Quote from: dslr11 on May 30, 2018, 07:25:27 AM

For those interested in the details, the latest S9s have slightly different fans front and back. I have no idea WHAT the difference is, but the front fan is NIDEC UltraFlo W12E12BS11B5-57 and the back one is NIDEC UltraFlo W12E12BS11B5-07 (note the last two digits). Both are rated 1.65 Amps and I see no visible difference between them. But if they took the effort to install two different fans in each unit (which means more complicated logistics), I'm sure they have a good reason for it. I can't find specs for the fans anywhere. If anyone has any info (or even a theory) about the reason for the different fans, I'm curious. Maybe different RPM at the same voltage to make it possible to feed them the same voltage and still maintain the slight pressure difference?

Bitmain uses whatever cheap fans they can source locally at the time. I would say I have at least 8-9 different fan types in my datacenter. They also are not always the same amperage either, the quality and specs can vary pretty wildly and i have confirmed some major flow differences between models. The only criteria i have seen is the rpm range, they need to be able to reach 6000 rpm because that is what the firmware expects and changes voltages to change speeds based on that assumption.

So there is no big mystery. Its just a company buying a disposable part from the cheapest vendor whenever they order. There is no secret or special reasoning for it.

P.S. After attempting to translate what the OP was talking about, it looks like he could have fixed his problem just by flipping one fan around. Yes sometimes from the factory they are backwards, sometimes from the factory they are plugged in backwards on the controller as well. Its not a big deal and certainly not worth complaining about, it takes less than 1 minute to flip a fan around and doesnt touch the warranty stickers.