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

[Sylvia Else]

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.

 

[Rheilly Phoull]

On 26/12/2017 2:54 PM, Sylvia Else wrote:

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.

Yeah, you would expect better quality having spent all that money on it.

 

[John Larkin]

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
<sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jim Thompson]

On Tue, 26 Dec 2017 10:21:55 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

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

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

It's what you learn, after you know it all, that counts.

 

[rickman]

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

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

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

 

[John S]

On 12/26/2017 12:21 PM, John Larkin wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

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.

 

[Phil Hobbs]

On 12/26/2017 03:31 PM, John S wrote:

On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.

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

http://electrooptical.net
https://hobbs-eo.com

 

[Computer Nerd Kev]

In aus.electronics John S <Sophi.2@invalid.org> wrote:

On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

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.

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.

--
__ __
#_ < |\| |< _#

 

[John S]

On 12/26/2017 2:44 PM, Phil Hobbs wrote:

On 12/26/2017 03:31 PM, John S wrote:
On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.


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

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]

 

[John S]

On 12/26/2017 2:44 PM, Phil Hobbs wrote:

On 12/26/2017 03:31 PM, John S wrote:
On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.


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

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

 

[Sylvia Else]

On 27/12/2017 5:21 AM, John Larkin wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

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.

 

[rickman]

John S wrote on 12/26/2017 3:31 PM:

On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.

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

 

[David Eather]

On Wed, 27 Dec 2017 06:31:28 +1000, John S <Sophi.2@invalid.org> wrote:

On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.
Wouldn't those two things cancel?


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.

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.

--
The latest set of Shadow Broker tools shows the UK, USA, Canada,
Australian and New Zealand spy agencies were hacking into domestic home
routers. Who gave them permission to spy on our kids?

 

[John Larkin]

On Tue, 26 Dec 2017 15:44:21 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/26/2017 03:31 PM, John S wrote:
On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.


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

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

 

[Sylvia Else]

On 27/12/2017 12:26 PM, John Larkin wrote:

On Tue, 26 Dec 2017 15:44:21 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/26/2017 03:31 PM, John S wrote:
On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.


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

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.

One option whether it's a PSC motor or a shaded pole motor is to reverse
the stator, and deal with any wire routing issues that arise. However,
in the case of the motor I had, it's been designed to make reversing it
impossible - perhaps so that the people used to assemble it can't get it
wrong.

Mind you, I'd have thought connecting the multiple stator wires to their
leads would be the biggest source of error.

Sylvia.

 

[Sylvia Else]

On 26/12/2017 5:54 PM, Sylvia Else wrote:

I decided I was unwilling to be defeated, and a fair amount of
soldering, heatshrinking and hot gluing later, I got it to work.

https://www.youtube.com/watch?v=GWB9I33k-Rs

Sylvia.

 

[FMurtz]

John S wrote:

On 12/26/2017 12:21 PM, John Larkin wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?


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.

If you reversed the motor, you would also reverse the blades because
although the blades would pass air either way ,they work more efficiently

 

[Steve Wilson]

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

Many turbine propeller aircraft can reduce their landing roll by placing the
propellers in reverse pitch. The blades are still turning in the same
direction, but the thrust vector is reversed. They are not very efficient in
this mode, but are still able to slow the aircraft.

To visualize what would happen in a pedestal fan, imagine turning it around
180 degrees. The motor is still spinning the propeller in the same direction,
but the thrust vector is reversed in relation to the floor.

In order to reverse the thrust vector, either the propeller pitch has to be
reversed, or the motor has to be reversed.

John is right. Doing both would cancel.

 

[FMurtz]

Steve Wilson wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

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.

Wouldn't those two things cancel?

Many turbine propeller aircraft can reduce their landing roll by placing the
propellers in reverse pitch. The blades are still turning in the same
direction, but the thrust vector is reversed. They are not very efficient in
this mode, but are still able to slow the aircraft.

To visualize what would happen in a pedestal fan, imagine turning it around
180 degrees. The motor is still spinning the propeller in the same direction,
but the thrust vector is reversed in relation to the floor.

In order to reverse the thrust vector, either the propeller pitch has to be
reversed, or the motor has to be reversed.

John is right. Doing both would cancel.

Wrong,reversing motor would reverse air flow, reversing the propeller
would be same air direction but would put the leading edge in the right
position for efficiency.

 

[Sylvia Else]

On 27/12/2017 3:02 PM, Sylvia Else wrote:

On 26/12/2017 5:54 PM, Sylvia Else wrote:

I decided I was unwilling to be defeated, and a fair amount of
soldering, heatshrinking and hot gluing later, I got it to work.

https://www.youtube.com/watch?v=GWB9I33k-Rs

Sylvia.

One issue I haven't addressed is that the fan is held on by a left-hand
threaded nut, because a right-hand threaded nut will tend to undo itself
in this application. Since I've reverse the direction, I really need the
nut to be right-hand threaded, but there's no way I can change the
threadedness of the shaft.

May need to use some more hot glue - we'll see.

Sylvia.