Start-up and shut-down voltage
This chapter should be read with caution and attention as long as the fans are not purely analog, i.e. DC-controlled fans with 3-pin connection. The PWM control electronics almost always stand in the way of clean voltage regulation and it is therefore also not advisable to regulate PWM fans via voltage. Nevertheless, we have also carried out this measurement for all models, regardless of whether they are DC or PWM fans, because even strange results say a lot about the control electronics and the use as a DC-controlled fan.
But first we check the maximum speed at 100% PWM and compare it with the datasheet. The fan manages the specified data, the 9 rpm are within the tolerance range, especially since fans often “run free” a bit in the course of more than 50 operating hours.
In today’s test, we see that Blacknoise’s fan can handle low voltages starting at 3.3 volts, while Noctua’s fan needs at least 4.4 volts. In addition, all fans only reach the maximum speed and sufficient throughput as well as static pressure when PWM-controlled, so neither of them are pure DC solutions.
Neither of these provide the best electronics in terms of DC control, as the cut-off speed is well above start-up speed and not within the range of good DC-controlled fans. Here, the electronics simply run amok at some point when regulating the voltage downwards and the fan suddenly stops, although much lower speeds were possible when starting up. One of the special features of PWM fans is that there are no standards below 20%. Some fans just won’t slow down no matter what you set them to, or they’ll rev up to full speed again at zero percent.
Blacknoise advertises semi-passive operation here, which means nothing else, that the fan stops when the PWM setting is too low, and then also starts up again safely when you get over the point. Unintentional rotation below 10% PWM setting is therefore impossible. In addition, we also have the curve shown below.
Start-up and start-up behaviour with DC control
The following measurement curves once again illustrate the behaviour of the tested fan:
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