So this weekend someone asked me about an issue they had with the Cisco POE switch being very noisy. He sent me this link he found where a SysAdmin went and found replacement fan’s for his switch to quiet them down. http://wahlnetwork.com/2014/12/21/diy-project-replacing-stock-cisco-sg300-52-fans-silence/
The fan’s currently in the switch are: https://www.digikey.com/product-detail/en/delta-electronics/EFB0412MD-R00/603-1581-ND/2560704
He suggested if this fan would work as a replacement: https://www.digikey.com/product-detail/en/ebm-papst-inc/412-2/381-2459-ND/592230
After a brief look into the datasheet, I found that the current fan vs. the new fan did not have a “Tach” to read PWM to get a return value on how fast the fan is moving, it did, however, have a Stop Rotation Detection method through the third wire. In this case, the replacement fan he suggested would spur a large number of false positives for error’s as the line should only go HIGH when the fan is jammed verses every 1/10000 of a second for its speed. So I instead dug through my box to locate an L7808CV Positive 8V voltage regulator. I found 8V make’s the fan extremely quiet and kicks the speed down. I ended up testing it with my bench variable power supply before concluding the 8V was the value I wanted. I quickly threw together a board and hot-snotted the unit to the back of the SG200 and what do you know, quiet as a ninja and no fan alerts.