So these servers I got are insanely loud, and I can’t stress insanely enough. The fans don’t seem to spin down to any reasonable level even when nothing is stressed and the system as drawing a “paltry” 650w.
So since there’s no direct control of the fans, at least so far in my limited testing with FreeBSD which I’m unfamiliar with anyhow I decided to quiet things down the hardware way. I took each of the 6 120mmx120mmx38mm fan cages out with *65dB* fans rated at 150CFM and cut the power cables to the proprietary connector. There was no way to get a standard width fan in here easily, so I decided to try running each pair in series.
That didn’t go so well. The fans would spin up a bit and then spin all the way down, the server thought they were bad. 6 volts was not enough to keep them going.. so I decided to cheat another way. I cut the power wires to some of the remaining 4 and wired a few diodes in series (5 of the 6 fans have 2 diodes, one has 3). That should give me some voltage drop from the forward bias of the diodes, and it did! My system went from absurdly loud to manageable.
For the other server I’ll be trying 4 diodes in series to try to get a bit more Vdrop and a bit more manageable noise. So far, so good. The 1.5amp diodes aren’t quite enough for my 150CFM Deltas and managed to burn out. 4x 3 amp barrel diodes fit perfectly in the little cavity in the fan, but I don’t have any pictures to show of that at the moment unfortunately.
Twist the diodes together, anode to cathode (note the silver band), this will get us some voltage drop.
Solder these connections and clip the parts we just soldered, we just need the two ends. This step is basically the same for 4 diodes, you just cut one more twisted set.
If your fan has a cage, disassemble the fan from the cage. Mine had plastic push pins much like most cars do, after that it slipped right out as I spread it apart to take the custom connector out.
Place the diodes on the fan, you can use some super glue to hold them in the cavity if there is a cavity. Otherwise place them somewhere convenient. Tin the anode/cathode of the diode(s) and cut the main power wire to the fan. Tin those wires.
Solder the power wires. The incoming wire will be wired to the cathode, or to the diode with the band furthest away from the connection.
You should probably have used shrink wrap in Step 5 (doh!), use some electric tape to make sure the exposed power does not hit ground and short out. (Yes, I had this problem, even with the electric tape, and I had to do horrible things to get the fan going again since it uses an uncommon connector that I couldn’t just replace)