Domestic fan speeds.

I have a couple of domestic fans, that we have on in the bedroom during hot nights - calm down, I am referring to the weather !!

They are both too noisy even at their lowest speeds. I have opened both up but the speed selector switches are just plain switches that feed about four cables that go up to the motor, no electronics. So I am wondering how the different speeds are achieved? Different combinations of windings perhaps?

I was hoping I could change a component to get a slower speed. The fans are not expensive or sophisticated. Can anyone tell me how the different speeds are likely to be controlled?

Thanks

Edited By John Doe 2 on 11/08/2022 16:23:02

Answered my own question; the black rectangular item is the start capacitor and the coloured wires must go to different field coils to give the different speeds.

So looks like I cannot lower the speeds without building an electronic speed control Pity.

What would happen if a power diode was in the power supply to the fan?

Bring back the Variac!

I can recommend a fan I purchased recently from Amazon, just before the first heatwave. It's virtually silent on the lowest speed setting and was very welcome through those 'hot nights'.

It was aound £70 but worth it I think. It oscillates left and right and also upward and back to level, all at the same time if desired. The icing on the cake is a remote control. I won't post a link as it may break the site rules but if interested, look for Iris Ohyama on Amazon.

Ed.

For a number years now we have had ceiling fans fitted in two of our bedrooms, they have 3 speed settings and are invaluable during any hot weather, we use them throughout the summer months as we are on the South Coast and it is always the warmest area of the UK. When the fans are working our cats come up on the beds to bask in the cool breeze, they know where to be. With the prospect of our summers getting ever hotter I would encourage those that suffer when it gets hot to seriously consider fitting ceiling fans, I grew up in the Far East so am no stranger to ceiling fans. Dave W

The motor would draw excessive current. It needs AC.

End result would be a blown fuse at best and a fire at worst. Mostlikely smoke followed by blown fuse.

Robert G8RPI.

Ear plugs ?

I thought it was different values of capacitance that are switched to the single winding - most capacitance = slower speed, less capacitance = medium speed, no capacitance = full speed..

Nigel B.

In principle, induction motors only work at a speed a bit below the synchronous value, eg about 2800 rpm for a two pole 50Hz with theoretical sync 3000 rpm. The speed varies slightly with load, but must normally be quite near "2800 rpm" as the torque quickly falls off beyond some point.

However, in the case that the load is a fan, the torque needed falls even quicker as speed reduces, so if the motor power is reduced it can be stable at a considerably reduced speed. If the speed reduces a bit, the fan torque needed reduces more than commensurately. Hence this type of multi speed fan, but it is likely the designer will already have maximised the practicable speed range, so probably no scope to run it slower.

As someone who lives in the tropics under and next to fans constantly for half the year, I reckon just persevere with your current fan. After the first week you get used to the noise and do not notice it anymore.

I wonder if smoothing the edges of your fan blades with emery paper would quieten it down a little bit?

Dyson and others do make "bladeless" fans that are relatively silent. They have an annular discharge ring with some kind of concealed blower in the bottom housing. As always, the more expensive the better they work.

The motor will also have a rotor designed for a more linear torque/speed characteristic so speed can be controlled by varying the main field ampere-turns through tap switching.

Thanks all, that's what I thought. There is only one capacitor with just two terminals, so I think the three speeds are not achieved by different capacitor values, only by switching different coils in the motor itself.

We do have a high quality ceiling fan that is much quieter, but have just moved house (again), so it is still in its box and not fitted yet.

Ironically I am waiting for cooler weather before I go up into the loft to fit a reinforcement plate to mount the ceiling fan in the bedroom. If I went up there now in this heat, I would expire ! Catch 22.

I might try smoothing the blade edges of the noisy floor fan though in the meantime.

I don't know a lot about induction motors, would a variable phase-angle type dimmer switch work, or would it cause motor overheating?

Edited By John Doe 2 on 12/08/2022 07:41:57

My experience living in Thailand is that at low speeds the fans are very quiet until the bearings start to fail. And if you want to play with speed control you could try using a variable frequency inverter drive. But I think a larger diameter fan will probably be quieter and cheaper.

Variable phase angle type dimmers are used for fan speed control but may not give much lower speed on a multispeed fan. You want a really basic one, a modern unit designed for energy saving lamps etc may not work.

Robert G8RPI.

You can still get those but the cost would probably buy a deluxe fan.

Edited By V8Eng on 12/08/2022 10:16:54

One suggestion, are the bearings dry? Oilite bushes do dry out. Second, a warning, the guts shown look similar to those on my floorstanding bedroom fan. When trying to readjust the position of the head unit, the plastic cover crumbled. OK it's a few years old now but one can only assume (?) the UV stabilisation of the plastic wasn't a priority to the far eastern manufacturer.

It was off when this happened.

Regards Ian.

Sorry, I should have been more clear, it is the wind noise that is the problem. The fans themselves are in good condition - it is just that their lowest speed is too high for us sleeping at night.

As soon as I can fit our ceiling fan, the problem will go away, but that will take a day or so to fit, and that will happen only after the temperature in the loft has reduced. I was hoping for a quick fix in the meantime.

Oh well.

Edited By John Doe 2 on 12/08/2022 10:33:38

I've noticed a line of grime along the trailing edges of our fan blades. I'm guessing it's due to turbulent flow into the partial vacuum created by the moving blades, though I'm a bit puzzled how they pulled so much dirt in about 2 years' summer-only use.

Presumably sharpening the trailing edge and at least tidying up the leading might both reduce noise and dirt accumulation?

Change section from Clark Y to Eppler 374 or RAF curved plate. 

Regards Ian.

Edited By Circlip on 12/08/2022 10:59:36