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Seasonic SS-350TGM 80 Plus Gold TFX

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Seasonic introduces 80 Plus Gold efficiency PSUs in TFX12V form factor with semi-passive, hybrid cooling for mini-towers and compact media PCs. Will system integrators embrace these new 300W and 350W PSUs?

Product
SS-350TGM
TFX power supply
Sample Supplier
Seasonic USA
Manufacturer
Seasonic Electronics
Price
US$70??

It is ironic that while the average power demand of desktop CPUs has dropped
dramatically so that they now rarely draw more than 10W at idle, the average
computer power supply rating has gone in the opposite direction. Kilowatt and
higher rated power supplies abound more than ever, and there are only a handful
of name-brand retail ATX PSUs rated at below 450W. On the other hand <150W
DC/DC converter boards with external AC/DC power adpters have become the norm
for SFF computers. But if you want a quality power supply built into a modern,
compact PC, the 200~400W area is barren.

The SS-350TGM and 300TGM TFX power supplies from Seasonic fit into this niche.
Their combination of modest power and 80 Plus Gold ratings is rare in the retail
market, where most 80 Plus Gold PSUs are at least 400W, and more commonly 600W
or higher. It is not so unusual among PSUs made specifically for big OEMs, who
rarely pay for unnecessarily high powered PSUs. The TFX form factor means that
the TGM series PSUs cannot be dropped in as a replacement for any ATX power
supply, however; it is housed in a smaller, but longer-shaped housing.

TFX power supplies are also uncommon in retail cases, although the Antec
NSK1480
HTPC case we reviewed a couple years ago comes to mind. They
are much more widely used by big system integrators in SFF or low profile systems.
Current PCs that utilize TFX power supplies include the HP Pavilion Slimline
series (model
s5xt
, for example) and most Dell Slim Tower models (such as the
Inspiron
620 ST
). Going back to retail component markets, the class of cases
Newegg refers to as MicroATX Slim are similar in size and shape
to the aforementioned slim PCs. The selection of such cases is not large, and
they tend to be basic, low-cost products that usually come with a PSU.

Our Seasonic SS-350TGM TFX PSU sample came without any retail packaging, as befits a product that will be used mostly by system integrators.

VISUAL TOUR

The SS-350TGM is painted classic battleship grey. As with the vast majority of PSUs in the TSX form factor, the cooling fan is 80mm in diameter.


The SS-350TGM sports the typical OEM color: Grey. An 80mm cooling
fan at a right angle to the small vent at one end of the casing, as
per the TSX norm. The intake vent over the fan is about average, probably
blocking ~20% of the potential airflow. There is no power switch.


Here is a major departure from the norm: Totally detachable output cables.
In the past, Seasonic was reluctant to use them on lower power PSUs, citing
losses in the contacts as hurdles to high efficiency. My guess is that
the technology developed in the X series has helped Seasonic overcome
this challenge.


All the output cables are on a single assembly, without sleeving.


The cables are appropriately short, because TSX PSUs are usually used
in small cases. Provided are connectors for four SATA drives, two old
4-pin Molex, a floppy drive, the main 24-pin ATX and a 4-pin AUX12V. (Note:
The 4-pin AUX12V will work even in an 8-pin AUX12V motherboard socket.)



The low voltage lines get 80W total (plenty for a modern PC) while almost the entire rated power is available on 12V (as it should be), split on two rails. My guess is that the AUX12V is on one rail while the rest of the outputs share the other 12V rail.

FEATURES & SPECIFICATIONS

Unlike retail package models, the marketingspeak (see Orwell’s "newspeak"in
1984) for the SS-350TGM is limited to a single web page, and fairly low key.

SEASONIC SS-350TGM FEATURE HIGHLIGHTS
(from the
product web page
)
FEATURE & BRIEF Our comment
Compliance with TFX12V v2.31 Differences between this latest and
earlier TFX12V specs are not clear because the spec doc is currently unavailable
at Form Factors.
• Support the latest Intel & AMD
Socket
• High efficiency and reliability
• Low ripple & noise
OK. Note that warranty is unspecified.
DC to DC converter design Used also on X series.
Super low noise fan control Like other current Seasonics?
• 100% hi-pot test
• 100% burn in, high temperature cycled on/off
This is expected
Certifications: CUL, TUV, CB,
CE, FCC, C-tick
As expected.
• Short circuit protection
on all outputs
• Over voltage protection
• Over power protection
OK.
Full Range Input 100 ~240V (Active
PFC)
Like most good PSUs
Physical: 175mm (6.9")
x 85mm (3.3") x 63.5mm (2.5")
Standard TFX12V size.
Note: Formfactors.org
no longer lists the recommended design guidelines for various desktop PSU
variants in separate documents. The TFX12V v2.3 specifications are contained
in the Power Supply Design Guide for Desktop Platform Form Factors,
Rev. 1.1 dated March 2007. This PDF file is downloadable from Form Factors.
SEASONIC SS-350TGM SPECIFICATIONS
AC Input
100~240VAC, 10A, 50/60Hz
DC Output
3.3V
5V
12V
-12V
5Vsb
12A
16A
29A
0.3A
2A
80W
348W
3.6W
10W
350W

There is no mention anywhere of temperature limits for power
output. We can assume the PSU is not designed for long term survival at >50°C
working ambient.

I took a quick peek inside the unit by undoing four screws. The internal tidiness should not have surprised me, with all the Seasonics I’ve opened up in the past, but given the small size of the unit, it was still nice to see.


Very tidy inside, with no point-to-point wiring. There are three
daughter boards mounted on the main PCB. The main capacitor is a high
quality 105°C 420V 220µF.


This angle clearly shows the DC/DC board to which the output connectors
are directly mounted, very similar to the board and scheme used in the
X series PSUs.


The 80mm fan is a 15mm thin ADDA AD0812MB-D90, rated for 3500rpm and 40dBA.
Not exactly quiet at full speed, as is the case for most PSU fans.

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 test platform, 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.

With the current test, we’re reversing our approach: The PSU will be tested briefly in the hotbox only to check on 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 11dBA or lower, with a PC-based
spectrum analyzer
comprised of SpectraPLUS software with an 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 30W and 300W, because it is the power range
where most systems will be working most of the time. With virtually no power
demand at idle from some CPUs and GPUs, some PCs can idle at <20W.

It is true that a very elaborate system with two of the most power hungry video cards today might draw as much as another 150~400W at maximum, but the total should remain under 700W in most cases.

TEST RESULTS

The ambient temperature was 22-23°C, and the ambient noise
level was ~10.5dBA.

Test Results: SEASONIC SS-350TGM

DC Out (W)

AC Input
(W)
Heat Loss
(W)

Efficiency %
Power Factor
Exhaust
SPL* (dBA@1m)
21.7
28
6.3
77.4
0.89
22°C
N/A
39.4
47
7.6
83.8
0.94
22°C
N/A
65.1
74
7.5
87.9
0.96
26°C
N/A
89.0
100
11.0
89.0
0.97
29°C
N/A
150.9
164
13.1
92.0
0.99
34°C
12
199.9
217
17.1
92.1
0.99
39°C
12
248.6
269
20.4
92.4
0.99
39°C
17
299.9
329
29.1
91.2
1.00
44°C
29
349.9
385
35.1
90.9
1.00
44°C
38
Crossload Test
(1A on 5V and 3.3V lines; the rest on 12V line)
350
382
32.0
91.9%
1.00
44°C
38
+12V Ripple (peak-to-peak): <17mV @ <150W
~ 45mV @ 350W
+5V Ripple (peak-to-peak): 5mV @ <150W ~ 14mV @ 350W

+3.3V Ripple (peak-to-peak): 5mV @ <150W ~ 15mV @ 350W
AC Power in Standby: 0.4W
AC Power with No Load, PSU power On: 7W / 0.68PF
* 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 Gold standard requires 87% efficiency at 20% load, 90% efficiency at 50% of rated load, and 87% at full rated load.

At the super low 20W load, efficiency was excellent at over 77%.
Efficiency rose quickly as the load was increased. 87% efficiency was reached
around the 65W mark (lower than the required 70W load), broke 92% by 150W, and
stayed above 90% all the way to 350W load. This is better than required by 80
Plus Gold, approaching Platinum at higher power loads.

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%.

At all load levels, the critical 12V line was within +0.22V (1.8%)
and -0.18V (1.5%) of 12V. It started high, at 12.22V, and dropped with increased
load to 11.82V (-1.5%) at full load. The 5V line was dead on almost all the
way to maximum power, where it dropped marginally to 4.98V. The 3.3V ranged
from 3.38V to 3.35V. These are excellent results, better than voltage regulation
needs to be for any PC.

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, generally staying under 15mV through the lower half of
the power range. Even at maximum power, the 12V ripple stayed at just 45mV.
This is very good, though not excellent, performance.

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 good for this model, running at or close to 1.0 through most
of the loads and no lower than 0.89 even at just 20W load.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. Our sample had no issue starting up with no load, either, and the
power draw was low. The 0.4W power draw in standby (power
switch on but computer off) is excellent.

6. LOW & 240VAC PERFORMANCE

The power supply was set to 200W load at various AC input
voltages. Most full-range input power supplies achieve higher efficiency with
higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, which was
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: SEASONIC SS-350TGM
VAC
AC Power
DC Output
Efficiency
244V
212W
200W
94.3%
120V
217W
200W
92.1%
100V
222W
200W
90.1%

Efficiency improved to over 94% at the higher voltage. This is
higher than the minimum 92% required by the 80 Plus Gold standard for 230VAC
operation. The sample passed the 100VAC minimum input at 200W load without any
issues. Neither voltage regulation nor ripple changed appreciably during these
tests.

7. TEMPERATURE, COOLING & NOISE

Despite the absence of the marketing hoopla that usually accompanies
sophisticated fan control systems, the SS-350TGM is equipped with the same semi-passive
cooling scheme as the X series PSUs. The fan does not start up at turn-on. The
only noise it emits is a very low level of electronic buzz, soft enough that
it is difficult to hear from over a foot away and immeasurable in my anechoic
chamber at 1m distance. This electronic buzz does not appear to rise as load
is increased.

In our test setup with a modest 22-23°C ambient, the fan did
not turn on until 150W load was applied. The fan was barely audible, at 12 dBA@1m,
just above the ambient in the anechoic chamber, even though it had the distinct
ball-bearing sound — a bit of chattering or clicking — from up close.
At 250W load, the fan became more clearly audible, measuring 17dBA, but still
not intrusive. Above that load, there was a rapid jump in fan speed and noise,
to 39 dBA at 300W and 44 dBA at full power. The high load fan behavior is typical
of Seasonic PSUs, which have usually favored good cooling over low noise at
high load.

With the long and narrow shape of the PSU, the temperature of
the exhaust air may be less indicative of real internal temperatures. In any
case, all of our exhaust temperature readings are little more than a gauge of
internal heat; the more precise measure of heat is the number of watts lost
as heat. Still, the SS-350TGM never seemed to get very hot, with maximum exhaust
temperature reading just 44°C. The high efficiency ensures that only a minimal
amount of heat be dissipated, and the maximum amount (at full power) is just
35W.

IN THE HOT BOX

Exposed to the heat of the hotbox, the SS-350TGM fan sped up at
a lower power load, but its overall power/noise ratio retained the same basic
shape. Keep the load under 250W, even in a system that’s not well ventilated,
and this PSU will stay very quiet.

SEASONIC SS-350TGM SPL: In Hot Box vs. Out
Power load
90W
150W
200W
250W
300W
350W
out
N/A
12
12
17
39
44
in hot box
N/A
12
17
22
41
44
Measurements are in dBA@1m

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 modern cases that provide wide open access to cooler outside air
for the PSU cooling fan. Although its noise level is competitive with all the
PSUs on the table at <250W loads, the 80mm fan’s rapid increase in speed
as its maximum load is approached puts it at the bottom of the list. The thing
to remember is that its maximum load is just 350W, and it is highly unlikely
to be used in a system that draws more than 250W peak.

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 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
Cougar GX-700
15
15
15
17
21
25
35
35
n/a
Seasonic SS-350TGM
<10*
12
12
17
39
44
n/a
n/a
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 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.

The SS-350TGM’s acoustics in the hotbox are competitive with some of the quietest
PSUs at <200W load, but above that level, it is middling at best. Again,
keep in mind its intended application, in PCs with maximum draws of <250W.

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

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

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
Seasonic SS-350TGM
<10*
12
12
17
39
44
n/a
n/a
n/a
Coolermaster M700W
14
14
18
21
25
27
34
34
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 Seasonic SS-350TGM power supply is another useful addition
to Seasonic’s large range of near-silent, >90% efficiency power supplies.
Its hybrid, semi-passive cooling with no fan movement at low load is a feature
that has been seen only in sophisticated higher priced ATX PSUs, and this feature
makes it a natural pick over any other TFX PSUs I’ve encountered or read about.
The high efficiency is what makes the semi-passive fan possible in the small
constricted TFX form factor. There is so little heat to dissipate.

The electrical performance of the unit is excellent in most ways.
About the only quibble might be the slightly higher 45mV ripple on the 12V line
at full power, but this is still 25% below the maximum 60mV recommended value.

While DIY PC enthusiasts may not have much to celebrate here due
to the dearth of cases that utilize TFX PSUs, system integrators obviously have
a new and better option for a quieter PSU in small tower or media PC systems.
The $70 price is a guess at what these units might sell for if it was made available
for retail purchase (as OEM PSUs often are). The 300TGM, a 300W version of this
PSU, might be even better suited for the latest generation of super energy efficient
PCs. We can certainly hope manufacturers create more low profile, compact media
PC cases to take advantage of these new TFX PSUs from Seasonic.

Much thanks to Seasonic
USA
for the review
sample.



Seasonic SS-350TGM receives the SPCR Recommended Award.

* * *

SPCR Articles of Related Interest:
Seasonic X-1050 PSU: Gold at Kilowatt+
Fanless PSUs: Kingwin Stryker STR-500 & Silverstone ST50NF

Fanless PSU Torture Test Shootout
Kingwin LZP-550 80 Plus Platinum
Recommended Power Supplies
Power
Supply Fundamentals

SPCR PSU Test Rig V.4

* * *

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