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Old 12th February 2002, 11:59 PM   #1
jteef is offline jteef  United States
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Default Silent Fans

How difficult would it be for the DIYer to build one of the fans they are advertising at places like sharper image / hammacher-schlemmer. "Ionic Breeze" is I think what sharper image names their fans.

Exactly how do they work? I remember doing a homework problem similar to this (only using water instead of air) way back in my freshman emag class. I dont remember any of the details though.

Would something like this be feasable for all of us not wanting to spend exorbitant amounts of money on heatsinks to cool our aleph's ?

I didn't have to take a thermodynamics class and dont know much about heat transfer. Where can I find out how X amount of air flow will aid Y heatsink?

Ideas?

Thanks

jt
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Old 13th February 2002, 10:10 AM   #2
jteef is offline jteef  United States
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Update:

The most relevant patent I found on this is 4,789,801 by ZenIon Industries. Unfortunately, it is not as descriptive as Mr. Pass'.

He claims to have nonmechanical fans capable of 400CFM. That would be great!.

I would still like to put something together my self in order to integrate nicely with the amps.

I am still very open ideas, comments or criticism.

jt
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Old 16th February 2002, 05:01 PM   #3
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Default Silent Fans

Years ago I found something that worked but never realy knew why. By placing a cap in the 1uf range in seriese to a small 115v
boxxer style fan I was able to run it at a redused speed. This was realy strange as a .5uf cap wouldn't run it at all .8uf seemed to run it at about 300rpm 1uf seemed about half speed and 1.5uf
was full speed.


Still puzzled !

Bob
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Old 16th February 2002, 07:36 PM   #4
subwo1 is offline subwo1  United States
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Bob,

Maybe I can help clarify what happened. When you placed the capacitor in series with the fan, you were increasing the total impedance of the circuit. That reduced the current that was able to flow into the fan motor

Smaller capacitances offer higher impedance to ac as would a larger resistance. But they differ from each other in how they they impede the current.
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Old 21st February 2002, 05:12 AM   #5
Sud is offline Sud
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Lightbulb Low noise fans

jteef,

A simple way to reduce noise from fans is to run them at reduced voltage. Run a 12V DC fan on 6V and it will be very quiet. The more voltage, the noisier it gets. Note that most fans need about 3V or so to spin.

The downside is that the CFM reduces too. If you need a certain CFM, instead of buying a small fan that delivers the desired CFM at full voltage, get a bigger fan that delivers much more than your desired CFM at full voltage. Run it at reduced voltage and you'll still get your CFM but with much less noise.

The noise from fans increases dramatically near its maximum voltage.

Sud
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Old 19th March 2002, 12:53 AM   #6
Lenin is offline Lenin  United Kingdom
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Default Shutting the door after the horse has bolted

Yeah, of course, reducing the fans supply voltage will reduce noice (it increases logarimicaly as it approaches full voltage by the way).

But surely the thing to do is to get an extremely low noise fan in the first place. Papst do a range of 12db fans (most sizes and voltages). Together with a supply set at half the rated voltage will hopefully shut up the worlds "fans are noisy" naysayers
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Old 19th March 2002, 02:14 AM   #7
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Hello All,
Big blades plus slow rotation = quiet.

Regards, Eric.
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Old 19th March 2002, 02:21 AM   #8
JoeBob is offline JoeBob  Canada
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Small blades + slow rotation = quiet
big blades + slow rotation = quiet, but still has a usefull CFM
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Old 19th March 2002, 06:50 AM   #9
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What I have used in the past is 2 x 120 volt fans in series. We have here 220 V. They are very quiet and enough air flow.
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