Endorfy Stratus 140 PWM: Low price, high efficiency

The cheapest 140mm fan we’ve tested so far beats even significantly more expensive 120mm models at comparable noise levels. That’s because of the use of a larger cross-sectional area, as well as the efficient impeller geometry that the Stratus 140 PWM definitely has. “Cheap” fan doesn’t necessarily mean “weak”, though of course there are some compromises based on more limited manufacturing resources than with more expensive fans.

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 intensity.

…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.