Electronics > Mechanical & Automation Engineering

What sort of brushless motor to make an extractor fan?

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I'm looking to replace a conventional single speed mains powered extractor fan for a bathroom with something that can be speed controlled via a low voltage ESC and micro. The operating voltage has to be under 48v due to the onerous wiring regulations in my country. Looking at the specs of new fans it looks like I'll need approximately 10-20 watts of power.

Would looking at the motors used in quadcopters and RC planes be a good place to start?
There is a bewildering array of options and I have no idea how to even begin to figure out what sort of motor would be a suitable drop in replacement. I'm guessing that I would need to use a sensored model to avoid cogging, and therefore noise, at low rpms.

David Hess:
Given your requirements I would consider using one or more standard 12 volt 4-wire PWM 120mm computer fans.

I'm not sure how long a computer fan would withstand the moist environment of a bathroom.

Computer case fans usually are not optimized for high static pressure which is needed to push the air thru a pipe. So unless there is no pipe or a very short pipe, it probably won't work well. CPU fans which are more likely to be optimized for higher static pressure may work better.

That apart, sensorless BLDC drive is a good candidate for a fan application, as it starts under no-load conditions.
However, a minimum RPM is necessary for the back EMF for the controller.
RC boat motor and controller is a possibility, but they probably run too fast.


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