After many many hours of investigation i finally managed to undervolt a Z9 mini.
Power usage can be as low as 13.5Watt/Ksol at the wall(power meter) with a platinum power supply and this was a z9 mini batch 2, so all other batches should perform slightly better.
I get 10Ksol with only 138W, which is almost 50% less power comparing to official specs.
Undervolted Z9 mini, can be made silent, with 2 x under 20db fans and a fan simulator
Same performance/watt can be reached on Z9
More details of my tests below
Stock performance
Frequency | Watt | Ksol | W/Ksol |
700 | 363 | 15.3 | 23.7 |
600 | 311 | 13.1 | 23.7 |
500 | 259 | 11.5 | 22.5 |
400 | 210 | 9.3 | 22.6 |
Undervolted
Frequency | Watt | Ksol | W/Ksol |
700 | 321 | 15.2 | 21.1 |
600 | 237 | 13.0 | 18.2 |
500 | 173 | 11.5 | 15.0 |
400 | 126 | 9.2 | 13.7 |
I'm not sharing any how to details because my solution, at this stage, requires additional tools and is too difficult
The software solution will be much better if it can reach the efficiency above.
I've tried playing with the Antminer L3+ solution
https://bitcointalk.org/index.php?topic=3546316.0but there is no "/dev/i2c-0" file on Z9 mini
Anyone with more knowledge, please share your thoughts on how to get access to those chips through i2c in a similar way it was done for L3+