Stability Testing the PSU
You can check the 80 Plus measurements (taken with 115 V input voltage) here. During our tests, we monitor voltage fluctuations at different loads. We write down the lowest and highest values. You want as little fluctuations as possible. The ATX specification requires that the PSU stay within a 5% fluctuation; for example, each +12 Volt rail should remain between 11.4 and 12.6 Volts. This means that the PSU is operating within ATX-defined specifications. Below you can find thresholds in the table:
Now the measurements for the Seasonic FOCUS SGX-650 unit:
|
Voltage |
Threshold |
Minimum Voltage |
Nominal Voltage |
Maximum Voltage |
|
+3.3 V |
(±) 5% |
+3.14 V |
+3.3 V |
+3.47 V |
|
+5 V |
(±) 5% |
+4.75 V |
+5 V |
+5.25 V |
|
+12 V |
(±) 5% |
+11.4 V |
+12 V |
+12.6 V |
|
DC Output Load Regulation |
|||
|
Combined DC Load |
+3.3 V |
+5 V |
+12 V |
|
65 W (10%) |
3.34 |
5.04 |
12.11 |
|
162.5 W (25%) |
3.33 |
5.03 |
12.08 |
|
325 W (50%) |
3.31 |
5.03 |
12.04 |
|
487.5 W (75%) |
3.31 |
5.03 |
12.02 |
|
650 W (100%) |
3.30 |
5.02 |
11.99 |
All results remained safely within specification and tolerance thresholds. As you can see, when in use the PSU stays consistent. Voltages are very stable even at 100% load, and very close to the ideal values as per the ATX specification.
Sound levels (dBA)
As always, for sound levels measurement we’ve used the Voltcraft SL-100 dBA meter. The human auditory system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be if its energy was concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBA level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement. Frequencies below 1 kHz and above 6 kHz are attenuated, whereas frequencies between 1 kHz and 6 kHz are amplified by the A weighting. We measure the dBA 75 cm away from the product (the usual distance between you and a desktop computer). This is a rather subjective test. The lowest dBA level we can measure without any equipment activated is roughly 30 dBA in this room.
- At ~10% (idle) PSU is inaudible
- At ~ 25% you cannot hear the PSU
- At ~ 50% load you can barely hear the fan, it remains virtually silent.
- At ~ 75% load you can hear the fan, but it remains silent.
Below you can find the RPM behavior of the PSU fan:
The PSU remains silent under normal load conditions. The sound shouldn’t be noticeable in a system equipped with a CPU cooler, chassis fans, and a GPU (at least till let’s say 75-80% load).
If it’s under 38 dBA, you most probably won’t hear it at all, unless you bring your ears very close to the power supply unit. So the Seasonic PSU should be at least acceptable for most users even at 75% load.
