Antminer S21 Review: Examining the S21's Performance and Design

Bitmain unveiled its newest miner, the Antminer S21, at the 2023 World Digital Mining Summit in Hong Kong. 

The much-anticipated S21 series features the most efficient and powerful Bitcoin mining ASICs to date. Bitmain released two versions of the S21 at launch: an air-cooled version and a hydro version. At 200 TH/s and 17.5 J/TH, the Antminer S21 is the most powerful and efficient air-cooled Bitcoin mining rig available on the market today, and the Antminer S21 hydro is one of the most powerful and efficient ASIC miners in the water-cooled class of mining rigs.

In our most recent report, we review the Antminer S21's hashrate and efficiency performance, as well as its interior and exterior design. You can download the report below:

We also cover our findings in a two part series on the Luxor Youtube channel:

Antminer S21 Performance Review

Antminer S21 Design Review

Now, for the rest of today's newsletter, we'll cover a few of the report's key findings.

Antminer S21 Performance Test Results

In our test of the Antminer S21, we subjected it to a range of different temperatures. 

To start, we powered on the machine for 30 to 60 minutes until hashrate and power draw clearly stabilized. Then we inserted the rig into a temperature controlled box and tested it at a range of temperatures for 30 to 60 minutes: 10, 20, 25, and 40 degrees celsius.

The table below presents the real-time hashrate, power consumption, and efficiency metrics of the S21 at various temperatures. Notably, at 10 and 20 degrees celsius, the S21 operated at its advertised specifications. 

Another noteworthy observation is that the default firmware of the S21 tends to increase the PSU voltage in colder conditions and automatically initiate underclocking when the temperature approaches approximately 40℃ based on our testing. The specific temperature at which the S21 begins underclocking may vary depending on the environment, but generally, the range of 40℃ ±3℃ is standard for underclocking according to Bitmain.

We believe that this stock firmware feature gives the S21 its advertised operating temperature of up to 45℃. Furthermore, users have the option to adjust their voltage and frequency settings by utilizing third party firmware, such as LuxOS, if they wish to establish different thresholds for underclocking or overclocking.

Antminer S21 Design Review

The S21 series features identical dimensions to the S19 series (400*195*290 mm). However, the S21 exceeds S19 series rigs in weight by at least 1 kg, and it has a 5℃ higher maximum operating temperature threshold. The table below provides a comparison of the weight and operating temperature for the S21 model versus the S19 series.

The S21 will introduce a PSU variant first seen on S19j XP, the APW171215a. This power supply unit features an input voltage range of 220-277V and an output voltage range of 12-15V. Upon inspecting the PSU internals, we noticed that this PSU model incorporates 5 capacitors with increased voltages of 500V, surpassing those of the S19 series, such as the S19j Pro+, which utilizes 450V capacitors. These capacitors highlight Bitmain’s efforts to revise and improve their ASIC miners’ power supply design over time to help ensure power stability and capacity for overclocking, and the S21 will certainly benefit from these improvements.

For the full review, please download the report above, and feel free to give it a share and let us know what you think!