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.

The fan’s currently in the switch are:

He suggested if this fan would work as a replacement:

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.




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