[SamT]

Right - bit of an odd one that I'm sure some electrical boffin on here might be able to guide me on.

Just bought (off the internet from italy, so i don't expect any customer service) a rather nice and expensive cooker hood and had it fitted in our lovely now kitchen.  Get me.

It was chosen on the basis if it having a low noise rating compared to other fans.

On first trying it, we were blown away by the noise, its like a Hercules transporter plane taking off, on its lowest setting.  Instead of 1,2 3 on the power settings, it should be Hercules, Sea King, 747.

Its published dB was 52,  On its lowest setting, my App on my phone was measuring 75dB at 1m away (the level at which employers have to inform and train staff on the dangers of noise etc).

Building regs states that it should be pulling about 30l/s air flow.  Measured on the outlet outside it was pushing 65 odd l/s, so twice the rate it needs to be.

It cant really be replaced (built into kitchen) and as mentioned not expecting any kind of customer service.

So.....

I'm wondering if I can fit some sort of variable speed controller, in line to the motor, to turn the damn thing down. At the moment, we're just not using it as its too loud which makes it a very expensive, pretty, but ultimately useless addition to the kitchen.

attached are some pics showing some figures for the electric gubbins inside, but electrics is not my bag.
From googling, I expect the motor will be a brush less induction motor. Looks like there are two cables going to the motor.

Any clues as to whether or not this would be possible/feasible.

https://imgur.com/a/Y2kbavE

[Paul B]

Isn't that flow-rate too high to be over a hob i.e. 30l/s over a hob or 60l/s elsewhere in the kitchen (is it over a hob?; Gas/Elec?)?

I'm just wondering if there's a setting for where it's placed somewhere on the unit? Edit: the instruction manuals aren't very useful!

[SamT]

Yep - that's Part F regs - 30 over a hob - 60 elsewhere - though they're minimum flow rates, no harm in exceeding them.

Its just a question of the noise really.  I'm going to have a tinker in there tonight and see if I can see what wires go where, also open up the box that seems to contain the speed gubbins that sits between the 3 buttons on the front, and the motor.

Also try and  suss out why there are two wires plugged into the motor?? 

[tomtom]

Presumably the wattage isn’t that high for the fan - as it’s just an extractor. Could you run the power to it through a regular domestic dimmer switch?

Or is that a BAD idea?

[Somebody's Fool]

Is it ducted anywhere?

Vibrating pipes can often make them a lot louder than they’re supposed to be.

[moose]

Yep - that's Part F regs - 30 over a hob - 60 elsewhere - though they're minimum flow rates, no harm in exceeding them.

Depends if there's an open flued solid fuel / oil burning / gas stove nearby; I'll see your Part F and raise my Part J!

1.20  Extract fans lower the pressure in a building, which can cause the spillage of combustion products from open flued appliances. This can occur even if the appliance and the fan are in different rooms. Ceiling fans produce air currents and hence local depressurisation which can also cause the spillage of flue gases from open-flued gas appliances or from solid fuel open fires.

In buildings where it is intended to install open-flued combustion appliances and extract fans, the combustion appliances should be able to operate safely whether or not the fans are running. A way of showing compliance in these circumstances would be to follow the installation guidance below, and to show by tests that combustion appliances operate safely whether or not fans are running.

(a) For   gas   appliances: where a kitchen contains an  open-flued appliance, the   extract rate of the kitchen extract fan should not exceed 20 litres/second (72 m³/hour).

[Fultonius]

Since you have 3 peed settings, it's definitely a variable speed fan. It kind of depends how the fan is currently controlled, whether it's pulse width, or variable resistor.

I'm guessing you could probably get away with just wiring another speed controller in series, but it might be possible just to dump some power by sticking a reasonable sized resistor in line?

[moose]

Since you have 3 peed settings, it's definitely a variable speed fan. It kind of depends how the fan is currently controlled, whether it's pulse width, or variable resistor.

I am not an electrical engineer, but my prodding of their remains suggests that 3 speed extract fans often have 2 sets of windings - small and large.  So you could get low speed by energising the small windings alone, medium from the large windings, fast by energising both?

[SamT]

Yep - that's Part F regs - 30 over a hob - 60 elsewhere - though they're minimum flow rates, no harm in exceeding them.

Depends if there's an open flued solid fuel / oil burning / gas stove nearby; I'll see your Part F and raise my Part J!

Spot on Moose, but whilst we have a stove, its in the front room, not the kitchen, I'm reasonably satisfied that the hallway between is suitable 'leaky' to not be an issue with negative pressures.  All the more reason though to 'detune' the thing.

Since you have 3 peed settings, it's definitely a variable speed fan. It kind of depends how the fan is currently controlled, whether it's pulse width, or variable resistor.
I'm guessing you could probably get away with just wiring another speed controller in series, but it might be possible just to dump some power by sticking a reasonable sized resistor in line?

This is kind of the thing I was thinking.  I expect its an induction motor, and whilst I know very little about power electrics/motors etc, my googling suggests that you can't just reduce the resistance on an induction motor (things get hot I think!!)  as the speed will be controlled by the frequency, so you need some clever box of tricks to reduce the frequency, that will ultimately reduce the speed of the fan??

Elsewhere, someone has pointed me in the direction of a Faber importer based in Sheffield, (KitchenEX) so I'll be calling them today. 

Cheers for the contributions so far 

[highrepute]

Since you have 3 peed settings, it's definitely a variable speed fan. It kind of depends how the fan is currently controlled, whether it's pulse width, or variable resistor.

I am not an electrical engineer, but my prodding of their remains suggests that 3 speed extract fans often have 2 sets of windings - small and large.  So you could get low speed by energising the small windings alone, medium from the large windings, fast by energising both?

I'm an electronic engineer, slightly different to electrical.

Moose is right. It's an AC motor not DC, if it were DC then fultonius would be right.

It's very hard to change the speeds of this type of motor. I think reducing the number of windings would do it but that's no easy task. Reducing the voltage to the thing might do it but it would very quickly be unhappy with the wrong voltage and also you're playing with 240v and it not easy to just make volts disappear.

The little white box in your picture is just for LEDs I think.

My recommendation would be buy a lower wattage fan part and wire that in. And like Paul b says check it's not something rattling making all the noise.

A lot of guessing in that post and as always I could very easily be wrong.

[moose]

Moose is right.

There's a first time for everything!  It's often hard for me to make an informed judgement... my job means I see a vast array of equipment... unfortunately it's usually burned away beyond recognition!

[Fultonius]

Since you have 3 peed settings, it's definitely a variable speed fan. It kind of depends how the fan is currently controlled, whether it's pulse width, or variable resistor.

I am not an electrical engineer, but my prodding of their remains suggests that 3 speed extract fans often have 2 sets of windings - small and large.  So you could get low speed by energising the small windings alone, medium from the large windings, fast by energising both?

I'm an electronic engineer, slightly different to electrical.

Moose is right. It's an AC motor not DC, if it were DC then fultonius would be right.

It's very hard to change the speeds of this type of motor. I think reducing the number of windings would do it but that's no easy task. Reducing the voltage to the thing might do it but it would very quickly be unhappy with the wrong voltage and also you're playing with 240v and it not easy to just make volts disappear.

The little white box in your picture is just for LEDs I think.

My recommendation would be buy a lower wattage fan part and wire that in. And like Paul b says check it's not something rattling making all the noise.

A lot of guessing in that post and as always I could very easily be wrong.

Oh aye, good point. Should post about things I only vaguely understand 5 minutes before bed.....

I'm guessing a frequency converter is going to be a bit spendy!  (we have a 7 MW one at work, but I think that's a bit OTT...) 

[highrepute]

Yes. Changing the frequency will work too. I have a feeling that's the best way actually now you mention it but don't understand it enough to say how.

[Fultonius]

This would probably work:

https://www.ebay.co.uk/itm/362593239979

Finding somewhere to put it might be the issue!