Simple way to reduce RPM on this fan?

[frascati]

Fan runs constantly, even when the air exhausting the exit is cool. I opened the case hoping to find everything deeply clogged with dust but there was very little, certainly not enough to be causing such an issue. Noisy fan is a common complaint on this model hp110mini.

From what I understand thusfar the red is 5v pos, the black is ground, the yellow is RPM signal return to the motherboard.

I've checked and there appears to be no way to regulate the voltage/speed via GUI. I have read a few webpage prescribing as simple as a series resistor ranging from 10 to 300 ohm (depending upon who's math you have faith in) as well as applying a three pin IC voltage regulator (which sounds ideal, but there are thousands to choose from).

I'd like to drop the rpm (unknown) almost 50 percent.

Any suggestions?

 

[CocaCola]

You will have to experiment with a series resistor (different values) and dial it in to the speed you want, you can also experiment with a series diode or two as well to slow it down... In both cases you are starving the fan of what it wants to run, so it's a balance act too much and the fan won't start up,or won't have enough power to overcome a few dust bunnies clogging it up over time...

You are going to want to use at minimum 1.5Watt rated resistors, remember you can parallel resistors to up the wattage rating...

Example four 200 Ohm @ 1/4 Watt resistors in parallel will be equivalent to a single 50 Ohm @ 1 Watt resistor...

Personally I would try a series 1n400x diode or two first...

 

[KrisBlueNZ]

Yeah, what CocaCola said
A suitable diode would be 1N4001 (or anything from 4001 to 4007). You didn't put your location in your profile (the option is there for a good reason, you know) but assuming you're in America, you can get them from Radio Shack: http://www.radioshack.com/product/index.jsp?productId=2062589
Put one or more of them in series in the red wire. Each one drops about 0.7V. Connect them with the cathode (stripe end) towards the fan.

 

[geekygenius]

Being a complete noob with electronics, I'd like to know why PWM wasn't suggested. Was it because its simpler to add a series resistor, or does it have something to do with power?

or am I just a complete nutcase for suggesting something like that.

 

[(*steve*)]

PWM would be ideal if the goal was to have a continuously variable fan speed, and if there was room to place the circuit.

Here, the aim is to reduce the fan speed a little, and almost certainly do it in an environment where there's almost zero spare room.

A diode won't take much room and can be wired into the cable. It provides better torque than if you used a resistor.