evidence,
but better than required efficiency was maintained to full rated output.

There was no issue with crossloading. With over 90% of a 459W
load on 12V, naturally, efficiency improved over the standard loading.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintained within ±5%.

The critical 12V line was very well regulated. It started a touch
at very load load, +0.17V (1.4%). It dropped gradually as load was increased,
reaching a low of 11.94V (-0.5%), not at full power, but at 500W. The 5V line
was not quite as good, starting a touch high at 5.12V (+2.4%) and down to 4.8V
(-4%) at full load. 3.3V ranged from 3.34V to 3.22V (+1.2% to -2.5%). The VR
on the 12V line is excellent, and that on the lower voltage lines are well within
ATX specs, even if not quite stellar.

3. AC RIPPLE refers to unwanted "noise"
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was excellent
at all power levels, staying under 10mV at all power levels up to around 200W,
and only exceeding 30mV momentarily at full load only. This is excellent.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how "difficult" it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. Power
factor was very goodfor this model, running at or close to 1.0 (not never quite
reaching it) through most of the loads.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. Our sample had no issue starting up with no load, either, but the
power draw of 13.3W was a little higher than most recently tested PSUs. The
0.8W power draw in standby (power switch on but computer off) meets the <1W
requirement.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 500W load at va rious AC input voltages.
Most full-range input power supplies achieve 2~3% higher efficiency with 220~240
VAC, compared to 110~120 VAC. SPCR’s lab is equipped with a 240 VAC line, which
is used to check power supply efficiency for the benefit of those who live in
higher mains voltage regions. We also used a hefty variac to check the stability
of the PSU under brownout conditions where the AC line voltage drops from the
120V norm.

Various VAC Inputs:
CoolerMaster Silent Pro M2 720W
VAC
AC Power
DC Output
Efficiency
243V
432W
398W
92.1%
120V
450W
88.4%
100V
454W
87.7%

Efficiency improved to over 92% at 240VAC. The sample passed
the 100VAC minimum input at 400W (398W) load without any issues, with a 1.1%
drop in efficiency. Neither voltage regulation nor ripple changed appreciably
during these tests.

7. COOLING & NOISE

The 135mm fan in the Silent Pro M2 720W started up a low speed
with soft broadband audibility. It is a pleasant, low level whoosh devoid of
any annoying tonalities. On the spectrum analyzer, the overall SPL was ~15 dBA@1m,
which is one dBA higher than recorded for the Silent
Pro M 700W back in 2009
. Subjectively, this is about right — our beat-up
M 700W lab unit seems a touch quieter at residual/minimal load. No change in
the noise was detected till around 400W load, when perhaps a single dBA increase,
to 16 dBA@1m, was seen. At 500W load, the fan sped up more significantly, and
the SPL stabilized around 22 dBA@1m. From that point, the fan sped up progressively
with increased load, reaching a maximum of 31 dBA@1m at full load. Throughout,
the quality of the noise remained smooth and benign. No obvious electronic noise
was heard at any power load.

The exhaust air temperature rose somewhat higher, somehat more
quickly than usual beyond about 200W load. Another way of saying is is that
the temperature versus load curve is a bit steeper than usual — but keep
in mind that I’ve been testing 80 PLUS Gold and Platinum efficient PSUs almost
exclusively for the last couple years, and they run very cool, so my "normal"
here is a pretty tough standard. In any case, the Silent Pro M2 720W exhibited
no signs of heat related stress at any time during the testing, even at extreme
loads in the hotbox (see below) when exhaust temperature reached 60°C.

IN THE HOT BOX

When exposed to the heat of the hotbox, the Silent Pro M2 720W
fan started to spin up about 100W lower, but the overall noise profile did not
change. Even in an old-style case with poor fresh air intake for the PSU, the
Silent Pro M2 720W will remain quiet to over 400W load. This is very good performance.

CoolerMaster Silent Pro M2 720W SPL: In Hot Box vs. Out
Power load
<250W
300W
400W
500W
600W
720W
out
15
15
16
22
27
31
in hot box
15
16
21
25
31
32
Measurements are in dBA@1m
* See note in text above.

COMPARISONS

The comparison table below shows the SPL versus Power Load data on PSUs tested
in ambient room temperature, typically 20~24°C. It is most relevant when PSUs
are used in cases that provide wide open access to cooler outside air for the
PSU cooling fan. The Silent Pro M2 720W falls quite low on the list mostly because
so many o the other models here have a lower default noise level. But this is
somewhat misleading; as power load increases, the noise level of most of the
other models rises more, and to a higher level. At the 400W level, for example,
the 720W M2 is at the same level as the Seasonic X-650 (6 rungs up). It would
also be 3-4 rungs higher at the 500W level.

PSU Noise (dBA@1m) vs. Power in Ambient
Room Temperature
Model
90W
150W
200W
250W
300W
400W
500W
6-700W
850W

Kingwin Lazer Platinum LZP-550
<10*
<10
<10
<10
<10
<10
16
n/a
n/a

Seasonic X-400 Fanless
<10*
<10
<10
<10
<10
<10
n/a
n/a
n/a

Enermax Platimax 600W
<10
<10
<10
<10
<10
12
18
24
n/a

Enermax Modu/Pro87+ 500
11
11
11
11
11
11
18
n/a
n/a

Corsair AX850
<10
<10
<10
11~13
12
13
17
24
35

Seasonic X-650
<10
<10
<10
<10
<10
16
27
32
n/a

Nexus NX-5000
11
11
12
12
12.5
14
19
n/a
n/a
Antec CP-850
12
12
12
12
12
14
20
24
40

Enermax Eco80+ 500W
<11
12
12
16
20
23
28
n/a
n/a

Antec TP-750
12
12
12
14
15
27
31
40
n/a

Seasonic G360
<13
<13
18
24
34
39
n/a
n/a
n/a
CoolerMaster Silent Pro M2 720W
15
15
15
15
15
16
22
31
n/a
Cougar GX-700
15
15
15
17
21
25
35
35
n/a

The comparison table below shows the SPL versus Power Load data on all the
PSUs tested in the hotbox. It’s difficult to rank them, as the measured SPL
varies differently with power load. The units which are quietest at minimum
load are not always the quietest at midload (100W~300W), which may make them
louder in actual use. Then there’s the noise level at 400W and up, which will
determine the quietest PSUs for high power gaming rigs, during actual gaming.
In this environment, the Silent Pro M2 720W falls in the middle: It is very
quiet but not silent at low loads, and stays quieter than most to a higher power
level, and doesn’t get that loud even at very high power.

PSU Noise (dBA@1m) vs. Power in Hotbox/Anechoic
Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6-700W
850W

Seasonic X-400 Fanless
<10*
<10
<10
<10
<10
<10
n/a
n/a
n/a

Enermax Platimax 600W
<10
<10
<10
<10
12
16
21
24
n/a

Kingwin Lazer Platinum LZP-550
<10*
<10
<10
<10
<10
16
22
n/a
n/a

Enermax Modu/Pro87+ 500
11
11
11
11
14
20
23
n/a
n/a

Corsair AX850
<10
<10
12
15
18
25
35
38
39

Seasonic X-650
<10
<10
12
14
16
31
31
32
n/a

Nexus Value 430
11
11
16
18
18
19
n/a
n/a
n/a

Nexus NX-5000
11
11
12
14
22
24
25
n/a
n/a
Antec CP-850
12
12
12
14
14
26
40
44
45

Enermax Eco80+ 500W
<11
12
16
19
26
32
33
n/a
n/a
CoolerMaster Silent Pro M2 720W
15
15
15
15
16
21
25
32
n/a

Seasonic M12D 850W
14
14
14
14
14
24
37
42
42

Antec TP-750
12
12
14
14
18
33
40
40
n/a
Chill Innovation CP-700M
15
15
15
15
17
30
34
34
n/a
Antec Signature 650
15
15
15
18
18
28
36
47
n/a
Coolermaster M700W
14
14
18
21
25
27
34
34
n/a

Seasonic G360
<13
17
23
30
39
39
n/a
n/a
n/a
Cougar GX-700
15
15
18
20
25
32
35
36
n/a
SilverStone DA700
18
18
18
18
23
32
35
41
n/a
Nexus RX-8500
14
14
17
22
28
32
32
33
33
NesteQ ECS7001
22
22
22
21
23
25
36
37
n/a
PCPC Silencer 610
20
24
24
24
24
30
40
50
n/a

The green boxes are >30 dBA@1m SPL.
*<10= below the ambient of our anechoic chamber; immeasurably low
@1m in any environment

Caution: Please keep in mind that
the data in the above table is specific to the conditions of our test setup.
Change the cooling configuration, the ambient temperature and any number of
other factors, and you could change the point at which the fans start speeding
up, as well as the rate of the rise in speed. The baseline SPL is accurate,
however, probably to within 1 dBA.

CONCLUSIONS

The CoolerMaster Silent Pro M2 720W offers a nice array
of positive benefits. Energy efficiency at 200~400W is nearly in the Gold class,
a nice bonus given its Bronze rating, which can be attributed to its drop in
efficiency at the low and high end of the power curve. Its 12V voltage regulation
is superb, and the lower voltage lines are good enough. The noise and ripple
performance is excellent, on par with some of the best tested recently, and
it has no problem keeping itself cool. The build quality (with manufacturer
Enhance) looks solid, too. While not the quietest at <250W load levels, its
soft, smooth, broadband acoustic signature is very easy on the ears and increases
slowly with load.

Given the overall acoustic and efficiency curves, this CoolerMaster
might be just about perfect for an often-used gaming system with a somewhat
higher idle or low load power, game play loads of 200~500W, in a modern case
with good intake venting for the PSU. That power envelope covers a vast range
of systems with CPUs from either Intel or AMD, and graphics cards of mid-to-high
end from both nVidia and AMD that are not the latest generation — ie, cards
that don’t have as low an idle power as the latest. In such a system, the very-low-load
inefficiency of the Silent Pro M2 720W is not a detriment, its high mid-power
efficiency taken good advantage of, and its smooth low noise character will
always remain below the acoustics of the graphics cards.

About the only real quibble is the configuration of those power
cables for graphics cards with 6+2 pin and 8-pin connectors, which is poorly
thought out. This is not an insoluble problem as the 8-pin connector can hacked
for 6-pin operation if necessary. It could be that the latest shipping samples
have two 6+2 pin connectors for the graphics power cables, but if not, I’d call
CoolerMaster out on it. Finally, current retail pricing seems a bit on the high
side, especially as money has been saved by the exclusion of packaging fluff
like velour bags and cable pouches, but modular cables and a 5-year warranty
from a big brand like CoolerMaster might be worth paying for.

It’s easy to recommend the CoolerMaster Silent Pro M2 720W, especially
for the noise-shy gamer.

Much thanks to CoolerMaster
for the review sample.


CoolerMaster Silent Pro M2 720W is Recommended by SPCR

* * *

SPCR Articles of Related Interest:
Power Supply Fundamentals

Recommended Power Supplies
SPCR PSU Test Rig
Enermax Platimax 600W
Kingwin
Stryker STR-500

Seasonic G360
Enermax Modu87+ 500W 80 Plus Gold

Seasonic X-650: Seasonic Hits
Gold

CoolerMaster Silent
Pro M 700W

* * *

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this article in the SPCR Forums.

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