spec'ing out motor for DIY high quality desk fan?

[andrew.box]

I'm tired of wasting money on small fans that fail in one way or another after maybe a year or two. I'd like to try and build a desk fan using a high grade automation or servo motor, possibly variable speed DC drive but whatever allows good speed control.

Anyone want to help me design the project, starting with choosing a nice motor with long projected life span? I've looked around at motors but there are just SOOO many options, it's hard to pick.

Let's assume for now price isn't an issue, within reason, i.e. I'd spend $300 maybe more for the main components if I end up with a "buy it for life" desk fan.

 

[john61ct]

The "computer fans" that go into industrial racked servers are designed to run many thousands of hours, move a lot of air turned up, and speed can be well controlled via PWM.

The one factor hard to find out about before ordering is noise, but they are cheap enough to mean trial & error is not out of the question.

The PC enthusiast subs can help ID in advance the whisper-quiet larger-diameter less-robust not industrial-class ones, also effective and pretty cheap, but you may be replacing those every few years.

 

[amberwolf]

I'm afraid I don't know enough about industrial motors to help pick one out of the thousands (more, really) out there.

Regarding the server fan types, I have a pair of Papst typ 6448 / 2hht fans that have lasted for years so far, and who knows how long they were used before I got them out of some rackmount something-or-other from a junkyard (just had to clean the dirt off of them).

They are spec'd to run off 46.5-49.5vdc, which has been handy since getting into ebikes, since they'll run off an ebike pack ok. (I've actually run one of htem for hours at a time off a 14s pack that was around 56v when I started, and it didn't blow up or overheat, etc, during a power failure when I had to have a fan to keep cool. Still using that fan even now, powered off a 36vdc wallwart to help a window AC unit move more air....).

They have a "program" wire (which is probably a voltage input to tell it how fast to spin, but I've just tied it to ground to run at full speed; I never looked up the specs to check on it), and a tach output wire (whcih I don't use).

Unfortunately it is kinda loud...but it moves a hell of a lot of air. It's quieter without the cage around it, but not quiet enough if you need a "silent" desk fan. It might be better if using the "program" line to change it's speed to something slower. (it *is* a lot quieter at the 36v...)

I suspect the motor itself could be used to drive a larger diameter fan blade (that is very well balanced) at the slower speed without nearly the same noise.


The main problem I find with most "desk fan" (or other household fans) is that they don't use bearings in their motors. They use bushings.

If you were to take the bushings out and replace them with sealed bearings (to keep dust out) and ensure they were properly and regularly lubricated as needed, the household types would last a lot longer (however long the bearings are designed for).

I have a box fan that's reaching the point of bushing failure, that I am likely to see what bearings I have laying around out of something else that will fit in there.....

 

[Dui ni shuo de dui]

I was thinking about doing something like that a few months ago, but much bigger.
The idea would have been to build a gigantic fan, maybe 2 meters in diameter, powered by a rewired scooter hub motor and a sinewave controller.

The fan being very large, it would only have to turn at extremely low rpm, so I could install it in my bedroom and get fresh air without any noise.

For your project, since it would be way smaller, maybe you could go for a brushless motor from a RC car or airplane with an extremely low KV. Since it would run at very low power compared to what it would experience in a RC vehicle, I'm willing to bet that it would last a very long time. The only unknown would be the controller, I don't know how well those little things can stand daily use, but basically I suppose that since it won't really have to deal with abuse it should be fine.

I see many advantages of doing it that way: it's very cheap, it 's probably reliable since it's way overpowered, it should be fairly quiet and you can even remote control it if you ever want to
The inconvenience being that you will need power supplies to feed the correct voltages to the various components.

 

[Dui ni shuo de dui]

If you were to take the bushings out and replace them with sealed bearings (to keep dust out) and ensure they were properly and regularly lubricated as needed, the household types would last a lot longer (however long the bearings are designed for).

I have a box fan that's reaching the point of bushing failure, that I am likely to see what bearings I have laying around out of something else that will fit in there.....

I'm really no expert so I might be wrong, but from my experience bushings are way quieter than bearings. It could be the reason why they are using these.

 

[flat tire]

They have some pretty large fans, like 8" or more for PC cases that move a lot of air quietly. The motors are all brushless and usually last thousands of hours. They are inexpensive. Don't reinvent the wheel.