The other day I had a scare when my Xbox 360 refused to play a disc. After doing some searching around on the internet the most likely cause was that it had overheated and faulted. It turned out that the power cable was loose but regardless it got me thinking about how to best regulate the temperature of my home theater equipment. All the electronics are in an A/V closet (well sort of closet). The face is open but still there is not much air flow through there. I figured I would just throw a fan behind the equipment blow foward. I had a pretty beefy A/C fan already so I went ahead and mounted it in the closet using foam under the mounting brackets. I plugged the fan into the power jack on the back of the receiver so it would turn on when the receiver was on.

The problem was that the fan was still too loud. It was clearly audible from the couch. Normally this would not bother me too much but I just finished a couple years worth of work to get the home theater just where I wanted it so I couldn't stand for the extra noise. I decided that I would add a temperature control to it so that the fan would be on when the receiver was on AND it was above a certain temperature. If the temp was that high I was likely beating on the system and would not notice the fan noise.

I picked up a thermostat that works very simply. It completes the circuit at a configurable temperature, anywhere between 30 and 140 degrees f. I added it on the positive wire of the fan and hooked everything back up expecting to be very please with myself. In actuality the fan was doing exactly the opposite of what I wanted. It was on all the time until I hit a high temperature then it turned off. Oops.

I headed off to radio shack to get an A/C relay so that I could use the thermostat output to control a normally open relay. Now when its cold the thermostat flows current which closes the relay and keeps the fan turned off. Once it heats up the thermostat stops flowing current which opens the relay and causes the fan to kick on.

All in all this was a quick project that probably does not deserve its own webpage however I had not added anything to the projects section for a while now so here it is.

Components

Stego Thermostat, 01140.9-00
AC 10 amp double pole double throw relay from radio shack, 275-217
random AC fan
old extension cord without ground

Photos

All wired up

The completed circuit, ready to hook up to the fan. I still need to insulate the bare terminals on the relay.