775 motor duct fan, range hood, fresh air system fan, vacuum fan, exhaust fan

Design Highlights

• Excellent exhaust efficiency, with higher static pressure than a 4-inch fan I bought for over 100 (yuan). The inlet and outlet outer diameter is 96mm, which is convenient for connecting 100mm flexible ducts. My tests show that any larger would make it difficult to connect.
• Low energy consumption. I measured it, and it's over 50W at full load, which is very powerful but also very noisy. It depends on your usage needs. I prefer fan speeds with power consumption under 20W. The fan I bought didn't have speed control, and its power consumption constantly fluctuated around 50W.
• Duct-style horizontal structure with clear inlet and outlet directions, suitable for connecting flexible hoses or nozzles.
• Integrated desktop base provides stable placement, unlike temporary assembled parts.
• Trapezoidal support connects the fan housing and base plate, providing balanced load-bearing and aesthetics.
• Black industrial design, making the whole unit look more like a finished small device.
• Switches and speed control knob are centralized on the front for easy operation.
• Reserved pipe interfaces at both ends for convenient future connection of flexible hoses, filters, or adapters.
• Reinforcement rings on both sides of the fan housing enhance rigidity and conceal splicing/assembly points.
• Electrical controls are concentrated in the base area to reduce exposed wiring at higher positions.
• Clear modular design, allowing for easy individual revisions of the fan housing, base, nozzle, motor, and impeller.
• The structure is suitable for FDM 3D printing, primarily composed of cylinders, bevels, flat surfaces, and reinforcement rings.
• Unified appearance and function; the support base, bottom plate, control panel, and fan housing form a complete design.

This version took a long time to develop, and I even delved into the principles of impellers along the way. Of course, there are many imperfections. If more people use it, I will continue to optimize it, and I will also create a wall-mounted version. You can leave comments if you have any adjustment needs or installation questions.

Parts List

775 motor, 10-15 yuan
24V power supply, around 10 yuan 
PWM speed control module, around 4 yuan 
Small boat-shaped switch, 0.3-0.5 yuan each
Power plug, around 1 yuan
Fuse holder (preferred, if not, directly use washers and screws to fix the fuse in the screw holes on the base plate, these holes can also be used for cable management), 0.5-1 yuan
T5A slow-blow fuse, 0.5-1 yuan
M3 screws: 4 pieces with thread length 12 or 14, 3 pieces with length 10, 4 pieces with length 8, a few cents each
M4 screws: 2 pieces with length 10, a few cents each
I used 1.5 square mm two-core wire, around 1 yuan 
Heat shrink tubing (buy according to wire diameter, mixed packs available), within 5 yuan
Anti-slip feet *4, within 0.5 yuan

All of the above can be purchased on Pinduoduo or Taobao.

The total cost is estimated to be just over 30 yuan, mainly because it's quite fun to make it yourself.