Bitaxe Gamma backstage: does size really matter?

In addition to cooling the ASIC processor, which is no longer a problem thanks to the currently best 52Pi low-profile cooler, the temperature of the VREGs plays an important role - chips that are too hot affect the functioning of the small home miner. However, this is not only due to the PCB heating up and thus also the incredible heating of the surrounding components, but also to a significant increase in power consumption. The cooler the VREGs are, the less energy the Bitaxe Gamma consumes, which is very expensive in many countries and also reduces the service life of the small miner.

With well-thought-out and coordinated cooling concepts such as the OC'axe, various tests have confirmed that good cooling not only increases performance but also significantly reduces power consumption. In the best case scenario, it is therefore not very wise to run the Bitaxe with the standard fan.

There are many different coolers on the market that can be attached to the hot VREGs. Aluminum is actually the simplest and cheapest option here, even if it is not as effective. The next step would be a copper heat sink, but these are also difficult to obtain if a specific and, above all, effective geometry is required. A copper cooler is not always a good idea, as it is too thick and the fins are too small, causing heat to build up and preventing the active air flow from cooling the cooler quickly enough. This leads to the formation of a thermal layer with this type of cooler, which actually impairs cooling.

Many people use the small RPi copper cooler sets; they are inexpensive and easy to obtain – but they cause exactly the problem mentioned above. The cooling performance is not really good due to the geometry; a more delicate aluminum cooler provides significantly more relief.

Copper coolers with a base plate of 2-3 mm and as many thin fins as possible between 10-20 mm are ideal. This guarantees perfect and fast heat absorption from the hot chip and extremely fast heat dissipation via the many cooling fins.

These small and versatile coolers, regardless of whether they are made of aluminum or copper, have one major problem. They have to be glued on – depending on the quality of the adhesive film, this forms a thermal insulation. Furthermore, the quality of the adhesive is also important; if it is poor, the heat sinks tend to fall off. Considering that even with active cooling, the VREGs can reach temperatures of up to 80°C, this is very annoying. The only solution is to turn the Bitaxe around and look at the back of the PCB – but this is usually not very attractive.

There is also another problem: on the back of the PCB there are four very small, very round and very hot chips. Attaching a heat sink here would be nothing short of a miracle. Normally, it would be possible to attach a heat sink to this spot using thermal adhesive, but most thermal adhesives have extremely poor thermal conductivity. It's certainly better than nothing, but it's far from ideal.

The Solo Mining Co from the beautiful UK has dedicated itself to this problem and has actually developed a solution that is second to none. That's how I received two more prototypes that make cooling enthusiasts' eyes light up.

We have three models for effective cooling of VREGs, suitable for any conventional Bitaxe Gamma layout. At first, I naturally focused on the two large prototypes and smiled a little at the small black magic cooler.

What makes all three versions special is that they can be mounted on the PCB using a physical fastening option. This eliminates so many mounting problems right away and even allows for further optimizations. For example, instead of using a thermal pad, you can use thermal paste with significantly higher thermal conductivity, but more on that later.

Here are some technical data to give you an idea of what we are talking about.

I've already tested a lot of coolers on the Bitaxe, but the “Bitchin' Sink” was still missing from my collection. In fact, I even got the new “mirror polished” version... Which is truly a feast for the eyes. So, in addition to the VREG, which is actually a problem child, I was also able to test the ASIC cooler in combination with the “Black Magic” fan.

Technical specifications are, of course, a must: an excellently crafted cooler with an M3 thread instead of four holes, making it very easy to attach. It also weighs an impressive 51,3 grams.

How do you compare a new and innovative cooling solution when there has been nothing like it before? I decided to use my custom build, which I use for many of my tests. A Bitaxe Gamma from PowerMining (like 90% of my miners), so I can always be sure that the quality is first-class.

The Gamma is connected with 14 AWG cables that are soldered in place. Furthermore, this custom build is equipped with all the necessary copper heat sinks on the underside, on the top of the PCB as well as on the underside. A copper cooler with thermal adhesive was attached to the four small, round, and very hot chips.

The ASIC is cooled with my Low Profile Plus cooler, which has three copper plates in a pyramid configuration. No thermal paste was used, but instead Indium TIM with a thermal conductivity of 86 W/mK. To put it simply, it is probably the best-optimized Bitaxe Gamma I have ever seen and has already passed extreme performance tests with an average of up to 2.5 Th/s. Admittedly, this is not entirely fair to the “Bitchin' Sink,” but the aim is only to test the underside of the PCB with the VREGs.

For this reason, subsequent tests with a Low Profile Plus showed higher ASIC temperatures. Yes, a proper setup really does make a difference of up to 10°C. Now my secret is out.

Since I also lack test series with the “Bitchin' Sink,” a test series was started here as well to see how well the combination of the two works. Thermal Grizzly Kryonaut extreme was used here as thermal paste to create an optimal connection between the ASIC and the cooler (also in the later test with the Low Profile Plus).

The fan used with the Low Profile Plus was, of course, the Noctua NF-A6x15 5V PWM fan, which is the absolute best choice.

For the cooling concept, I naturally opted for the OC'axe as a holistic cooling solution, which is simply first-class and unrivalled.

Although there were only three different VREG coolers and one new ASIC cooler, the tests were quite extensive. This resulted in some very informative test series.

Later, the test winner among the VREG coolers was also subjected to an extreme test, 1000 MHz, in OC'axe, which corresponds to 2 Th/s on a Bitaxe Gamma. One thing I can say for sure is that I was really surprised by the result.

The benchmark series is structured as follows: Test with the “Bitchin' Sink” ASIC cooler with the maximum possible overclocking within AxeOS of 625 MHz. The second test was carried out with the maximum possible clock frequency.

It was particularly interesting to observe how important good VREG cooling is and that it has a significant impact on both the possible overclocking and the power consumption.

The same test series was later carried out with all three VREG coolers in combination with a 52Pi Low Profile Plus cooler, once at a frequency of 625 MHz and once at 1000 MHz. My over-optimized Bitaxe Gamma setup was used as a reference comparison.

So let's start with the fun part. I would like to note that I have tested everything, but I tried to do so as realistically as possible. Not everyone optimizes their setup as extensively as I do, so improvements are definitely possible. Whether through the use of self-locking screws, thermal paste, even better thermal pads, or the ambient temperature... nothing is impossible.

Test series with the “Bitchin’ Sink” cooler; the first test reflects the raw performance of the cooler without VREG cooler. The subsequent tests were each conducted with a variant of the VREG cooler.

Can you see it? Yes, exactly... That's exactly how I looked at it. The question of all questions seems to have been answered: size is NOT everything! In fact, I am extremely surprised by this little wonder cooler, which weighs just over 3 grams.

To demonstrate its outstanding performance even more clearly, we naturally had to carry out an extreme test at a frequency of 1,000 MHz. Of course, we used the 52Pi Low Profile Low cooler, pitting the little black magic cooler against my heavy copper setup.

Yes, the cooling performance of the small miracle cooler is actually on par with a custom-built copper cooler. No joke, I checked it several times and observed it over several days. These three grams of aluminum, with their perfect fit, simply played the game to perfection.

I Am GPIO has actually achieved not just a small miracle, but a HUGE one. 

It shows that size is not always the decisive factor, but rather geometry and perfect workmanship. With 3 grams of luck and a physical connection to the hottest areas on the back of the Bitaxe Gamma PCB, the cooler is on par with custom builds, even if they are made of copper.

I already explained why above: there is no adhesive film that forms a thermal barrier. Instead, there is simply a good connection between the VREG cooler and the VREG with a good thermal pad. The cooling performance could certainly be optimized here if thermal paste were used.

I have also now tested the “Bitchin' Sink,” which really impressed me. The combination of three parts, such as the ASIC cooler, quiet fan, and VREG cooler, provides The Solo Mining Co with a perfect symbiosis – even overclocking outside the AxeOS specifications is possible.

Yes, my custom copper setup is slightly better. However, considering how much effort I put into it, including applying the thermal adhesive, it's not really an alternative unless you want it to be absolutely perfect.

But that's not all: in my opinion, the small miracle cooler is an absolute MUST HAVE for everyone, really! No more hassle with coolers falling off, perfect connection and workmanship.

Can it get any better?

I think so: if the small miracle were combined with the medium prototype. And if there were also a copper version, that would be absolutely amazing.

Presumably, even higher overclocking could be achieved without any problems with extreme custom setups. Or alternatively, simply run a very quiet Bitaxe Gamma. Especially since we are just before summer and probably not all setups will achieve 2 Th/s with the builds that work well in winter.

@I Am GPIO – Thank you for this innovation, you have achieved something that is second to none!

Now I only have one problem left: where can I get 27 pieces for my gamma swarm :)