3-speed fan motor

[[email protected]]

I notice that a lot of fans, including all I have recently bought, have
3 speeds controlled by a switch. So I was wondering how they manage to
control the speed (yeah, I know ... via the position of the switch
Latest one I bought has parts more visible (I don't want to take them
apart). There are 4 wires to the switch. So it would seem likely that
one wire is common and the other 3 are selected by position, and none
are selected for off. There's a 3uf capacitor and what looks like a
shaded-pole winding in the motor itself.

The motor type that seems to fit is "permanent split-capacitor", also
known as "capacitor start and run".

If the starting winding is permanently connected, is there any design
change over that of a switched winding that is needed because it will
be permanently powered? For example would the number of winding turns
need to be greater? Or maybe different capacitor? Or at at different
angle in the stator?

I read that the switch selects taps in the main winding for speed. But
is this just a selection that affects slip, or does it change the way
the winding is slectrically configured? Could more taps allow more steps
in motor speed? Is there a low end limit on the speed that can be set
this way?

I have noticed that it always is the case that the first position next
to the off position is the highest speed position. Is this done because
that is the best for starting the fan from a not-running state?

I tested a couple of fans I have (the circulate air in the computer room
by getting them spinning in the wrong direct by driving the backware with
another face facing into it. Then I flip the switch and notice that the
fan has no trouble getting started by quickly slowing down the rotation
that's going in the wrong direction, to a stop, then going in the right
direction. This works fine even which quickly switched to the slow speed.

My father has a ceiling fan with a pull chain that increments the speed
in steps with 3 speeds possible, and also has a wall switch with 3 speeds.
Turns out there there are more than just 3 speeds possible based on the
combinations of both switches. How does this happen? I have not looked
at the wiring, but I assume there are as many wires as the wall switch
needs to have going between the fan and the wall switch. Could the pull
chain switch be selecting different taps on the other end of the winding?

The ceiling fan has a reverse switch. I'm guessing that simply reverses
the permanent start winding.

 

[JohnR66]

I notice that a lot of fans, including all I have recently bought, have
3 speeds controlled by a switch. So I was wondering how they manage to
control the speed (yeah, I know ... via the position of the switch
Latest one I bought has parts more visible (I don't want to take them
apart). There are 4 wires to the switch. So it would seem likely that
one wire is common and the other 3 are selected by position, and none
are selected for off. There's a 3uf capacitor and what looks like a
shaded-pole winding in the motor itself.

The motor type that seems to fit is "permanent split-capacitor", also
known as "capacitor start and run".

Yes, these seem to be PSC. With the cap removed, they will not start. If
already runing and the cap removed, the will continue runing, but current
draw will increase. They are less efficient in this mode.

If the starting winding is permanently connected, is there any design
change over that of a switched winding that is needed because it will
be permanently powered? For example would the number of winding turns
need to be greater? Or maybe different capacitor? Or at at different
angle in the stator?

I guess it is a matter of economics. Sizing the cap for each speed position
might maximize efficiency, extra capacitors and more complex switch.

I read that the switch selects taps in the main winding for speed. But
is this just a selection that affects slip, or does it change the way
the winding is slectrically configured? Could more taps allow more steps
in motor speed? Is there a low end limit on the speed that can be set
this way?

Lower speed switches in more windings which means lower current thus less
torque.

I have noticed that it always is the case that the first position next
to the off position is the highest speed position. Is this done because
that is the best for starting the fan from a not-running state?

I always thought this as well, but not positive.

I tested a couple of fans I have (the circulate air in the computer room
by getting them spinning in the wrong direct by driving the backware with
another face facing into it. Then I flip the switch and notice that the
fan has no trouble getting started by quickly slowing down the rotation
that's going in the wrong direction, to a stop, then going in the right
direction. This works fine even which quickly switched to the slow speed.

I noticed that some PSC motors will run backwards if power is applied while
the shaft has been rotated at nearly full running speed backwards.

My father has a ceiling fan with a pull chain that increments the speed
in steps with 3 speeds possible, and also has a wall switch with 3 speeds.
Turns out there there are more than just 3 speeds possible based on the
combinations of both switches. How does this happen? I have not looked
at the wiring, but I assume there are as many wires as the wall switch
needs to have going between the fan and the wall switch. Could the pull
chain switch be selecting different taps on the other end of the winding?

Not sure.

The ceiling fan has a reverse switch. I'm guessing that simply reverses
the permanent start winding.

Not sure, but it would seem logical that this is what is being done.
John

 

[[email protected]]

|
|> I read that the switch selects taps in the main winding for speed. But
|> is this just a selection that affects slip, or does it change the way
|> the winding is slectrically configured? Could more taps allow more steps
|> in motor speed? Is there a low end limit on the speed that can be set
|> this way?
|
| Lower speed switches in more windings which means lower current thus less
| torque.

So that lower torque plus the drag on the blades results in the lower
speed. If operated in a vacuum, the speeds might be a lot closer with
only the mechanical drag?

I notice the full speed on most of these fans seems to be about 1 rps
different than the power frequency, or some multiple thereof. The
observation is that there is a slight change in the timbre of the sound
emitted by the motor that cycles around 1 per second, but can vary a
lot, including with variation in air flow around the fan. That's at
full speed setting. At lower speeds the sound is more like a flutter
and does not seem to change as much.

Some day I might take one of these fans apart and substitute a sync
motor and see what happens


|> I tested a couple of fans I have (the circulate air in the computer room
|> by getting them spinning in the wrong direct by driving the backware with
|> another face facing into it. Then I flip the switch and notice that the
|> fan has no trouble getting started by quickly slowing down the rotation
|> that's going in the wrong direction, to a stop, then going in the right
|> direction. This works fine even which quickly switched to the slow speed.
|
| I noticed that some PSC motors will run backwards if power is applied while
| the shaft has been rotated at nearly full running speed backwards.

I used to have an electric clock that would go backwards about half the
times it would be plugged in. I would guess the shade winding has been
broken or the cap disconnected/loose.

It was a fun clock to have.

 

[J. B. Wood]

|> I tested a couple of fans I have (the circulate air in the computer room
|> by getting them spinning in the wrong direct by driving the backware with
|> another face facing into it. Then I flip the switch and notice that the
|> fan has no trouble getting started by quickly slowing down the rotation
|> that's going in the wrong direction, to a stop, then going in the right
|> direction. This works fine even which quickly switched to the slow speed.
|
| I noticed that some PSC motors will run backwards if power is applied while
| the shaft has been rotated at nearly full running speed backwards.

I used to have an electric clock that would go backwards about half the
times it would be plugged in. I would guess the shade winding has been
broken or the cap disconnected/loose.

It was a fun clock to have.

Hello, and years ago many of the better quality box-type fans were
intended to be used on the floor or in a window. For window fan use they
had an "in/out" switch that would reverse the direction of blade
rotation. Most of these fans had a special type shaded-pole motor with
two sets of externally-connected shaded windings. Other than that the
motor construction was conventional. With the shaded pole windings
open-circuited you could cause the motor to rotate in either direction by
manually spinning the fan blades in that direction. Although the motor
would continue to run in this mode it produced minimal torque compared to
having one of the shaded-pole windings in the circuit. Sincerely,

John Wood (Code 5550) e-mail: [email protected]
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

 

[[email protected]]

|
|> |> I tested a couple of fans I have (the circulate air in the computer room
|> |> by getting them spinning in the wrong direct by driving the backware with
|> |> another face facing into it. Then I flip the switch and notice that the
|> |> fan has no trouble getting started by quickly slowing down the rotation
|> |> that's going in the wrong direction, to a stop, then going in the right
|> |> direction. This works fine even which quickly switched to the slow speed.
|> |
|> | I noticed that some PSC motors will run backwards if power is applied while
|> | the shaft has been rotated at nearly full running speed backwards.
|>
|> I used to have an electric clock that would go backwards about half the
|> times it would be plugged in. I would guess the shade winding has been
|> broken or the cap disconnected/loose.
|>
|> It was a fun clock to have.
|
| Hello, and years ago many of the better quality box-type fans were
| intended to be used on the floor or in a window. For window fan use they
| had an "in/out" switch that would reverse the direction of blade
| rotation. Most of these fans had a special type shaded-pole motor with
| two sets of externally-connected shaded windings. Other than that the
| motor construction was conventional. With the shaded pole windings
| open-circuited you could cause the motor to rotate in either direction by
| manually spinning the fan blades in that direction. Although the motor
| would continue to run in this mode it produced minimal torque compared to
| having one of the shaded-pole windings in the circuit. Sincerely,

I'm also curious why it seems to common that the first speed right after
the off position is the highest speed. Could it be that this speed was
necessary to counter the fact that the blade may be rotating in the wrong
direction due to airflow through the window or such? I have tried all
the fans I have ever owned by putting them in the lowest speed position
while unplugged, the plugging them in to start. They always start OK,
unless the fan is generally dead (after many years of service a couple
of them have pretty much frozen up with all kinds of dust and gunk in the
motor, which I should have cleaned out, but didn't). So it seems the
first position being high isn't to start the fan from a stop, but maybe
it needs it to start from reverse rotation.

Also, it seems to me if a motor of this type is going to have 4 wires to
the winding, it could achieve 4 speeds instead of just 3 speeds, with the
taps being in different positions. Two of the wires would be on one end
of the winding, and the other two on the other end. I'll label them as
A, B, C, D. It could look like:

A---B-----C------D

Connect to B and C for high speed.
Connect to A and C for medium high speed.
Connect to B and D for medium low speed.
Connect to A and D for low speed.

It would be no more cost on the motor than redesigning for different tap
positions on the winding. The switch would cost a bit more to have the
extra position. But maybe it's not worth it in the market.

Long long ago my grandfather had a fan that had a smooth speed adjustment.
This was around early 1960's. I have no idea how they did that. I do not
recall there being a zillion wires from the knob to the motor.

 

[Bud--]

|
|> |> I tested a couple of fans I have (the circulate air in the computer room
|> |> by getting them spinning in the wrong direct by driving the backware with
|> |> another face facing into it. Then I flip the switch and notice that the
|> |> fan has no trouble getting started by quickly slowing down the rotation
|> |> that's going in the wrong direction, to a stop, then going in the right
|> |> direction. This works fine even which quickly switched to the slow speed.
|> |
|> | I noticed that some PSC motors will run backwards if power is applied while
|> | the shaft has been rotated at nearly full running speed backwards.
|>
|> I used to have an electric clock that would go backwards about half the
|> times it would be plugged in. I would guess the shade winding has been
|> broken or the cap disconnected/loose.
|>
|> It was a fun clock to have.
|
| Hello, and years ago many of the better quality box-type fans were
| intended to be used on the floor or in a window. For window fan use they
| had an "in/out" switch that would reverse the direction of blade
| rotation. Most of these fans had a special type shaded-pole motor with
| two sets of externally-connected shaded windings. Other than that the
| motor construction was conventional. With the shaded pole windings
| open-circuited you could cause the motor to rotate in either direction by
| manually spinning the fan blades in that direction. Although the motor
| would continue to run in this mode it produced minimal torque compared to
| having one of the shaded-pole windings in the circuit. Sincerely,

I'm also curious why it seems to common that the first speed right after
the off position is the highest speed. Could it be that this speed was
necessary to counter the fact that the blade may be rotating in the wrong
direction due to airflow through the window or such? I have tried all
the fans I have ever owned by putting them in the lowest speed position
while unplugged, the plugging them in to start. They always start OK,
unless the fan is generally dead (after many years of service a couple
of them have pretty much frozen up with all kinds of dust and gunk in the
motor, which I should have cleaned out, but didn't). So it seems the
first position being high isn't to start the fan from a stop, but maybe
it needs it to start from reverse rotation.

Could be to give a reasonable speed acceleration. And to give a high
enough torque to start against all kinds of dust and gunk. (I had a
gunked up fan that would start on high, but not the other speeds.)

 

[[email protected]]

| [email protected] wrote:
|>
|> Also, it seems to me if a motor of this type is going to have 4 wires to
|> the winding, it could achieve 4 speeds instead of just 3 speeds, with the
|> taps being in different positions. Two of the wires would be on one end
|> of the winding, and the other two on the other end. I'll label them as
|> A, B, C, D. It could look like:
|>
|> A---B-----C------D
|>
|> Connect to B and C for high speed.
|> Connect to A and C for medium high speed.
|> Connect to B and D for medium low speed.
|> Connect to A and D for low speed.
|
|
| The taps are not designed to work that way.

Then how are they designed to work?


|> It would be no more cost on the motor than redesigning for different tap
|> positions on the winding. The switch would cost a bit more to have the
|> extra position. But maybe it's not worth it in the market.
|>
|> Long long ago my grandfather had a fan that had a smooth speed adjustment.
|> This was around early 1960's. I have no idea how they did that. I do not
|> recall there being a zillion wires from the knob to the motor.
|
|
| Its VERY simple. It used a variable inductor in series with the
| motor, rather than one with fixed taps.

It was a rather small one, then.

 

[[email protected]]

| Could be to give a reasonable speed acceleration. And to give a high
| enough torque to start against all kinds of dust and gunk. (I had a
| gunked up fan that would start on high, but not the other speeds.)

Today I found a 3-speed fan that has LO as the first speed and HI as the
last speed. There went the trend I had seen for decades. I bought it
($13) to see if it would work (Chinese made in Wal-Mart). It actually
did work. No idea how long that will last, though.