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OT: Running a pedestal fan in reverse - failed - a rant of sorts.

For reasons I need not go into, I wanted to make a cheap pedestal fan blow backwards, by putting the fan on backwards, and running the motor in reverse.

The motor is a typical PSC motor, and reversing it should be just a matter of switching a pair of connections to put the capacitor into the other phase.

It took me a while to figure out which two wires to swap, but I'm confident I identified the correct two. Didn't work. After I'd reassembled it the motor didn't run at all, nor make any sound. I may have blown the thermal fuse while curing some heat shrink.

Not the failure surprised me - working on this motor is like doing brain surgery. The stator windings aren't terminated with insulated wire attached to the stator, but are just loose copper wires that are soldered to insulated wires, with the junctions covered with glass fiber tube, which are then bunched together and then attached to the stator with a couple of cable ties. While working on it, any careless movement can break a wire (and break one I did, but was able to solder it back).

How on Earth do they make these with any kind of reliability? Or is the labour so cheap that they're happy to throw away any that don't work after assembly.

The electrical separation of the two stator windings also depends on the enamel, and nothing else.

I question its claim to be double insulated - OK, the instructions do say not to run it unless it's fully assembled, but the typical punter wouldn't realise that the only thing preventing the metal shaft becoming live is the copper wire enamel.

Anyway, dead waste of $15.

Sylvia.

Reply to
Sylvia Else
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Yeah, you would expect better quality having spent all that money on it.

Reply to
Rheilly Phoull

Out of respect, I'm not going to ask why you didn't simply turn the pedestal fan around 180-degrees. :)

Reply to
mpm

the small mains fan motors I've played with have generally been shaded pole.

they don't

Spend twice that on a 1950s fan and it'll probably serve you for life.

NT

Reply to
tabbypurr

Wouldn't those two things cancel?

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

{>8-} "putting the fan on backwards" ?>:-] ...Jim Thompson

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Reply to
Jim Thompson

John Larkin wrote on 12/26/2017 1:21 PM:

Turning the blads on backwards only makes them work less efficiently. Turning the motor backwards makes the air blow the other way, but also works the blades less efficiently. Doing both makes the air blow the other way, but also allows the blades to work with the proper leading edge and so more efficiently.

--

Rick C 

Viewed the eclipse at Wintercrest Farms, 
on the centerline of totality since 1998
Reply to
rickman

It seems to me that they would. Reversing the motor makes it blow in the opposite direction. Reversing the blades makes it blow in the opposite direction.

Reply to
John S

You'd need to mirror-image the blades to make them blow the other way without reversing the motor, ISTM. Just turning them round wouldn't do it.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

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Reply to
Phil Hobbs

I'm useless at this sort of thing, so I figured I'd get some practice working it out:

A working solution to having a fan blow the other way is to turn it around. The effect of this relative to an observer in a fixed position is that the blades are rotated and the direction of spin is reversed. So to have the fan blow the other way without rotating it requires that the blades be rotated and spun in the opposite direction.

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Reply to
Computer Nerd Kev

From Wikipedia:

Propeller-driven aircraft generate reverse thrust by changing the angle of their controllable-pitch propellers so that the propellers direct their thrust forward. This reverse thrust feature became available with the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Single-engine aircraft tend not to have reverse thrust. However, single-engine turboprop aircraft such as the PAC P-750 XSTOL,[6] Cessna 208 Caravan, and Pilatus PC-6 Porter do have this feature available.[citation needed]

Reply to
John S

I studied the situation a bit more. You are correct, Phil.

Reply to
John S

No.

Imagine you have a piece of right-hand threaded rod. Whichever end you look at it from, it's still right-hand threaded.

Sylvia.

Reply to
Sylvia Else

Yes, because you realise that I've obviously thought of that, and have a reason why it's not sufficient.

Sylvia.

Reply to
Sylvia Else

Yes, the small ones tend to be. None of the 40W pedestal fan motors I've had occasion to disassemble over the years (usually because they're seizing up) have been shaded-pole. Presumably there's some economic driver to this, but I don't know what it might be.

Sylvia.

Reply to
Sylvia Else

Reversing the blade does *not* make the fan blow in the opposite direction. Look at a fan blade and you will see this immediately.

--

Rick C 

Viewed the eclipse at Wintercrest Farms, 
on the centerline of totality since 1998
Reply to
rickman

Turning the blade around just changes the relative position of what you would normally call the leading edge. If the fan still runs in the same direction it will still blow in the same direction but the once was leading edge is now the trailing edge. Sylvia has the process right. Trust an ex-aircraft model flyer on it.

--
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Reply to
David Eather

I guess it's like screw threads, same sense from either end. If it's a shaded-pole motor, the only thing to do is heat-gun the blades.

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Oh well, that's an easy one to answer: GREED! :)

Reply to
mpm

No. The fan blades are a right-hand screw whether pointed forward or backward. You'd have to scan 'em and invert the Z coordinate axis and 3D print a new set, or reach into a mirror and pull out the image.

Reply to
whit3rd

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