Fan Speed Control

ajriding wrote:
Also, side question.. what is difference in having the switch or controller on the neg side vs the positive side (other than ability to turn off the wire current)?
Is this controller switching the neg side? Maybe just so if it does burn out that the full 12v can still flow through? I know an on/off switch means nothing to the fan, but the control on neg or pos side, is that different?

Most cheaper PWM controllers are switching the negative/ground side of the circuit for the speed control--and indeed many not cheaper ones as well. This mainly has to do with the characteristics of available switching transistors; N channel MOSFETs, which are what are used to switch the low side, inherently tend to have better performance than P channel MOSFETs that you'd use to control the positive side. The same generally applies to other types of semiconductor switching devices, too. To get equal performance from the high side switching, you'd need to use more expensive switching transistors...and often slightly more complicated control/transistor drive circuitry as well.

It makes no difference at all to a DC load which side of the circuit is being switched. In fact, there is no way at the load to tell which side is being switched if you don't use some additional voltage or ground reference.