OC'axe: let the wind chimes begin

Right after the first prototype of my OC'axe development, the question arose as to which 120 mm fan would be suitable for this concept. At that time, I tested a variety of different fans, including a 120 mm model. Although the first OC'axe prototype was far from having the optimal airflow geometry, the winner was quickly found: Noctua NF-F12 PWM. I used this fan for all my tests during the development and optimization of the case for the Bitaxe.

But now that the final and almost perfect geometry has been found and the first public Alpha OC'axe versions are already in circulation, the question naturally arises again: “Is the Noctua NF-F12 PWM still the right choice?”
This time, to really cover all eventualities, I also took other fans that are not compatible with the OC'axe, but it would be nice to know if they can significantly increase the cooling performance of the Bitaxe.

The selection of 120mm fans that are designed for a voltage of 5v is actually very limited and can be counted on one hand. So I had to think of something here and immediately reached for 12v models. Of course, you wouldn't be able to get the full power out of them if they were running on a 5v power supply. So I took the excellent Mean Well LRS-150-12 PSU, created an adapter from a Noctua extension cable so that I could connect the fans directly to the PSU. This way, the fans all ran at 100%, which is perfect for our test series.

The product description for VBESTLIFE is witty at its best: a low noise level of 70 dBa makes it possible to blow very quietly. The dealer really has to have a sense of humor.

All fans were attached to the OC'axe, but the case was not assembled for test purposes. A Bitaxe Gamma from PowerMining was used for testing. I just love the manufacturing quality and the stability of the devices during overclocking.

PS: Did you know that you can save 10% on all orders at PowerMining with the code “OCaxe”? Now, at the latest, there is no excuse not to stack even more hash power. 

All relevant areas were covered with copper coolers and optimized so that the cooling performance works as it should. The test was carried out with the Low Profile Plus and a Noctua A6x15 PMW 5V, currently the best combination for ASIC cooling. Thermal Grizzly Kryonaut Extreme was used as the thermal compound. The Bitaxe Gamma itself was operated with the Mean Well LRS-70-5.

To cover all eventualities, the Bitaxe Gamma was used with solidly attached power cables, with 12 AWG cable thickness. The Bitaxe Gamma was operated at 1,000 Mhz at 1,300v, the fans were set to 100%.

40 or 60 mm fans, which are usually used in the community to cool the back of the PCB, are okay but by no means optimal. Often I see that the fans are positioned incorrectly, which makes things even more difficult and reduces performance. Many people don't know or think about the fact that every fan has a dead area in the middle and thus produces no air movement at all.

So if you position the fan directly above the chip to be cooled, the cooling performance is significantly reduced, but a certain angle of incidence is also very relevant... Which is not taken into account by many at all.

With the OC'axe, you have several advantages here compared to small fans. A 120 mm fan is used, the entire air flow is directed and compressed by the casing. This breaks up the dead center of the fan and combines it into a new air flow. The PCB receives the entire air flow at the right angle and is perfectly cooled.
 

The results of testing the different fans are really interesting. Certainly, 38 mm high speed fans are the leaders in cooling performance. However, they are so loud and power hungry that they are not suitable for use here at all. But it is interesting to see what is possible and how the cooling performance compares to the usual Noctua fans.

As with my first test, the Noctua NF-A12x25 PWM is and remains the clear favorite and reference for perfect cooling. In second place, I would put the Noctua NF-F12 iPPC 3000 PWM – but it is significantly louder. In terms of cooling performance, however, they are very close.

It was really a very interesting test, especially to be able to test the final geometry of the OC'axe. In winter, we rarely have thermal problems, especially when overclocking. Much more exciting is the summer or warm countries, where conventional optimization with a 40 or 60mm fan will most likely fail.

So when it comes to a holistic concept, the only way to go is with the holistic solution of the OC'axe.