Seasonic X-1050 PSU: Gold at Kilowatt+

Seasonic recently entered the ranks of kilowatt PSU makers with new 1050W and 1250W models in its X series, and a 1000W model in its new X-derivative Platinum line. Our acoustics-focused review of the 80 Plus Gold approved X-1050 finds Seasonic in fine form.

Seasonic has moved steadily from success to success since entering the retail computer supply market about a decade ago. The 30+ year old power supply maker’s greatest success may be its recent X series, the first of which we reviewed in fall 2009. The X series burst on the scene with umpteen advanced features, impeccable performance, and superb build quality, and became the high bar for others to try and leap.

When first introduced, the highest rated model in the X series was 850W; recently, Seasonic finally entered the ranks of kilowatt PSU makers with new 1050W and 1250W models in its X series, and a 1000W model in its new X-derivative Platinum line (about which OklahomaWolf asks in his amusing and highly informative review, “How the hell is anybody going to top this one?”).

Seasonic management had been reluctant to introduce super-power PSUs for many reasons, including the desire to ensure 100% reliability even when pressed to deliver full power for extended periods, something they felt was not likely with many kilowatt+ models from their competitors.

It is the super-high efficiency of their new 80 Plus Gold and Platinum series which persuaded Seasonic decision makers to go for the kilowatt models. With such high efficiency, the maximum heat that must be dissipated at even 1000 W output is only around 100W, compared to double that with PSUs which meet the original 80 Plus requirements.

PACKAGING

FEATURES & SPECS

VISUAL TOUR

As with the other models in the X series, the casing is a departure from the normal dual C-shaped clamshell for PSUs. It is a 5-sided box with a cover, the fan panel. The metal feels thicker than usual and is fitted together very precisely — though Seasonics have always had excellent mechanical integrity. The black and gold color scheme continues.

A change from the lower power models is the gold colored inset grill, which makes the removable panel a 2-piece affair. This appears a purely cosmetic feature designed to differentiate the X-1050 and and X-1250 from the lower power models.

GOING INSIDE

As expected, many of the key components are similar to those found in other X series models. Specifically, the excellent Sanyo Denki 12 cm fan, the unique DC/DC Connector Module daughterboard that holds all the output connectors, and all the high quality parts listed in Seasonic’s PR material. Many of these items are closely detailed in our review of the X-650.

Opening up the unit required six screws to be removed. Layout is very tidy, as usual for Seasonic, especially since all the lower voltage conversion circuitry is relegated to the back output daughter PCB closest to the output connectors. Note the stiff plastic sheet baffle, meant to ensure no short-circuit of airflow from fan to exhaust vent. It is smaller than others we’ve seen Seasonic employ before, presumably because the fan is located farther back from the exhaust in this longer casing. This will mean less turbulence noise, at least not until the fan is spinning really fast, at which point, any hope of low noise can be tossed. As with the lower power X models, the heatsinks are shockingly small for someone used to seeing massive ones in earlier, lower efficiency PSUs. This is a >1000W power supply, after all! Greater detail for those who appreciate them… …and from the other side as well.

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:

• 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.
• In earlier versions of 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.

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 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, most desktop PCs
do not require anywhere near this level of power. The most pertinent range of
DC output power is between about 40W and 400W, because it is the power range
where most systems will be working most of the time. It is true that very elaborate gaming systems with two of today’s most power hungry
video cards might draw as much as another 300W.

TEST RESULTS

The ambient temperature was 21~23° (it rises over the duration of the test, due to the PSU testing itself), and the ambient noise
level was ~10.5 dBA.

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. 80 Plus Gold calls for 90% efficiency at 50% of rated load, and 87% at 20% and 100% load.

At the super low 20W load, efficiency was decent but not great at 72%. Efficiency
rose relatively slowly as the load was increased. 90% efficiency was reached around the
200W mark, and peaked a bit over 91% at 400~500W. It measured 87% at 1050W. The X-1050 passes 80 Plus Gold requirements easily at the 20% load, and meets them at 50% and 100% 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%. Seasonic claims 3% tolerance on all lines.

At all load levels, the critical 12V line was within -0.26V (-2.2%)
of 12V. It started a titch high at 12.1V and dropped with increased load to 11.74V (-2.2%) at full power. The 5V line also started a touch high at 5.1V (+2%), and went down to 4.86V at full load (-2.6%). The 3.3V line was rock steady at 3.35~3.30V throughout the testing. These are excellent results, staying well within Seasonic’s stringent ±3%, and 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 100 KHz or even higher). 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 very good
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 34mV.
It’s close to the best we have measured.

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 excellent for this model, running at or close to 1.0 through most
of the loads and 0.9 even at just 20W load.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. The 0.3W power draw in standby (power
switch on but load tester off with nothing loading the 5V standby line, like a USB device would do) is about the l owest we’ve measured. The
draw of 16.7W with power on at no load is substantially higher than we’ve seen in most recent PSUs. This is not exactly anything to worry about, as the condition is not one you’ll ever run into in real usage. We run the test as a matter of curiosity… and tradition: we’ve been reporting this for a long, long time.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 700W 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.

Efficiency improved to over 92% at the higher voltage, which is the efficiency required for the 80 Plus Gold in 230VAC operation. The sample passed the 100VAC minimum input at 700W load without any issues.
Neither voltage regulation nor ripple changed appreciably during these tests.

7. TEMPERATURE, COOLING & NOISE

Our X-1050 sample exhibited no audible high pitched noise, hum or buzz at any time during testing. It may have been there during high power loads, but the fan would have masked it. At <700W, no trace of this kind of noise was heard, at least not from >6″ away. I pressed my ear up to the unit at 200W in hybrid mode with every fan in the anechoic chamber turned off and maybe heard a trace of… something. This is the lowest electronic noise I’ve encountered in any PSU I tested or used in the last 10 years. Outstanding. We can all hope that this is typical of X-1050s… and perhaps all new production runs of X series models? (There have been some user reports of electronic noise in X series PSUs.)

Seasonic explains the switchable cooling modes on the X-1050 with the following graphic. Basically, in Normal mode, the fan starts at a very low speed and does not run faster until about 50% load (525W) is reached. In Hybrid mode, the fan does not start till about 30% load, but behaves the same as in normal model after it starts spinning. Since the fan speed is controlled by a thermal sensor rather than a load sensor, these trigger load numbers are based on Seasonic’s estimates of temperatures in typical use situations; i.e., the trigger points may occur at higher or lower power, depending on thermal conditions, which include not only the computer but the ambient room temperature.

In Normal mode, the fan started immediately at the very quiet level of 16 dBA @1m when our sample was powered on. The fan on our sample was just as smooth and unobtrusive at this speed as the other Sanyo Denki fans Seasonic has used in its X and M series for the last couple of years. True to Seasonic’s explanation, the fan speed did not change until well above 500W. Given that the ambient test room temperature was just 22°C, you can expect the fan to speed up at a lower load in summer, hotter climates, or in a computer where the PSU fan draws air from inside the case.

In Hybrid mode, the fan actually began spinning at around 200W, much lower than the 30% load indicated by Seasonic. But before you claim foul, it should be explained that the fan spun up for only perhaps 10 seconds, and never reached the same velocity or noise level as in Normal idle mode. It spun up, then turned off almost immediately, so the impact on overall noise was virtually nil at first. This was the behavior — a short period of spin-up followed by a longer period of no motion — between 200W to around 500W. The periods of no fan motion got shorter and shorter as the load was increased so that by 500W, the fan was running steadily at the same speed as in Normal idle mode. As our measurement tables indicate, the noise rose gradually in level. You might wonder reasonably whether the fan on-off cycling was audible or annoying. My assessment is that because the fan spun for such a short time, the noise level was too low to be easily noticed. By the time the noise rises to an audible level (say >400W), other components in your PC, such as the CPU and video card fans, will make considerably more noise than the X-1050.

Another phenomenon to note is that the reported exhaust temperature is the highest seen at each power level in Hybrid mode, but the fan cycling behavior in this mode should have tipped you off to the fact that it actually varied quite a lot. When the fan was not running, our thermal sensor at the exhaust vent of the PSU displayed ~35°C, even at 400W load. It was when the fan did its brief spin-up that the temperature rose to the above cited levels. So what is happening is that at 200~500W load, some components in the PSU get hot enough to trigger the fan turn-on, which forces the heat out of the PSU, and resulted in the 46°C peaks at 250W and 300W. But those components cool off fast so that just a few seconds of the cooler ambient airflow is enough to trigger the fan turnoff. Note how the peak temperature dropped to 42°C at 400W; this was when the fan was spinning for longer periods.

The fan sped up enough between 500W and 700W that the measured SPL rose by 10 dBA, making it plainly audible, though not particularly annoying. The fan’s basic acoustic signature is quite smooth. It’s unreasonable at this point in technological development to expect silence from an ATX power supply outputting 700W. Maximum noise and fan speed was reached at around 800W. No matter how you slice it, 40 dBA is noisy by our definition, but there isn’t a PSU out there which is quieter at >1000W load. What’s important at this power level is to keep the components from overheating. If you have a system that can draw a kilowatt, every other fan in the PC will be screaming louder anyway.

IN THE HOT BOX

In the hotbox, the X-1050 fan behaved almost the same as outside the hotbox. The basic difference was that the fan starting spinning steadily at a touch lower power level, and also got slightly louder at 700W load. Higher efficiency models invariably fare better in the hotbox, because they create less heat.

COMPARISONS

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 Seasonic X-1050 acoustics in the hotbox is up near the top of the pack, aside from the best fanless models. At every load up to its maximum, the unit is quieter than all other tested fan-equipped PSUs. At 6~700W, it is by far the quietest.

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

Seasonic’s drive to improve acoustics and efficiency in its power supplies has been a constant for the past decade. The X-1050 extends into the kilowatt circle all the benefits of the X series we documented in our X-650 review. This power supply boasts extremely high voltage regulation, very low ripple and noise, extremely low acoustic noise under varied conditions, very high energy efficiency, super quality parts and a robust build quality.

A notable quality (at least in our sample) is the absence of any audible electronic hum, buzz or whine. This is exceptional, the best I’ve ever encountered in a decade of testing power supplies.

For those who need or want a power supply that delivers over a kilowatt, Seasonic X-1050 is an excellent choice. It is far better than actually needed for any computer. Even the $219 pricing seems perfectly fair. The X-1050 deserves our highest recommendation.

Much thanks to Seasonic USA for this review sample.

SPCR Editor’s Choice Award

SPCR Articles of Related Interest:
Power
Supply Fundamentals
Corsair Gold: AX850 Power Supply

X-650: Seasonic hits Gold
Fanless PSUs: Kingwin Stryker STR-500 & Silverstone ST50NF

Fanless PSU Torture Test Shootout
Kingwin LZP-550 80 Plus Platinum
Recommended Power Supplies
SPCR PSU Test Rig V.4

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