Automatically Switching On The Fan
Now we can tinker a bit, and build our own sensor-controlled on and off switch. The switch kit needs at least 12 V DC. Getting that from one of the power supply's four-pin connectors is easy enough.
In the interest of clean connections, the manufacturer of our switch tins the end of its wires.
The included sensor (a thermistor) can be attached with a cable up to one meter in length. We used about 30 cm of common copper litz wire and held the strands together with electrical tape.
The thermistor’s soldered connections need to be isolated properly so that they don't touch anything metal. This can be done with shrink tubing or just some electrical tape, though you should keep tape away from the hotter parts of the heat sink. The thermistor is glued onto the cooler with some of the same adhesive used to attach RAM sinks. If all else fails, wrap the thermistor in aluminum foil and attach it to a heat pipe using a cable tie. Whichever way you go, you'll want to secure the thermistor before you install the SilverStone heat sink to avoid getting your hands scratched up.
Pick the right temperature for activating the switch by applying a load to the system and watching its thermal status using Core Temp or AIDA64. In our case, we picked 40 degrees Celsius, measured at the back of the Heligon HE02 using an infrared thermometer.
The biggest risk in buying a hobbyist-oriented kit like ours that probably wasn't QA'ed very well is the potential of a dead component. We had to exchange it twice until we found one that worked the way it was supposed to. The key is to set on and off temperatures far enough apart, with the off temperature much lower, so that the switch doesn’t keep triggering on and off quickly (you'll know when you hear the relay click over). We had a lot of fun tinkering with this.
