Question involving fan control.

[Balthazar]

I installed a 92mm case fan in my case today and while the cooling is very effective, its a smidge on the loud side.

This is the fan.

So I went to RatShack to snag a pot and knob to make a control, not being entirely certain what type of pot to get I asked the guy at the counter and he recommended this:
Resistance: 100K Ohms
Rated Power: .25 Watts
Sliding Noise: <47mV
Total Rotation: 300 deg. +-5 deg.

Part #: 271-092

So, my question is....will this work for my fan?

Thanks in advance guys! (I've made several volume control boxes before but never a fan control so I appreciate the help).

 

[Zepper]

It's easy to tell what size pot you need. Ohms of fan = Volt rating of fan / Amp rating of fan . You will want a resistor a bit lower than the resistance (Ohms) of the fan.
. 110 kOhms is way too high as most 80x25 12V fans will be 100 Ohms or less. So a 100 Ohm, linear taper pot or rheostat, rated at a minimum of 2 Watts will be usable for most fans that draw up to 0.45 Amp or so at 12V.
. Most 12V fans won't run at less than 7V so check for stall position on the dial and leave a conservative cushion. If your fan draws 0.5 Amp or more, then you will need both a lower Ohm rating and a higher Watt rating.
. I'm thinking of doing a resistance chart for every .05 Amp step of 12V fans - easy to do w/ a spreadsheet (or even a BASIC) proggy. I could probably do it in my head, let's see:
For 12 Volt Fans:
Amp------Resistance
---- Rating of
------ Fan
-------- ------------
0.10A = 120 Ohms
0.15A = 80 "
0.20A = 60 "
0.25A = 48 "
0.30A = 40 "
0.35A = 34.3 "
0.40A = 30 "
0.45A = 26.7 " At this point only 25% of 100 Ohm pot rotation could be used.
0.50A = 24 " From here a 50 Ohm or less pot should be used rated at 5 Watts up.
0.55A = 21.8 " The 15 Ohm 15Watt rheostat from allelectronics.com
0.60A = 20 " would probably work for all from about 20 Ohms down.
0.65A = 18.5 "
0.70A = 17.1 "
0.75A = 16 "
0.80A = 15 "
0.85A = 14.1 "
0.90A = 13.3 "
0.95A = 12.6 "
1.0A = 12 "
----------------------
Note well: Make sure the pot/rheostat is in series with the fan (IOW, you use only two legs of the pot, the middle and one end - not all three), not in the typical series/parallel configuration you'd use in a volume control circuit as you don't want the additional load.

There ya go...
.bh.

 

[Balthazar]

Great info, I finally tracked down a link to a site that had a article about making a fan control knob but this info here is alot more my speed (i.e.: not just "buy this and this and solder this").

Thanks a bunch!

 

[Zepper]

YW, and you want to check on the working voltage range of your fan on the mfr's web site. One of the 120mm fans I just bought supposedly has a working range of only 10.2-13.2V where most will have a much larger working range (7-13.2V) is typical. That info will help in determining the size of pot, as you will probably want to be able to use a significant portion of the rotation range of your pot.
.bh.