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Fun with Brushless DC motors, BLDCs.

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    Fun with Brushless DC motors, BLDCs.

    Hi Everyone,

    Last night I took apart a remote controlled (434MHz FSK) DC ceiling fan I'm planning to install in my home.

    I wanted to see if there was a way to attach a Z-Wave control module to integrate the fan with HomeSeer. I currently use a Bond Home by Olibra to achieve this with two other installs of the same model fan, but there's a lot of room for improvement (latency, status).

    During this disassembly I got to learn about brushless DC motors. Why they are different from traditional brushed DC motors, the theory of the three phase motor, need for an electronic speed controller and hall effect sensors.

    Once I had my head wrapped around this, it became clear the DC motor controllers such as the Qubino would not be suitable, as these are not designed for three phase motors.

    So that brought me back to the Qubino 0-10v dimmer, it's intended for lights but I know 0-10v is often used for motor speed control. The setup would be something like:

    Z-Wave controller > Qubino 0-10v > 0-10v signal interpreted by ESC > Control of BLDC.

    I know some ESCs work with PWM instead of 0-10v. I've successfully controlled a PWM LED driver by passing the 0-10v from a Qubino through a PWM converter. So that's also an option.

    I'm wondering if anyone has any experience in the general area of BLDCs and could you share your experiences and successes? Or at least some experience with electronic speed controllers? What brand and voltage did you buy, what purpose did you use them for? Did you use a 0-10v controller (not necessarily z-wave) to adjust them?

    My final question is about the feedback loop from the fan motor. From time spent on YouTube university I now understand the rough idea of Hall effect sensors to determine the position of the rotor. But everything I watched indicated this would require at least three wires for the return signal.

    The fan controller I'm working with has only two wires providing feedback from the motor. Can anyone name or suggest what this feedback method might be? It will be important if I decide to replace the ESC entirely.

    A closer looks shows the control path looks like:

    RF receiver (434MHz) a daughter board with a two-pin serial connection to a microcontroller --> Microcontroller (ST7MC1K2) --> A MOSFET chip that pulls 15V high or low on each of the three BLDC phases based on the motor control output of the ST7MC1.

    The two wire input I now believe is a tachometer, used for motor control at low speeds. When the motor speed is >50%, it switches to Back EMF sensing for sensor-less motor control. So no Hall sensors required.

    I'm currently trying to understand the ST7MC1 microcontroller. If exterior analogue control is going to be applied anywhere, it will be on one of the pins of this chip. It's a 32 pin chip with 8 pins to a side. The documentation provided by ST microelectronics is extensive at >300pages, but I'm honestly struggling to understand most of it. It's further complicated by the fact the chip is not just a motor controller, it has several other functions in the one package.