This is a first – a fan with the leading edges of the impeller blades on the opposite side to normal ones. This is primarily done for a better view of “fans without stator struts” in cases with glass side panels. In addition, such an unconventional design also has quite clear and measurable advantages and disadvantages, also in terms of functional characteristics. Let’s take everything in turn.
Initial warm-up…
Before we even start measuring anything, we let the fans run “idle” for a few minutes after plugging them in. This is because immediately after a cold start the fans reach different parameters than after a certain amount of short-term operation.
Until the operating temperature of the lubricant is stabilized, a typically lower maximum performance is achieved. This is because at lower temperatures the lubricant is denser, which is associated with higher friction. Therefore, the fans do not reach maximum speed immediately, but only after the first few seconds. Before the first measurements, we therefore leave the fans running for at least 300 seconds at 12 V, or 100 % PWM duty cycle.
… and speed recording
The speed of the fans is monitored using a laser tachometer, which reads the number of revolutions from a reflective sticker on the impeller. For this purpose, we use the UNI-T UT372 device, which also allows real-time averaging of samples. Thus, we do not record the peak value in the graphs, but the average speed value from a 30-second time period.
However, the speed itself is a relatively unimportant parameter that is often given more attention than is appropriate. This is the case even in many fan or cooler tests, where speed is used to normalize the different modes in which other variables are measured.
However, hyper-focusing on a specific speed is a rather unfortunate decision if only because the fans don’t gain any commonality. At the same speed all other variables are different, there is no intersection. It can be noted that a better normalization would have been by any other variable, whether it be static pressure, flow or noise level, which wins in our case. But more on that in the next chapter.
We only measure the speed so that you can associate a particular parameter (such as the amount of static pressure or some noise level) with something according to which you can adjust the fan yourself. Perhaps for that alone, the information about the achieved speed is useful. As part of the fan analysis, we will also indicate what the fans’ starting and minimum speeds are. Start-up speeds tend to be higher than minimum speeds because more force is required to get the impeller moving than once the fan impeller is spinning, and a minimum power intensity is sought at which the fan does not stall.
That’s unexpected results. I would have guessed it performs better on radiators than vs no obstacles, but it’s the opposite!
Is the buzzing noise only present under ~750 RPM, or is it there across the whole speed range? On higher dBA settings, I can still see some of the peaks at 1-2 Khz.
There will probably be some buzzing at higher speeds, but because of the diminishing contribution to the total, in contrast with the aerodynamic noise (which drowns out these sounds) it fades out alongside other, significantly noisier frequencies. The buzzing is, of course, more pronounced at lower speeds (like ~750 rpm), at the limit of minimum rpm. But we don’t have a spectrogram for those. 🙂
Noticeable buzzing noise is present till the 20% of PWM or ~660RPM, have three of those on a 45mm rad :/
I mean buzzing is starting from 20% of PWM and 660RPM, and after 800-900RPM buzzing noise doesn’t bother because airflow noise is louder.
Little correction 🙂
Thank you for sharing your user experience. Yes, the buzzing noise also occurs at higher speeds, and the question is to what extent it is disruptive at which speed compared to the aerodynamic noise. This can be evaluated differently by everyone, as it is subjective.