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Old March 16th 05, 09:10 AM
CBFalconer
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wrote:

I would like to know the way to reduce the speed of a fan inside a
small device in order to cut down the noise from the fan. If I
understand this correctly, I am supposed to do this by undervolting
the fan from 12-volt it is now to something like 6-volt using some
kind of "inline resistor" or someting. I can soldering wires
together. But I really don't know much about resistor and such. I
am hoping someone can give me the "exact" information about the
way to do this.

.... snip ...

- The fan is rated as 12V and 0.6 watt with two wires.
What type of "inline resistor" should I use? I am
under the impression that inline resistor is rated
by "ohms". Can someone give me a RadioShack
product-number or something like that?

- Which wire should I solder the inline resistor to the
fan? Red-wire or the blue-wire of the fan?

- Does this matter which way I orient the inline resistor?


Well, at least you know you don't know anything about electricity.
If the figures you give are accurate (which they aren't, they are
probably maximums) you want about the same ohmage as what the fan
appears to be. This would be about 12 v. / 0.05 A = 240 ohms. All
that really does is give you a ball park number. You may want
anything from about 100 ohms to that. They should probably be at
least 2 watt rated for safety, but have virtually no tolerance
requirements. Get a set of 2 watt carbon resistors, worth about 5
to 10 cents each (but expect to pay more unless you can raid
someones junk box), say 100, 150, 220, 330 ohms and try them out.
No, it doesn't matter which lead they appear in, nor which
direction they are connected in. Ohms and watts are an adequate
specification, and you don't need anything better than 10 or 20%
tolerance.

To try them out you don't need to solder anything. Clip leads with
alligator clips on the ends will be useful. Feel the resistor
while running with it - it should not be too hot to touch. If so,
it is a sign you need a higher wattage. But I expect 2 watts will
be more than adequate.

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