Rheostat: how many Ohms for mulitple fans?

[Lancelot]

I'm adding three 80mm fans to my case, is it possible to regulate all of them together using one Rheostat, or should every fan get it's own? And how many Ohms should the Rheostat (or potentiometer) be anyway? I can't seem to find the article that was posted about it...

[ken257]

Right now I am using a 25 ohm rheostat (all radio shack had) it is a little course on the adjustment I think maybe 10-15 ohms would be better. If you want to control multiple fans it should be ok as long as you get a rheostat with a high enough wattage.

[komodo]

www.ocmod.com may help, one number of LM 317T, one number of 1kohm 0.5W rheostat and 100ohm resistor, Can handle upto 1.5A current, sufficient to handle ur three no of 80mm fan and cost 2 or 3 us dollars. sounds good to u.

[Hoot]

The LM317 will not output the full 12V. The output is typically Vin-1.2V, or about 10.8V. Most fans develop their greatest RPM in the last volt or two. Just a caveat.

To chose the right value of rheostat, you have to consider the amount of current the fan(s) consume. If you can pass along the rated current or wattage, I can help you determine the best value. For example:
If the total current consumption is .5A (6W) and you want to vary the voltage from 12 down to 8V, a 10 ohm rheostat is a good choice. Swiftech sells them. If the current consumption is .25A (3W) you would use a 20 ohm. It scales that way.

Hoot

[Lancelot]

I used 1ampere diodes! (1N4007) I soldered three of them (serial) into one of the powerleads to the fans. This lowers the voltage by 1,8 which is exactly enough to take away the noisy whining :D

[Hoot]

A homemade zener diode! ;D

Hoot