Motor control for single phase capacitor start fan motor

[Wade BeattyParticipant @wadebeatty78296]

Good afternoon, I just picked up a nice and free squirrel cage fan that ai will use for extraction near my surface grinder. This isn’t for sparks but for fine dust that settles near the machine. I am building a wall to further protect my other machines.

What is the best way to install a speed control on this motor?

Thanks, Wade

[John HaineParticipant @johnhaine32865]

https://www.bes.co.uk/fan-speed-controller-27219/

[Robert Atkinson 2Participant @robertatkinson2]

A single phase inducion motor like this is actually quite hard to control. The simple controllers like the one linked to by John do work but have some limitation. Effectively they adjust the power availble to the motor so the “slip” between the syncronous speed determined by the supply frequency and tha actual speed increases. This is OK for a constant load like a ceiling fan but if there is a variable load or a blockage you may have issues.
you can get VFDs for single phase motoer which are better but even more expensive.

Robert.

[David JuppParticipant @davidjupp51506]

May sound like a daft question, but is speed control actually needed?

Many centrifugal fans or pumps are controlled by throttling the outlet line.  The consumed power varies roughly with the mass flow of fluid, though there is obviously a minimum at zero flow.

[MacolmParticipant @macolm]

An exception to the difficulty of controlling a single phase induction motor is when it is driving a fan. This is because the drag decreases quits rapidly as the speed falls, more quickly indeed than the available torque as the motor voltage is reduced. It is thus stable over a reasonable range of speeds.

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