I'm picking up a few (3) 2-pin 12v fans to put into a isolation box I am making for my present computer. I want all the fans to run simultaneously but want to be control them via an external pot. The problem lies in how to control them all at once. I haven't been able to find a single variable resistor that could control all three together which means I might have to wire them in parallel/series. I know the impedence would start changing drastically, but is it feasible if I use an external 12v power supply?