Thread: Bathroom exhaust fan problem

I doubt it's the frequency of the mains. It's probably a shaded pole asynchronous motor, commonly used in fans. They should only ever rotate in one direction.

I don't know why it would change.

I pulled our toilet exhaust fan down recently to disassemble it and lubricate the bearings as it was running slower and noisy.

See also Shaded Pole Induction Motor Working and Application Explained - ETechnoG

I think these fans depend on the frequency of the 240 50Hz power as they rattle around on start up and I wonder if the frequency is going off 50Hz , as it usually happens early in the morning. Usually a restart will fix it (after you find the bathroom is fogged up on exiting the shower)

Sorry mate, it is absolutely impossible for the frequency to be the problem. The complete grid is locked to the same frequency, be it 50 Hz or 60Hz. A very small "drift" MAY be possible, in the order of 0.1 or so and will be adjusted over a period of a day or so that 50 Hz is the net result over 24 hours.
Otherwise there would be all sorts of problems with frequency dependent equipment, such as clocks.

Some of those small fans have very little starting torque, and can be affected by a natural air flow such as a small breeze, causing them to turn backwards when turned off. Also indicated by the rattling around that you can hear.

Also indicated by the rattling around that you can hear.

The rattling is a characteristic of the motor type and warned about in the manual and on tags on the fan.

It is not a conventional motor like in the previous post. It is brushless and does not have magnets except around the shaft. It only draws about AFAIR 6watts or so, not the 36waatts of a conventional motor.
Regards PhilipA

One word, "arlec". I would refuse to install anything arlec for any of my customers, always had trouble one way or another.
I did used to install a lot of airflow fans, never an issue.

Originally Posted by PhilipA

The rattling is a characteristic of the motor type and warned about in the manual and on tags on the fan.

It is not a conventional motor like in the previous post. It is brushless and does not have magnets except around the shaft. It only draws about AFAIR 6watts or so, not the 36waatts of a conventional motor.
Regards PhilipA

Ok, in which case it is a permanent magnet motor. Shaded pole motors also do not have brushes. Rattling or growling is then probably a magnetic noise, similar to a split phase motor with a faulty start winding. Cheers

If it is rattling then it could also be weak plastic mountings wings. You did mention Arlec & Made in China in the same breath.

An existing back draft would be my guess for it reversing on start as mentioned by OF, but it would need to be sort of substantial but who knows????.

Airflow is my choice of exhaust fan as well.

The rattling is a characteristic of the motor type and warned about in the manual and on tags on the fan.

That should have been a warning as no reputable Australian Manufacturer would release a product onto the market knowing full well there is an existing problem like that. Fancy

Just have cold showers, Philip.

Just have cold showers, Philip.

Before, after or instead of, the choice is yours.