Intro: Make a Workbench Fan From an Old Microwave Oven Exhaust Fan
I always like to salvage usable parts off of things before I recycle them. So when replacing a microwave oven, I salvaged the fan and starter capacitor.
I found this two-speed fan to be quite-powerful (300-400 cfm), and directional. Which gave me the idea of making a fan for my workbench that blew across a zone a foot above the work surface. This way, dust and paper are not blown all over the place, like with a conventional fan.
Step 1: Parts
- You will need the fan and motor capacitor from the old microwave. Salvage any mounting screws you may need also.
- Look at the motor schematic, usually on a label in the oven chassis. Try to find the wattage and note the required circuit design (capacitor, hi/low settings, etc.).
- Find a salvaged power cord with compatible polarity and wattage rating.
- Figure out a way to make a stand. Understand how the motor needs airflow to stay cooled.
- Get some salvaged rubber feet (like form old electronics components) for the base.
- You will need some plastic to cover parts of the motor for proper air flow and safety. I used some heavy scrap black plastic from flexible landscape edging. I screwed it in using the alternative motor mounting screw holes.
- If you want to maintain the Hi/Low/Off function, you will need a switch that can do that. If you are happy with one speed, any wattage capable, regular AC 120 volt switch will do. I found a toggle switch with Hi/Low/off for about $3. This was the only part I had to purchase. Get help if you are not familiar with safe electrical wiring.
- I used a salvaged plastic electrical box to house the connections, capacitor and switch safely. I opened the knock outs in the box to allow air to cool the parts and flow over the motor, thru a hole in the stand.
- My design is not kid friendly. Little fingers could get in the electrical box and there are exposed fan blades.
- Important: Clean off all of the grease from the fan blades. I used a citrus-based cleaner in a spray bottle. This is a pain but necessary for efficient operation and to avoid fires: Grease plus shop saw dust is no good.
Step 2: Understand the Airflow
Study the picture to understand the airflow of this fan.
It is important that your design provide air to the inner part of the separated fan. This section of the fan pulls air over the motor to keep it cool. The red arrows show how this design leaves over eight holes as air inlets for the motor side of the fan.
Most of the air enters from the top and bottom of the fan, via the outer portion of the fan blades.
Side note: Seeing this separated fan design made me realize my microwave fan was 33% motor cooling (and cooling for parts in the microwave itself) and only 66% exhaust for the cook top under it.
Step 3: Put It Together and Paint It
You are pretty much on your own here. See pictures for what I did. Sorry I don't have more photos, but I made this a few years ago.
You get a nice, strong, directional wind-flow that can be aimed by rotating the base. I blow it across the front of my 11' long work bench, so that the entire length has a breeze. I love this thing.
For $3, not only is the price right, but it's better, for this workshop purpose, than anything I could buy. My High Velocity Patton fan moves a lot of air, but blows up a storm, so I cannot always aim it at my work bench.
Enjoy the breeze.