Arctic S12038-4K: Massive fan for harsh conditions

A totally different type of fan than the ones we normally deal with. The Arctic S12038-4K is designed for high-performance servers, which is also reflected in its features. Very high airflow is provided by as much as 4000 rpm. And in order to ensure that the cooling performance does not drop significantly even through obstacles, the “extreme” Arctic fan has a profile that is as thick as 38 mm.

How we measure power draw…

Is it worth addressing the power draw of fans? If you have seven of them in your computer (three on the radiator of the cooler and four for system cooling in the case) and they are also backlit, the power draw starts at tens of watts. This makes it worth dealing with.
All fans are powered by Gophert CPS-3205 II laboratory power supply. It is passive and virtually noiseless, so it does not distort our noise level measurements. However, for the PWM fans, a Noctua NA-FC1 controller is connected through which the fans are regulated. We also have a shunt between the power supply and the Noctua controller. On it, we read the voltage drop, from which we then calculate the current. However, the voltage on the power supply is set so that 12 V goes to the Noctua NA-FC1. We then also set the exact 12 V to measure the maximum power of the 3-pin linear power supply fans.

In the power draw tests, we will be interested in the power draw in fixed noise level modes in addition to the maximum power consumption at 12 V or 100% PWM. That is, at those settings at which we also measure other parameters. Finally, in the graphs you will also find the power consumption corresponding to the start-up and minimum speeds. The difference between these two settings is that at start-up speed you need to overcome the frictional forces, so the power draw is always higher than at minimum speed. At these, the fan is already running and just reduces power to just before a level where it stops.

These start-up and minimum power draw data are a substitute for the start-up and minimum voltage information. You often encounter this when reading about fans, but with PWM fans there is no point in dealing with it. And although it is possible to power a PWM fan linearly, it will always perform better with PWM control – lower starting and minimum speeds. Therefore, it would be unfair to compare these parameters for all fans using linear control. That way, fans with PWM would be disadvantaged and the results distorted.

…and motor power

In addition to power draw, it is important to consider one more parameter that is related to the power supply – the power of the motor. This is usually listed on the back on a label and is often mistaken for power draw. However, the voltage and current indication here is usually not about power draw, but about the power of the motor. The latter must always be well above the operating power draw. The higher it is, the longer the life expectancy of the fan.

Over time and with wear, fan friction increases (through loss or hardening of the lubricant, dust contamination or abrasion of the bearings, etc.). However, a more powerful motor will overcome the deteriorating conditions of the fan to some extent, albeit at a higher power draw, but somehow it will cope. However, if the difference between the motor power and the operating power draw of a new fan is small, it may no longer be able to exert sufficient force to turn the impeller under increased friction due to adverse circumstances.

To test the power of the motor, we set the fan to full power (12 V/100 % PWM) and increase the mechanical resistance by braking the impeller in the middle. This is a higher load for the motor, with which the power draw naturally increases. But this is only up to a point, until the impeller stops. The power of the motor in our tests corresponds to the highest achieved power draw that we observed when the fan was being braked.

We use the Keysight U1231A high sample rate precision multimeters to analyse motor power (as well as normal operating power draw). In addition, the individual samples are recorded in a spreadsheet, from which we then graph the maximum. The final value is the average of three measurements (three maximums).