Seasonic X-400 Fanless PSU

TEST RESULTS

The ambient temperature was 23~24°, and the ambient noise level was 14~15 dBA. The PSU was allowed to run at each power level for about 20 minutes before any measurements were taken.

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 90% efficiency at 50% of rated load, and 87% efficiency at both 20% load and full rated load.

Keep in mind that the testing for 80 Plus approval is done at normal ambient room temperature. The 80 Plus Testing Guidelines (PDF) specify only that "ambient temperature shall be maintained at 23°C ± 5°C throughout the test." In contrast, the ambient temperature of the SPCR test system is directly proportionate to the load. At low load, the air intake is at or just above room temperature, but as load is increased, the temperature rises steadily. This is an extremely tough test condition, as PSU efficiency naturally drops off at high and low loads; combine high load with high temperature and it's essentially a PSU torture chamber.

At the super low 20W load, efficiency was excellent at 69.8%, compared to 65% in the X-650. Efficiency rose quickly as the load was increased. 80% efficiency was reached around the 40W mark, but our sample did not quite reach 87% at 80W (as called for in the 80 Plus Gold requirement). It probably consumed 1-2W more than required, as 86% efficiency was seen at 90W load. (A Chroma PSU test report Seasonic ran on this very sample and sent along as part of the reviewer package showed 87.84% efficiency at 80W load. We're inclined to trust their Chroma report more than our own test result; there are undoubtedly a few points of departure from "true" values on our homebrew rig.) By 150W, efficiency reached nearly 90%. At 200W, >92% efficiency was reached. With higher load, and higher operational temperature in the SPCR test box, efficiency dropped a bit, but still remained just about at 90% even at full power, at over 40°C temperature in the hotbox.

These are great results, as expected. We've never seen such high efficiency at such low loads, and the efficiency curve is extremely flat, despite the absence of active cooling for the PSU. The 90% efficiency at full load was a real surprise, as we expected it to sag much lower in the hot conditions.

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 0.2V (~1.7%) of 12V, and even at the highest loads, it never dropped below 12V. This is excellent performance. The 3.3V regulation was within 0.08V, while the 5V line was off by 0.06V (2%) at worst. The sample exceeded Seasonic's own stringent 3% spec for voltage regulation.

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 absurdly low at all power levels. Even at maximum power, the 12V ripple stayed under 20mV. Along with the Seasonic X-650, it is the best ripple we've 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 near perfect throughout the test range.

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 much lower than normal.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load with 120VAC through a hefty variac in the lab. The variac was then dialed 10V lower every 5 minutes. This is to check the stability of the PSU under brownout conditions where the AC line voltage drops from the 110~120V norm. 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 240VAC mains regions.

Efficiency improved around 2.4% with 244VAC input at this load. The sample passed the 100VAC minimum input without any issues. Neither voltage regulation nor ripple changed appreciably during the test.

7. TEMPERATURE & COOLING

As mentioned earlier, the flipped over recommended position of the X-400 Fanless gave it a distinct advantage in our PSU test hotbox. Nevertheless, it's impressive how cool the unit really ran. Note that the "exhaust" temperature isn't really that; the thermal sensor was simply stuck on the middle of the back panel. Periodic spot checks with an infrared non-contact thermometer showed temperatures of 65~70°C around the heatsinks and the main capacitor during the 20~30 minutes of operation at full 400W load, which caused no distress whatsoever.

8. ACOUSTICS

Normally. this is the end of our electrical and thermal performance analysis, and we move on to acoustics. However, there's simply no acoustics to be discussed. There are also no recordings of the PSU's noise. The X-400 Fanless remained silent from no load all the way to full 400 load throughout the testing period. This is not to say the silence was absolutely complete; from 6" away, at some load combinations a faint buzz could be heard. But for all practical purposes, the X-400 is indeed silent. We said this about the Silverstone ST45NF; this Seasonic is at least as quiet.

9. LONG TERM, FULL POWER, THERMAL TORTURE TEST

This is a test we have never run on any PSU before: Long-term, full load test without an exhaust fan in our PSU hotbox. It was mentioned earlier that even running this box without the exhaust fan is not normal. Commercially manufactured PSU load testers have non-defeatable, multiple high speed fans to keep themselves cool. This is a major reason why we use our custom-cobbled load tester: It lets us turn the fans off entirely when measuring or recording PSU noise. So why run this test on the X-400 Fanless? Well, almost on a dare.

In direct discussions about the X-400 Fanless, Seasonic reps were brimming with confidence that their new baby could not only perform just like a fan-cooled 400-watter, but even deliver full power under extremely low airflow conditions, such as one might find in a fanless (or single fan) silent PC. The parts in the X-400 FL are apparently robust enough that if it was fan cooled, it could easily be rated for 700W. This led to our running the normal tests without an exhaust fan. When our Seasonic rep found out the 30 minute duration of the 400W test load, he wanted us to try running it at full power for 24 hours, as is often done for testing of mission-critical server PSUs — which are never fanless.

The challenge was on. So, the X-400 Fanless was set to full load without any exhaust fan in the test hotbox, and left to run as long as possible. It was decided early on that 24 hours continuous was not going to be practical. For safety reasons, the test would be monitored regularly (about once every half hour) by a physically present person. That's your author. The test was begun at about 8 AM with 22~23°C ambient room temperature, and left to run until 11 PM that night, a total of 15 hours. The ambient temperature in the room climbed to 26~27°C by 1 PM, stayed around there for several hours, and only declined down to 24°C at 11 PM.

The temperature in the hotbox directly beneath the PSU ranged 56~60°C. Spot checks with the aforementioned infrared thermometer showed temperatures inside the X-400 as high as 82~84°C; mostly it hovered close to but under 80°C. The efficiency dropped as the PSU heated up. The 444W AC input seen after half an hour rose gradually about 10~12W higher during the hottest part of the day.

The end result after 15 hours: The X-400 Fanless survived the test. Furthermore, it worked perfectly the next day — and ran another 12 hours at the same load and conditions. At the end of the second day, a 1500W hair dryer was brought into play while the PSU was at full load, blowing the hot air down into the open grill cover of the X-400 to see what would happen with thermal overload. In a minute, the PSU shut down with a little click, the Over Temperature Protection finally kicking in. The IR thermometer showed temperatures of over 90°C around the main heatsinks. The AC cord was unplugged, the power switched off for a few minutes, then it was turned back on — with no change to the load settings: The X-400 powered back up without a hitch and kept running. The hair dryer was used several times to force OTP, just to check on the protection function. It worked without a flaw about half a dozen times. The X-400 sample is now powering a new system being set up for use in the lab.

It's hard to imagine any other fanless PSU surviving our long term full power torture test... but it was a valid question that came up, a question that we decided to answer in Fanless PSU Torture Test Roundup.

10. IN A REAL SYSTEM?

How would the X-400 handle the heat in a real computer case where the top would not be so wide open to the outside air? The answer is that it will probably do fine in most systems (and modern cases) that are reasonably thought out for cooling, even with minimal airflow. Consider the following points:

• The way most people and programs use real computer systems results in dynamic — constantly changing, that is — power demand. Most computers run pretty close to idle much of the time, with short peaks into high power. Even modern 3D gaming doesn't redline the PC constantly, there is always some up/down in power. In other words, our torture test of the X-400 Fanless is an unrealistically extreme, worst case scenario.
• One of the advantages in a real computer is cooling by conduction from the casing of the PSU to the metal case to which it is tightly bolted. This conduction cooling is missing in our test hotbox.
• Since HTPC system are probably the first target market, consider that many of the best HTPC cases we've reviewed have excellent airflow and open venting in, around or near the PSU. Think of Antec Fusion, Fusion Max, Silverstone GD05/06, for example — all place the PSU with space over it and vent holes or grills to the outside.
• Then there are the many mid-tower and larger cases that put the PSU at the bottom, either with venting above or below, where you can experiment with flipping the X-400 one way or the other. The X-400 would fare well in such cases. Think Antec P180 series, Antec 3480 (with open vent above PSU), Antec gaming cases, Fractal R2, Silverstone Raven and Fortress models, Coolermaster's CM690, CM Storm, HAF series, and a dozen Lian Li models with bottom PSU placements. In fact, the bottom mounted PSU is almost the rule among quality performance cases these days.

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