bunnings 4w bathroom fans

Thats low power. I want to force ventillate my roof cavity next summer, a
couple of these could be the go.

Ad material - mentions magnetic "air" bearings, efficient blade design but
not a lot more.

 http://www.arlec.com.au/wtyFiles/MEF25/MEF25_A4Flyer_V2.pdf

Id be interested to see just how it works. I think the clue is in the
oscillations prior to normal rotation. I have a friend who is an expert
on electric motors though the ones he works on consume kilowatts of
power. I will see if he has any ideas on these. For $19 I must just go
to Bunnings and buy one. I have a couple of places here where they could
be useful. Wonder if the motor is encased?

"syd bluemountains"




** Most likely it is a low voltage brushless DC motor, as used in countless
equipment fans these days, driven from an inbuilt 240V inverter from the AC
supply.

The 4 watts input figure is mighty low for the 100 litre per second flow
being claimed -  I suspect convection might be helping ....

The bit about magnetic air bearings is a furphy - BLDC motors can all claim
the same.


...  Phil

From the ad-blurb:

"Unique motor design utilises permanent magnets to act as air bearings thus
reducing wear on shaft"

You're probably right there Phil, if they worked I would have thought the
benefit to promote would have been lower friction rather than lower wear on
the shaft.

"Dennis"

http://www.greentopia.com.au/Energy-Efficient-25cm-Exhaust-Fan-Arlec/MEF25.htm



** The magnets in a BLDC motor tend to centre the rotor so there is no " end
thrust"  -  important if the motor shaft is operating in the vertical plane
as it is with a ceiling fan.

IME however, the most common failure with plain bearing fans is due to
drying out of the lubrication used -  mini size fans make horrible noises
and run slow while larger room fans simply seize up tight until one
relubricates the shaft.

BTW:

WES Components have a range of ceramic bearing fans with enormous rated life
spans and very affordable prices.


....  Phil

http://www.greentopia.com.au/Energy-Efficient-25cm-Exhaust-Fan-Arlec/MEF25.htm



Yep, same experience, combination of lint build up & dry bearings. A clean &
relube and its good for another year or so.

Mine is mounted on the wall vertically to replace a wall bathroom fan.

Seems to work well after the initial 1 second jitter.

It does have a sound to it, like a higher frequency than a normal fan
but could be
my imagination.

If it is a dc brushless fan with 240v inverter it would be good to
hack one to
run off DC via a solar panel.

Yes - especially as I want to buy a couple for getting 70C hot air out of my
roof space in summer. I already have a couple of 4 or 5W panels.......

Every bathroom fan we've ever had has had to deal with a buildup of crud,
sometimes it's that that eventually causes its downfall. With such a low
torque, you'd either be regularly having to take it down and clean it, or
else if it doesn't tolerate stall well it might not last too long.

Since we've tiled every room in the house airborne lint seems to kill
ceiling fans in <2yrs.