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, to be on the safe side, we check the maximum speed at 100% PWM and compare it with the datasheet. The fan easily manages the specified data and even surpasses it slightly.
In today’s test, we see that once the fan has started up, it can handle low voltages starting at around 2 volts, while Blacknoise’s fan requires at least 3.3 volts. Furthermore, 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 and the 7V DC adapter is all the more surprising.
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%.
Start-up and shut-down behaviour
The following measurement curves once again illustrate the very different behaviour. Let’s look at DC control first. Here the 174 rpm minimum speed is reached at approx. 2 volts, which is even slightly below the values of the data sheet. The fact that the fan then still rotates, but no longer produces any effect at all, is another matter,
However, PWM control stops just below 500 rpm! You can set whatever you want, the RPMs will NOT drop any further and neither will the specs on the data sheet. The fan stays at 477 rpm, but does not go off either. With which one must really question the sense of this PWM control. 3-pins would have been enough, this is rather pointless in this form.
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