Hello,
I am new to this group and hope I am posting in the right category. I’m a home owner and all too often, involved in DIY projects that are way over my pay grade. So here goes: I have installed a ceiling fan with a 40 watt dc brush-less motor. At the fan’s junction box, there is a controller/transformer/receiver which receives the remote’s radio signal for speed adjustment and rotation direction. The fan is working well but I find the lower speed setting to still be to fast. The instructions specifically say not to install a wall dimmer or other voltage reducing device. After some reading, I found that this type of brush-less dc motor has three phase wires identified as V, U and W (they are actually also color coded red, pink and grey). I came across a general explanation of how this type of motor could be slowed down by adding resistors directly to these wires but my question is how and what type of resistors value should I use. Thank you for you patience in reading this post.
bdlem
Firstly, welcome to the community! It’s perfectly fine to seek advice on complex DIY projects; that’s what community and shared knowledge are all about. However, I must preface this by saying that modifying electrical components like a ceiling fan comes with safety risks. Therefore, it’s important to understand the implications and have some level of electrical competency.
Disclaimer
Tampering with the motor control circuitry could void the warranty, reduce the lifespan of the motor, or even create unsafe conditions. Therefore, proceed with caution and consult with professionals before making any modifications.
Basics of BLDC Motor Speed Control
The motor in your ceiling fan is a Brushless DC (BLDC) motor, and the speed of a BLDC motor is generally controlled by varying the voltage and frequency via the electronic controller. You mentioned that there are three phase wires identified as V, U, and W. These correspond to the three phases of the motor, which are energized in sequence to rotate the motor.
Why Resistors Aren’t Ideal
In some applications, resistors are added in series with a motor’s windings to reduce speed. However, this is generally not an ideal method for speed control because it reduces efficiency, can cause heat build-up, and isn’t very precise. In addition, resistors placed on the U, V, and W lines would impact the electronic commutation of the BLDC motor, which could lead to unpredictable behavior or even motor damage.