HI, I'm very new to all of this electronic stuff and I'm looking for some direction. I'd like to put a temperature controlled on/off switch on the 12v lead to an 80mm cooling fan. (Bi-metal switch?) I don't know what they are called, and I don't know where to look to find them. I've seen some that are silver tipped, about 1.5 inches long, and maybe an 1/8th of inch round, with two wires (in/out) , but that was long ago. Any hints as to the name of these devices and where to find them would be greatly appreciated. Doug.
Welcome to Bit-Tech! Its not quite as simple as that i'm afraid. The little devices you saw are called Thermistors, there resistance changes with temperature so they are sensors and not switches, you'll need to put one in a basic transistor circuit if you want to use it as a switch for a fan. For more info on Thermistors and Transistors check my guide http://forums.bit-tech.net/showthread.php?s=&threadid=27158
Actually, they do make the switches he is describing, but they are very likely for a much higher temperature than is useful in a computer case.
As Viridius says, common thermostat switches are usually for highish temperatures, and you'll find them on your car or washing machine for high temperature trips. However, Rapid do some that switch down to 20°C, check out the Sensor section of their catalogue, available here. They go by the name of Auto-reset thermal switches and you should find them in the US. Snag is they're fairly bulky, fixed value, and also a wide range, switching on at say 40°C and back off at 25°C. A thermistor and comparator switch has a much smaller sensor and can be set to switch at any temperature, or you can go the whole hog and build a thermal controller that varies fan speed smoothly with temperature for little more trouble. If bulk is no problem, a central-heating room thermostat would switch a fan, bit ghetto though
Thanks for the help. As an update, there are thermal switches that are very small, and can be easily mounted next to sources of heat with a simple plastic ring clip or wire tie. They usually have glass or aluminum covered probe tips, can be normally open or normally closed, and trigger in the range from 20 to 150 degrees, and are designed for low current applications. Some are reed type switches, but there are several varieties. I much prefer the simplicity of and on/off switch over a thermister when an application calls for one. I found a fellow on the net that has them, but I haven't found a retail source for them yet (he's holding that info close to the vest . I have a sample coming in from a company in India as well. The final application will be a simple switch to pass 5v to an 80mm (ZALMAN) fan when temps rise to 35 degrees, and off again when temps are a bit lower (10%?) than that. Quiet cooling only when you need it. Doug.
