Hi all,

I've been given one of those big chrome floor standing 3 speed fans to
look at because it doesn't run. It was given to my mate (not running)
so I don't have any information beyond that.

When you power it up you can hear/ feel the thing 'humming' slightly,
suggesting it is receiving power yet the fan doesn't spin on any of
the speeds, even when the fan blade is given a little push (either
way). The fan blades are very free to move and the fan looks pretty
new (so I'm not ruling out a d.o.a.).

I think it's wired up like this:

http://waterheatertimer.org/images/M...citor1-800.jpg

(except it's not a 'start' cap / winding but 'run' on these motors
isn't it)?

Measuring ohms from neutral (basically across the L/N on the mains
plug) I get:

219 Ohms on speed 3, 375 on speed 2, 393 on speed 1 (slowest) and
infinity with it off (of course). ;-)

Measuring between the 3 wires coming out of the motor to the switch I
get: N-S3 = 219, S3-S2 = 157 and S2-S1 = 46 ohms (so doesn't quite
add up correctly (422 v 393)?

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

I can't see any thermal trips so apart from the cap breaking down
under load (I have one on order just in case) or it being wired up
incorrectly (within the motor, can't get at much in there without
cutting it open) I can't see what the cause of it not running is?

Any thoughts or ideas please?

Cheers, T i m

On Saturday, 24 June 2017 17:09:57 UTC+1, T i m wrote:
Hi all,

I've been given one of those big chrome floor standing 3 speed fans to
look at because it doesn't run. It was given to my mate (not running)
so I don't have any information beyond that.

When you power it up you can hear/ feel the thing 'humming' slightly,
suggesting it is receiving power yet the fan doesn't spin on any of
the speeds, even when the fan blade is given a little push (either
way). The fan blades are very free to move and the fan looks pretty
new (so I'm not ruling out a d.o.a.).

I think it's wired up like this:

http://waterheatertimer.org/images/M...citor1-800.jpg

(except it's not a 'start' cap / winding but 'run' on these motors
isn't it)?

Measuring ohms from neutral (basically across the L/N on the mains
plug) I get:

219 Ohms on speed 3, 375 on speed 2, 393 on speed 1 (slowest) and
infinity with it off (of course). ;-)

Measuring between the 3 wires coming out of the motor to the switch I
get: N-S3 = 219, S3-S2 = 157 and S2-S1 = 46 ohms (so doesn't quite
add up correctly (422 v 393)?

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

I can't see any thermal trips so apart from the cap breaking down
under load (I have one on order just in case) or it being wired up
incorrectly (within the motor, can't get at much in there without
cutting it open) I can't see what the cause of it not running is?

Any thoughts or ideas please?

Cheers, T i m

Normally these things use a squirrel cage motor plus 2 series caps for speed reduction.


NT

On Sat, 24 Jun 2017 11:01:33 -0700 (PDT), wrote:

snip

Normally these things use a squirrel cage motor plus 2 series caps for speed reduction.


Very sure this is stock and deffo only one cap.

It's one of these (not Clarke particularly).

https://www.machinemart.co.uk/p/clar...hrome-floor-f/

Cheers, T i m

T i m wrote:

On Sat, 24 Jun 2017 11:01:33 -0700 (PDT), wrote:

snip

Normally these things use a squirrel cage motor plus 2 series caps for
speed reduction.


Very sure this is stock and deffo only one cap.

It's one of these (not Clarke particularly).

https://www.machinemart.co.uk/p/clar...hrome-floor-f/

Cheers, T i m

Assuming it doesn't have brushes, and your continuity tests included the
switch, about the only thing you haven't excluded is shorted turns.
And possibly capacitor breakdown at mains voltage, so it's worth trying
the new one.

--

Roger Hayter

On 24/06/2017 17:09, T i m wrote:
Hi all,

I've been given one of those big chrome floor standing 3 speed fans to
look at because it doesn't run. It was given to my mate (not running)
so I don't have any information beyond that.

When you power it up you can hear/ feel the thing 'humming' slightly,
suggesting it is receiving power yet the fan doesn't spin on any of
the speeds, even when the fan blade is given a little push (either
way). The fan blades are very free to move and the fan looks pretty
new (so I'm not ruling out a d.o.a.).

I think it's wired up like this:

http://waterheatertimer.org/images/M...citor1-800.jpg

(except it's not a 'start' cap / winding but 'run' on these motors
isn't it)?

Measuring ohms from neutral (basically across the L/N on the mains
plug) I get:

219 Ohms on speed 3, 375 on speed 2, 393 on speed 1 (slowest) and
infinity with it off (of course). ;-)

Measuring between the 3 wires coming out of the motor to the switch I
get: N-S3 = 219, S3-S2 = 157 and S2-S1 = 46 ohms (so doesn't quite
add up correctly (422 v 393)?

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

What's the voltage across the winding? Higher the better. If its
nominally (230 - 206) then it suggests the winding is a resistor
indicating a shorted turn somewhere. I'd like to see 100V or more.

I can't see any thermal trips so apart from the cap breaking down
under load (I have one on order just in case) or it being wired up
incorrectly (within the motor, can't get at much in there without
cutting it open) I can't see what the cause of it not running is?

Any thoughts or ideas please?

Cheers, T i m

T i m wrote:
Hi all,

I've been given one of those big chrome floor standing 3 speed fans to
look at because it doesn't run. It was given to my mate (not running)
so I don't have any information beyond that.

When you power it up you can hear/ feel the thing 'humming' slightly,
suggesting it is receiving power yet the fan doesn't spin on any of
the speeds, even when the fan blade is given a little push (either
way). The fan blades are very free to move and the fan looks pretty
new (so I'm not ruling out a d.o.a.).

I think it's wired up like this:

http://waterheatertimer.org/images/M...citor1-800.jpg

(except it's not a 'start' cap / winding but 'run' on these motors
isn't it)?

Measuring ohms from neutral (basically across the L/N on the mains
plug) I get:

219 Ohms on speed 3, 375 on speed 2, 393 on speed 1 (slowest) and
infinity with it off (of course). ;-)

Measuring between the 3 wires coming out of the motor to the switch I
get: N-S3 = 219, S3-S2 = 157 and S2-S1 = 46 ohms (so doesn't quite
add up correctly (422 v 393)?

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

I can't see any thermal trips so apart from the cap breaking down
under load (I have one on order just in case) or it being wired up
incorrectly (within the motor, can't get at much in there without
cutting it open) I can't see what the cause of it not running is?

Any thoughts or ideas please?

Cheers, T i m


These normally use a shaded pole motor. The rule of thumb for feed
current via a capacitor is 80mA per uF. So you should have a maximum
current below this. measure the current with a moving coli meter.IME if
after stripping the motor and soaking the sintered bushes in an
oil/parafin mix then reassembling, you are looking for a duff connection
somewhere as your resistance reading seem reasonable. Good luck.

On 24/06/2017 20:28, Capitol wrote:
T i m wrote:
Hi all,

I've been given one of those big chrome floor standing 3 speed fans to
look at because it doesn't run. It was given to my mate (not running)
so I don't have any information beyond that.

When you power it up you can hear/ feel the thing 'humming' slightly,
suggesting it is receiving power yet the fan doesn't spin on any of
the speeds, even when the fan blade is given a little push (either
way). The fan blades are very free to move and the fan looks pretty
new (so I'm not ruling out a d.o.a.).

I think it's wired up like this:

http://waterheatertimer.org/images/M...citor1-800.jpg

(except it's not a 'start' cap / winding but 'run' on these motors
isn't it)?

Measuring ohms from neutral (basically across the L/N on the mains
plug) I get:

219 Ohms on speed 3, 375 on speed 2, 393 on speed 1 (slowest) and
infinity with it off (of course). ;-)

Measuring between the 3 wires coming out of the motor to the switch I
get: N-S3 = 219, S3-S2 = 157 and S2-S1 = 46 ohms (so doesn't quite
add up correctly (422 v 393)?

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

I can't see any thermal trips so apart from the cap breaking down
under load (I have one on order just in case) or it being wired up
incorrectly (within the motor, can't get at much in there without
cutting it open) I can't see what the cause of it not running is?

Any thoughts or ideas please?

Cheers, T i m


These normally use a shaded pole motor. The rule of thumb for feed
current via a capacitor is 80mA per uF. So you should have a maximum
current below this. measure the current with a moving coli meter.IME if
after stripping the motor and soaking the sintered bushes in an
oil/parafin mix then reassembling, you are looking for a duff connection
somewhere as your resistance reading seem reasonable. Good luck.

The OP has already measured the capacitor value to be 2uF. With 206V on
speed '1' I would expect around 150mA and I guess would confirm that
side is working.

There aren't many AC moving coil ammeters still around! I think we're
talking clamp meter which is a lot less intrusive.

On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

and your continuity tests included the
switch,

They did, and without (just in case). I also forgot to mention there
was a sort circuit between neutral and one side of the run winding.

about the only thing you haven't excluded is shorted turns.

And I think that would be difficult without knowing the original
resistance of the windings.

And possibly capacitor breakdown at mains voltage, so it's worth trying
the new one.

Check. It should be here on Monday. ;-)

Cheers, T i m

On Saturday, 24 June 2017 21:05:13 UTC+1, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I don't think it can be. Sychronous motors lock to the mains frequency. Fan motors have slip.

and your continuity tests included the
switch,

They did, and without (just in case). I also forgot to mention there
was a sort circuit between neutral and one side of the run winding.

about the only thing you haven't excluded is shorted turns.

And I think that would be difficult without knowing the original
resistance of the windings.

And possibly capacitor breakdown at mains voltage, so it's worth trying
the new one.

Check. It should be here on Monday. ;-)

Cheers, T i m

someone needs a junkbox.


NT

On 24/06/2017 21:05, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I think I would call them shaded pole induction motor:

https://en.wikipedia.org/wiki/Shaded-pole_motor

But who knows the economics of motors and control gear these days.

On Sat, 24 Jun 2017 20:22:35 +0100, Fredxxx wrote:

snip

There is also a run (?) cap of 2uF that tests out on my DMM (as 2uF)
(and open circuit on the ohms test) and a run winding that measures
375 ohm. Measuring the voltage across the cap with it on speed 1 gives
206V (does that sound right)?

What's the voltage across the winding? Higher the better. If its
nominally (230 - 206) then it suggests the winding is a resistor
indicating a shorted turn somewhere. I'd like to see 100V or more.

Now that's weird ... I just put the meter on it again to read the
voltage across the run coil, powered it up and it started working!

However, it then slowed down again (below that of speed 1) so is it
looking more like a bad run cap (given that the thing looks new and
all the coils are a nice clean copper colour and seem to read
reasonably)?

Cheers, T i m

On Sat, 24 Jun 2017 13:09:20 -0700 (PDT), wrote:

On Saturday, 24 June 2017 21:05:13 UTC+1, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I don't think it can be. Sychronous motors lock to the mains frequency.

Ok.

Fan motors have slip.

Sure, I was probably just differentiating between a brushed and
non-brushed motor. ;-(

snip

Check. It should be here on Monday. ;-)


someone needs a junkbox.

'Someone' has more than enough 'junkboxes' but just none that holds
that sort of component (more likely low voltage / digital stuff) or
that I can find (hence my question about a box database a bit back).
;-(

Cheers, T i m

On Sat, 24 Jun 2017 21:17:34 +0100, Fredxxx wrote:

On 24/06/2017 21:05, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I think I would call them shaded pole induction motor:

https://en.wikipedia.org/wiki/Shaded-pole_motor

And you would probably be right. I forgot the key term I was thinking
of was 'induction'.

But who knows the economics of motors and control gear these days.

In this case I'm sure it's a pretty cheap and simple induction motor
(or some sort) and as you may have seen me mention elsewhere, just
span up for a few seconds! Now, it was either the cap having another
death spasm or there is an intermittent joint in the wiring somewhere
(although it all seems pretty neat, clean and undisturbed).

If when I try the replacement cap and assuming it works, I'll give all
the wiring a wiggle to make sure.

Cheers, T i m

On 24/06/2017 22:09, T i m wrote:
On Sat, 24 Jun 2017 21:17:34 +0100, Fredxxx wrote:

On 24/06/2017 21:05, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I think I would call them shaded pole induction motor:

https://en.wikipedia.org/wiki/Shaded-pole_motor

And you would probably be right. I forgot the key term I was thinking
of was 'induction'.

But who knows the economics of motors and control gear these days.

In this case I'm sure it's a pretty cheap and simple induction motor
(or some sort) and as you may have seen me mention elsewhere, just
span up for a few seconds! Now, it was either the cap having another
death spasm or there is an intermittent joint in the wiring somewhere
(although it all seems pretty neat, clean and undisturbed).

If when I try the replacement cap and assuming it works, I'll give all
the wiring a wiggle to make sure.

Do measure the winding voltage too. It will give a clue to the inductance.

Just thought, since you measured capacitance can you also measure
inductance? Though I doubt at 50Hz!

On Sat, 24 Jun 2017 23:49:15 +0100, Fredxxx wrote:

snip

In this case I'm sure it's a pretty cheap and simple induction motor
(or some sort) and as you may have seen me mention elsewhere, just
span up for a few seconds! Now, it was either the cap having another
death spasm or there is an intermittent joint in the wiring somewhere
(although it all seems pretty neat, clean and undisturbed).

If when I try the replacement cap and assuming it works, I'll give all
the wiring a wiggle to make sure.

Do measure the winding voltage too. It will give a clue to the inductance.

As I mentioned, I went to and it span up!

Just thought, since you measured capacitance can you also measure
inductance? Though I doubt at 50Hz!

;-)

I need to make the connections safe again and run it up when I'm awake
and if it doesn't actually work (or turn out to be a dry joint or some
such), I'll see what the voltage is across the run winding. At one
point I thought I saw ~12-14V (when it was ~206 across the cap) but
when I went to recheck, it was working.

Cheers, T i m

These fans have always seemed a bit of a black art. I have one and it seems
to be taking longer than it used to to get to any particular speed nowadays,
though does not get very warm. I guess eventually things just tend to wear
out but not looked inside while it still goes around.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"T i m" wrote in message
...
On Sat, 24 Jun 2017 13:09:20 -0700 (PDT), wrote:

On Saturday, 24 June 2017 21:05:13 UTC+1, T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

snip

Assuming it doesn't have brushes,

It doesn't Roger, an AC 'synchronous motor' I think they call them.

I don't think it can be. Sychronous motors lock to the mains frequency.

Ok.

Fan motors have slip.

Sure, I was probably just differentiating between a brushed and
non-brushed motor. ;-(

snip

Check. It should be here on Monday. ;-)


someone needs a junkbox.

'Someone' has more than enough 'junkboxes' but just none that holds
that sort of component (more likely low voltage / digital stuff) or
that I can find (hence my question about a box database a bit back).
;-(

Cheers, T i m

On Sun, 25 Jun 2017 09:17:06 +0100, "Brian Gaff"
wrote:

These fans have always seemed a bit of a black art.

There does seem to be a fair selection of configurations that's for
sure.

I have one and it seems
to be taking longer than it used to to get to any particular speed nowadays,
though does not get very warm.

We have one on the wall in the kitchen and I think airborne grease
gets into the bearings and makes them drag till the motor (and / or
bearings) warm up.

I guess eventually things just tend to wear
out but not looked inside while it still goes around.

I replaced the blade on mine (plastic went brittle and broke whilst
being cleaned so replaced it with an ally one) but am due to try
washing the bearings out and re-lubing them to see if that helps it
start up quicker.

Cheers, T i m

On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

T i m wrote:

On Sat, 24 Jun 2017 11:01:33 -0700 (PDT), wrote:

snip

Normally these things use a squirrel cage motor plus 2 series caps for
speed reduction.


Very sure this is stock and deffo only one cap.

It's one of these (not Clarke particularly).

https://www.machinemart.co.uk/p/clar...hrome-floor-f/

Cheers, T i m

Assuming it doesn't have brushes, and your continuity tests included the
switch, about the only thing you haven't excluded is shorted turns.
And possibly capacitor breakdown at mains voltage, so it's worth trying
the new one.

Well, after a bit of a faff (cap didn't arrive) I ordered another from
elsewhere, put it on and nothing. ;-(

The fan still 'hums' slightly when power is applied, like a coil is
getting power but the motor not spinning?

The strange thing is previously, if the fan left (for say a couple of
days) and you turned it back on again it would actually spin up ...
but then slowly slow down and stop again.

Strange ...

Cheers, T i m

T i m wrote:
On Sat, 24 Jun 2017 20:20:18 +0100, (Roger Hayter)
wrote:

T i m wrote:

On Sat, 24 Jun 2017 11:01:33 -0700 (PDT), wrote:

snip

Normally these things use a squirrel cage motor plus 2 series caps for
speed reduction.


Very sure this is stock and deffo only one cap.

It's one of these (not Clarke particularly).

https://www.machinemart.co.uk/p/clar...hrome-floor-f/

Cheers, T i m

Assuming it doesn't have brushes, and your continuity tests included the
switch, about the only thing you haven't excluded is shorted turns.
And possibly capacitor breakdown at mains voltage, so it's worth trying
the new one.

Well, after a bit of a faff (cap didn't arrive) I ordered another from
elsewhere, put it on and nothing. ;-(

The fan still 'hums' slightly when power is applied, like a coil is
getting power but the motor not spinning?

The strange thing is previously, if the fan left (for say a couple of
days) and you turned it back on again it would actually spin up ...
but then slowly slow down and stop again.

Strange ...

Cheers, T i m


Have you stripped the fan and oiled the sintered bearings?

On Mon, 24 Jul 2017 11:41:32 +0100, Capitol wrote:

snip

Well, after a bit of a faff (cap didn't arrive) I ordered another from
elsewhere, put it on and nothing. ;-(

The fan still 'hums' slightly when power is applied, like a coil is
getting power but the motor not spinning?

The strange thing is previously, if the fan left (for say a couple of
days) and you turned it back on again it would actually spin up ...
but then slowly slow down and stop again.

Strange ...


Have you stripped the fan and oiled the sintered bearings?

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Cheers, T i m

T i m wrote:
On Mon, 24 Jul 2017 11:41:32 +0100, Capitol wrote:

snip

Well, after a bit of a faff (cap didn't arrive) I ordered another from
elsewhere, put it on and nothing. ;-(

The fan still 'hums' slightly when power is applied, like a coil is
getting power but the motor not spinning?

The strange thing is previously, if the fan left (for say a couple of
days) and you turned it back on again it would actually spin up ...
but then slowly slow down and stop again.

Strange ...


Have you stripped the fan and oiled the sintered bearings?

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Cheers, T i m


Try it, you've nothing to lose.

On Monday, 24 July 2017 13:13:38 UTC+1, T i m wrote:
On Mon, 24 Jul 2017 11:41:32 +0100, Capitol wrote:

snip

Well, after a bit of a faff (cap didn't arrive) I ordered another from
elsewhere, put it on and nothing. ;-(

The fan still 'hums' slightly when power is applied, like a coil is
getting power but the motor not spinning?

The strange thing is previously, if the fan left (for say a couple of
days) and you turned it back on again it would actually spin up ...
but then slowly slow down and stop again.

Strange ...


Have you stripped the fan and oiled the sintered bearings?

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Cheers, T i m

Fans like to catch fire when they stall.


NT

On Mon, 24 Jul 2017 07:13:53 -0700 (PDT), wrote:
snip

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Fans like to catch fire when they stall.


Which is why I don't leave it on for very long (seconds) when it does
that.

Cheers, T i m

On Monday, 24 July 2017 23:37:23 UTC+1, T i m wrote:
On Mon, 24 Jul 2017 07:13:53 -0700 (PDT), tabbypurr wrote:
snip

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Fans like to catch fire when they stall.


Which is why I don't leave it on for very long (seconds) when it does
that.

Cheers, T i m

I wouldn't leave it on at all, other than during closely watched testing.


NT

wrote in message
...
On Monday, 24 July 2017 23:37:23 UTC+1, T i m wrote:
On Mon, 24 Jul 2017 07:13:53 -0700 (PDT), tabbypurr wrote:
snip

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Fans like to catch fire when they stall.


Which is why I don't leave it on for very long (seconds) when it does
that.

Cheers, T i m

I wouldn't leave it on at all, other than during closely watched testing.

Do you not have a dustbin and a few quid to buy a new one? Ohhhhhhhh, it's D
i m.
We'll have a whip-round, no petrol please, it makes such a ****ing mess.

Mine has a safety feature in that if you touch the fan cage the motor stops but continues to hum. This feature broke once and the fan just hummed when I switched it on. There was a connection to the frame that had gone open circuit. I cant remember the details of how it worked but there was a single connection to the frame and some sort of proximity detector.

On Mon, 24 Jul 2017 17:22:53 -0700 (PDT), wrote:

On Monday, 24 July 2017 23:37:23 UTC+1, T i m wrote:
On Mon, 24 Jul 2017 07:13:53 -0700 (PDT), tabbypurr wrote:
snip

No, no need, the fan blade spins very freely and the whole thing looks
like new?

Fans like to catch fire when they stall.


Which is why I don't leave it on for very long (seconds) when it does
that.

Cheers, T i m

I wouldn't leave it on at all, other than during closely watched testing.

More literal left-brainer translations eh ...? ;-(

I *don't* leave it on, I only have it on long enough to test it (duh).

Cheers, T i m

On Tue, 25 Jul 2017 01:35:49 +0100, "bm" wrote:

snip

Do you not have a dustbin

Yes, it's where I keep all your advice and opinions.

and a few quid to buy a new one?

Why would I buy my mate a new one? I'd just give it back to him to
throw in the electrical recycling skip at the tip?

snip drool

Cheers, T i m

On Tue, 25 Jul 2017 02:40:30 -0700 (PDT), JohnW
wrote:

Mine has a safety feature in that if you touch the fan cage the motor stops but continues to hum.

Ooerr. Hmm, often when I've been testing it it's just been resting on
the sofa (on it's cage).

This feature broke once and the fan just hummed when I switched it on.

Ok.

There was a connection to the frame that had gone open circuit. I cant remember the details of how it worked but there was a single connection to the frame and some sort of proximity detector.

Whilst it would be good to think this one had such a feature, I've had
it all apart and didn't see anything that looked like it would do that
('electronics' etc). ;-(

Cheers, T i m