Customizing USB Fan

About: Mechanics is the paradise of the mathematical sciences because through it you can reach the fruits of mathematics. Leonardo da Vinci (1452-1519)

Customizing USB fan

I needed a small USB desk fan. I searched for something quiet, consuming less than 1A and not expensive. The best option is in the first position of my part list. But it wasn’t quiet at all! On the contrary! The noise was so loud as the motor was assembled using bushings recovered from scrap. My first intent was to send it back. Then I remembered an old trick. I removed the propeller and using a pointed wood pin I added a little drop of hydraulic oil between the axe and the bushing. The little cheap engine become quiet! Only the aerodynamic noise produced by the propeller. Having a quiet fan, what if I would add variable rotation? Automatically adjustment mean to use temperature information and some volume outside the propeller cover. Manual adjustment mean just to install a potentiometer on the back of the cover. I choosed this way using a simple scheme with a transistor to supply the motor with almost all the input 5v tension. I also considered to use the fan with an independent power supply converting mains 240Vac to 5Vdc. Because these convertors are delivering Power, if the current is excedeed, the tension has the tendency to drop. That happens very often with the cheap devices that cannot deliver 1A as declared on their label and if the consumption is 1A for real, tension drops to 4.7 or even lower. Adding the fact any N-P jonction introduces a ~0.7V drop, finally the little motor could receive 3.5v. Not to much rotating speed because his technical data said about 3÷6V. As a result, I added a “drop-up” source. Please see the attached sketch with the electric scheme. Sorry it has such a poor look, but I have no ideea how to use Fritzing. The only available volume to insert the scheme was the central cilinder containing the motor. Outside, but still inside the propeller cover (offering air cooling), I assembled two 3D printed supports:

- first for the “drop-up” source;

- second for the display, transistor and his improvized cooler.

The electric scheme is too simple to require a PCB. Just connect the terminals. The values of components aren’t critical. To adjust the "drop-up" source:

- having an "USB Charger Doctor" would be good, to see what U/I comes out from the USB socket;

- rotate the fan potentiometer in the max position and live it like that;

- rotate the XL6009's trimmer increasing rotations until the converter tension suddenly drops. Note the value shown before that moment, by the fan's display;

- go back and redo the adjustment a little bit before that displayed value. This is the maximum that specific converter can give. Try not to overload the motor.

The cilinder needs few holes:

- for support 1: 2xø2 for screws, 2xø4 for wires;

- for support 2: 1xø2 for screw and 3xø1 for transistor (B-E-C), 1xø4 for display wires.

The cover back panel needs 1xø7 for potentiometer.

I attached some photos, sketches and a little movie. You can play the same way with any DC brushed motor.

Looking back, I bought a cheap thing and I invested three times his value in order to transform it in something different. But otherwise, where is the fun?

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