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Salvaged Circuitry

Adventures in Tinkering

Dorm Room Fan

The following page is a guide on how to make your own dorm room fan out of a blower from an old microwave. The blower features a 120v AC motor, an indicator light, a variac for adjusting the speed of the fan, an on switch and a C-14 connector for easy plug in.

Here's the fan after it was spray painted and cleaned. Since this blower came from a microwave, it wasn't at all clean. I spent more than an hour cleaning the blower housing and impeller blades with various cleaning agents. A small 1inch brush seemed to do the job for getting in between the blades of the fan, which were no more than .25 inch apart.

Here's a better picture of the blower assembly. The white metal bracket on the right side of the picture will be used for the mounting of the new motor, since the original shaded-pole induction motor unfortunately died during the construction of this project. Yes, this piece of metal is a 2U mounting bracket from a 2U battery backup unit.

With the new motor installed, the next most important thing was to make sure that the motor was straight with the blower shaft. Since the shaft sizes were slightly off, the shaft of the motor had to be sanded down and the blower shaft had to be widened. After filing and aligning the motor and fan assembly, I mounted the motor to a 1x6 piece of pine. I originally wanted to use metal as a base for the fan, however, that seemed like a bad idea since the metal base would rattle in my dorm windowsill. I'm sure my roommate would be less than happy about that.

From then on in, I decided to make the entire case out of wood. this would dampen the sound of the fan and lessen the rattle of the overall blower. I used bolts to fasten the motor to the wooden base and various pieces of steeltec to act as shims to enable a more steady spin of the blower.

Here's a closeup of the motor assembly.

Here's a side shot of the dorm fan in it's beginning state.

After a trip to get some 1"x8" pieces of wood, I constructed the case for the fan. The obnoxious dot in the front panel of the fan is an indicator light, green specifically. The case was constructed to a 32" x 8" x 6.5" footprint, and assembled with 1.5in drywall screws. The air ducts were cut out from the wooden shell.

With the outer casing mostly complete, I decided to incorporate a means to control the speed of the fan. Since I did not want to use any old potentiometers, I decided to go with a small scale variac. I also incorporated a replaceable fuse for more convenience.

Here's a top view of the innards of the dorm fan.

Besides the motor and fan assembly, I decided to add a small fan on the end of the motor shaft. I was concerned about the heat outputted by the motor, since the blower does not directly cool off the motor. In a traditional axial fan, heat is not of great concern, for the air forced through the fan blades cools the motor as the air passes from the front of the fan to the back of the fan. In this case, the fan blades are rotated 90 degrees in a blower, so internal heat is a problem worth considering. If the motor gets too hot, malfunction could occur. So, I took a small plastic fan from an old hair dryer and a rubber sleeve from a printer and attached the fan blade to the shaft. this way, as the motor spins it is also getting cooled.

Here is the variac, C-14 adapter and on/off switch on the final product.

The stain really brings out the grain of the wood, and should go well with the dorm windowsill (if it's stained)...

Here's a closeup on the inside of the fan. I left a 3.5in gap for the air intake so the fan would not be overworked from a lack of air input. I may decide to incorporate a metal grate over the input in the future, but for now this should do.

All in all, this project was quite a challenge. The blower assembly wasn't exactly easy to work with since it was cylindrical, and the death of the first motor made the project take longer than desired. Besides these setbacks, the dorm fan came out better than expected. Lets hope my dorm roommate doesn't mind an extra 50db to the airspace.