On ebay are offered used fan with DC motors from 13 euro, which with up to air flow: 225 m³ per hour with a maximum of 45 watts have very good performance values.
For me it was important that it is possible to regulate the speed of the fan, because I don’t always need full power.
In the reviews of the product below in the auction, it was announced that the speed of the motor can be controlled by PWM.
This data sheet of an almost identical fan shows on page 4 that it is possible to control the speed via a PWM signal. With my fan this doesn’t work.
After many attempts to create a PWM signal and to pick up a speed pulse, I decided to take the fan apart.
Inside it is not a normal DC motor, that is more a microcontroller-controlled high-tech product. I am sure that the circuitry would allow speed control even if for that the internal fan microcontroller’s code would have to be adapted.
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