Recently, I’ve been playing around with old computer power supplies. Naturally, that led me to other components of the computer, namely, the cooling fan. These fans are driven by a brushless DC motor system. This is to achieve a reduced sound and higher efficiency compared to a brushed DC motor system such as those you would see (or hear) in printers, air conditioners and RC cars. Computer fans can range from very simple to kind-of-simple with 2, 3, and 4 wires coming out of it.