The pretext:
So I recently bought a Xiao Mi Air Purifier 2. From a hardware point of view its pretty good, but the App to control it doesn't work plus there are some concerns about privacy / data security. So I figured the best solution for me would be to write a custom software using an Arduino to control the fan. (without the App I am stuck with a 'full throttle' or an automatic mode)
The problem:
When I took it apart I found that the motor that drives the fan is not a simple DC motor as I would have expected. In fact it uses a 6 pin plug :o
I hooked up a multi-meter two the two thickest wires (which I figured would be the power supply) and found that the fan runs on a constant 24V DC. By constant I mean it gets 24V regardless of its power level / speed, so even when its turned off.
So my next suspicion was, that it was 'just' an current regulated motor. So I put 24V on it with my lab power supply and increased the current. However the fan did not turn, but at some point the whole system powered up. So it looks like that the fan is directly connected to the 24V power supply of the whole system and that it must be controlled with the other 4 wires someway or another.
I have no clue on how to drive such a fan. I searched for datasheets of 6 pin fans, or constant voltage fans but found nothing.
Any suggestions on how to identify or run such a fan or the next steps?
Its likely a brushless motor (silent, long life - standard DC motors are noisier and the brushes wear out
and generate ozone (ironic for an air purifier!).
Clearly the motor has a built-in controller - the circuit board is visible.
So the main PCB will be talking to it somehow, either an analog control voltage, PWM, serial or
some more proprietry method. The motor may also be talking back reporting actual speed and
possibly current (ie for detecting seized bearings etc).
So the other 4 wires in the 6 wire connector need investigation - multimeter will identify
analog / PWM signal, but a 'scope or logic-analyzer might be needed for serial/other.
