Silverstone Nightjar ST45NF: 450W Fanless Power Supply

TEST RESULTS

The ambient temperature was 21~22°, and the ambient noise level was 11 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 requires 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.

Our testing for <500W PSUs begins at a super low 20W. At this power level, the ST45NF 20W load, efficiency was decent at 61%. The 80% efficiency mark was reached at 80~90W, and crested 82% somewhere between 100W~150W. It was clearly over 82% at 150W, and climbed all the way to 87.8% at 200W, and stayed >87% to over 300W load. At 448W (full rated power), it was still at 83.3%.

This is excellent performance. In comparison to the 80 Plus test results, the findings on our sample show lower efficiency at low power and higher efficiency at the middle load. Surprisingly, despite the much hotter conditions of our test, efficiency at maximum power matched the 80 Plus results. See the cooling section below for more discussion about the measured temperatures and airflow patterns.

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 maintain within ±5%.

The critical 12V line was 0.29V (+2.4%) high at worst, and even at the highest loads, the voltages never dropped below 12V. The regulation on the less critical 3.3V and 5V lines was equally good. This is very good, far better than required.

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 very good at all power levels. At maximum power, the 12V ripple peaked at just 51mV, and the ripple on the other lines was about half that level.

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, running no lower than 0.92 at any point during testing.

5. LOW LOAD TESTING turned up an anomaly. On standby, the power draw was 2W, which is fairly normal. But with no load, while the PSU started, the power demand was a very high 45W, higher even than with a 20W load! The unit also emitted a buzzing that was not evident through real loads during testing. It would appear that a minimum loading circuit automatically kicks in when a no-load start is seen, perhaps to protect against damage. A no-load start is completely abnormal outside of lab testing; while this behavior might be interesting, it has no practical consequence.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load with 120VAC through the 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. The ST45NF is rated for operation 100-264VAC 50/60 Hz Most 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 to nearly 89% with 245VAC input at this load. The sample passed the 100VAC minimum input without any issues. (90VAC input also worked fine, but the data was accidentally not recorded.) Neither voltage regulation nor ripple changed appreciably during the test.

7. TEMPERATURE & COOLING

Please see the discussion on the previous page on interpreting the temperature data.

What the temperature data shows can be summarized as follows:

• For any given load level, the temperature in the test box was higher than with most fan-cooled PSUs. This is natural; there was only one fan, the 120mm case fan, blowing out the heat.
• The temperature of the back of the PSU got quite hot, especially at over 300W. Again, this is not surprising. However, there was no misbehavior of any kind during the load tests, and this includes any misbehavior that could be attributed to overheating.

As there were no other sensors, it's not known how hot the internal components got. But even if such data was collected, it would not be useful without some points of comparison; the internal temperatures of PSUs under test have never been monitored before. Suffice it to say that despite the high temperature in the test box, and on the external casing of the unit, the ST45NF performed well.

8. NOISE

This part of the review can be really short: There are no sound recordings, frequency spectrum captures or SPL measurements. Why not? Because there was no appreciable noise from the ST45NF at any point during load testing. Oh, if you get close enough in a quiet room, you can hear the trace of buzzing and whine common to all power electronic circuits. But in any normal application, you can call this power supply silent.

It's possible that a particular combination of loads with specific components might increase electronic noise to a point where it becomes audible, or that not all samples exhibit as low a level of buzzing as this one. However, having used several samples of the ST30NF in a number of different systems and witnessing no audible buzzing from any of them, it's probably safe to suggest that the silence of the test sample is not unusual.

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