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[kurupetos]

Thank you all.

[Sotos]

Any current not going to the fans must be emitted as heat via a resistor so you've basicly increased the heat inside the case.

I am not an expert in this field but I can't understand your theory here. If there is less demand for energy doesn't this mean that less energy will be consumed? The way you say is like the power supply always takes the same amount of energy regardless of how much energy the devices of the computer consume and then turns the surplus into heat. That can not be true because I know for a fact that on a laptop you can save energy and make the battery run longer by having your hard drives spinning slower or making your LCD dimmer!

[Get Real!]

Any current not going to the fans must be emitted as heat via a resistor so you've basicly increased the heat inside the case.

I am not an expert in this field but I can't understand your theory here. If there is less demand for energy doesn't this mean that less energy will be consumed? The way you say is like the power supply always takes the same amount of energy regardless of how much energy the devices of the computer consume and then turns the surplus into heat. That can not be true because I know for a fact that on a laptop you can save energy and make the battery run longer by having your hard drives spinning slower or making your LCD dimmer!

To simplify things we need to stick to analog electronics and take a dimmer switch, which is the same as a normal switch except it has a variable resistor (the knob you turn). As you rotate the knob anticlockwise the resistance is increased and so the current going to the light bulb is decreased thereby making the lamp fade but this “stolen” current has to go somewhere and it is dissipated in the form of heat using a component like a ceramic resistor.

Every component has a preset wattage or power consumption and the only way to decrease that power usage is to “steal it” via a resistor (to resist a portion of that current) which makes the resistor heat up to dissipate that wattage. The whole power requirement of that component is still being consumed but a portion of it redirected to a resistor. The ACPI used in laptops is a different technology altogether.

[miltiades]

In my experience dealing with fan motors for refrigeration , ice machines , convection ovens and other appliances requiring a fan motor which becomes noisy , is that the bearing or armature has gone . WD 40 might temporarily alleviate the noise but it will not cure it . Change to a new one for trouble free ...fun .. !!!

If the armature was gone it wouldn’t work at all! A worn out bush is easily identifiable because the fins would begin to scrape the sides if the fan is housed or wobble if not.

A slightly worn armature would still work but rather noisy , but you are correct that if the armature is burned out the motor would not work.
Noise from the motor is usually the bearing.

You are confusing the armature with the motor's brushes that wear; good motors have replaceable brushes btw.

I'm not confusing the armature at all . We do change brushes , especially on machinery such as Fruit Juicers , extractors , and most other motors. The brushes once totally worn render the appliance unworkable , the armature behaves in a way the same as a motor car's crankshaft in that a partly worn armature , one that has "body" damage , "scratches "on the body will fail to perform for long and will eventually fail to function.

I'm not an engineer but over the years of involvement with repairs of an assortment of Catering equipment , by necessity you learn something.

[Oracle]

Open a window .....

[Get Real!]

In my experience dealing with fan motors for refrigeration , ice machines , convection ovens and other appliances requiring a fan motor which becomes noisy , is that the bearing or armature has gone . WD 40 might temporarily alleviate the noise but it will not cure it . Change to a new one for trouble free ...fun .. !!!

If the armature was gone it wouldn’t work at all! A worn out bush is easily identifiable because the fins would begin to scrape the sides if the fan is housed or wobble if not.

A slightly worn armature would still work but rather noisy , but you are correct that if the armature is burned out the motor would not work.
Noise from the motor is usually the bearing.

You are confusing the armature with the motor's brushes that wear; good motors have replaceable brushes btw.

I'm not confusing the armature at all . We do change brushes , especially on machinery such as Fruit Juicers , extractors , and most other motors. The brushes once totally worn render the appliance unworkable , the armature behaves in a way the same as a motor car's crankshaft in that a partly worn armature , one that has "body" damage , "scratches "on the body will fail to perform for long and will eventually fail to function.

I'm not an engineer but over the years of involvement with repairs of an assortment of Catering equipment , by necessity you learn something.

Milti, the armature gets dirty (soot) from the constant rubbing with the brushes resulting in loss of conductivity but it can be easily cleaned with a solvent and made nice and shiny again. The brushes are the ones that wear because they are intentionally made of a much softer copper material to protect the armature. Even if the armature gets a bit thinner after many years of use, the spring tension of the brushes will ensure that good contact is still made with it.

Of course, it may be in your interests to REPLACE the part than clean it...

[Zorba]

I have a noisy fan.
Will reducing the voltage (e.g. from 12V to 9V) reduce the speed, and therefore the noice?

It seems like it since:

P = V . I = F . v (Power = Voltage * Current = Force * velocity)

What do u think? Any advice?

Since the other two have gone off on a technical debate,I was wondering if you reduced the voltage and the revs were reduced,would it not be less effective in cooling ?

[miltiades]

GR Wrote:
"""""Of course, it may be in your interests to REPLACE the part than clean it... """"

I have an engineer that has been with me since 1995 , Tom .
The other day he was given a job to do in Baker Street , central London , it was a job requiring the repair of the convection oven fan in a 6 radiant 3- phase electric oven.
Tom is as straight as you will ever encounter , so if lets say the only problem the oven had was a fuse , Tom would replace and charge just for one fuse plus our call out charge . Never in a million years would Tom ever stretch out the job or charge a customer unnecessarily for work that was not required.
I ought to say that Tom is a brilliant engineer that could have been at the very top if it wasnt for the fact that he is not the least interested in material possesions .
Tom got to Baker street station by train carrying his toolbox and proceeded to the restaurant that the repair was needed .
It turned out that some one had inadvertently switched the oven off from the mains , Tom found that pretty quickly and switched the oven's mains back on .
He rung me to say that I can not really charge a call out charge but he would charge just his train fare £5.60 !!

Our call out charge is £90.00 for the West End .
No wonder I'm skinned ..

[Zorba]

No,you are skint, TOM should be skinned

[kurupetos]

I have a noisy fan.
Will reducing the voltage (e.g. from 12V to 9V) reduce the speed, and therefore the noice?

It seems like it since:

P = V . I = F . v (Power = Voltage * Current = Force * velocity)

What do u think? Any advice?

Since the other two have gone off on a technical debate,I was wondering if you reduced the voltage and the revs were reduced,would it not be less effective in cooling ?

No cooling involved, only drying the bathroom since it does not have any windows.