They are out there, but I just can't find them. I am intending to knock a couple holes in my cabinet and mount two 120mm fans (one intake at the front door, one exhaust at the rear side) for the server compartment, as the new hard disks are creating enough heat that the system overheats and reboots.
I found USB fans from Thermaltake (at Newegg), but the prices are nuts! $24 for essentially a $3 fan.
I've been messing around, and have found that even multi-speed 12V fans won't start without around 7-8V input, so either I am building an external molex socket, or I need some other fan I can power via USB.
Ugh, so expensive! Turns out a couple 12V fans and a 12V power converter will have to do the job. I just can't justify $40 for what I can do (less neatly) for $10.
Impressive fans. If this was a PC build, this likely would be the way to go, and I will be adding those to my wish list for the next machine build for sure!
However, in this case, all I need is a low draw, quiet fan to keep hot air from building up inside the cabinet, as when under load the server has had some extreme temperature issues as the weather has warmed up. The system is essentially a file server, but with the FTP/HTTP functions for remote access (I load pictures to it by remote via my laptop and a cellular link when I am on the go) I have managed to push the temp to a blistering 55°C in AIR TEMP, and that is what is cooling the hard disks and CPU.
It stinks when the system shuts down due to thermal stresses while I am on the go. What makes it even worse is that FreeBSD Server/FreeNAS doesn't currently have an auto-shutdown routine available (that I can find, anyway) and I have to go through volume verification when bringing it back up... which means scanning through terabytes of space, and LOTS of time.
A couple fans pushing a measly 20CFM in then out would prevent this from happening.
Those lead adapters acts just like an inline resistors. I don't know but it's worth a shot to try to wire a resistor with enough ohms to reduce the voltage to 5. Or better, see if anyone sells leads that converts into 5V.
Most variable resistor adapters convert between 6-7V to 12V, which makes sense because a lot of the higher quality fans have a "kick rate" of 6-7V, essentially the blades won't begin oscillation until the motor sees this much juice.
This isn't at all what I need, though. What I wanted was fans that could be easily adapted to USB for power, for the purpose of centralized power switching (server off, fans off), but in afterthought the server is always on, so I shouldn't be picky about the fans' power. An external 2A molex PSU will do what I need and not cost an arm and a leg to power.
i would find a cheap laptop cooler that uses usb and take those fans
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