I have been trying to find a suitable temperature controller for a fan that I need to fit into a housing. Currently the fan is running continuously which is not ideal.

I have looked on the Internet for a circuit diagram for a very basic temperature controller, and to date Have only found rather complicated circuits.

Precision here is not critical, I need to just be able to turn the fan on and off within a reasonable tolerance.

I am basically looking for a circuit diagram or a link to a site where there is a circuit diagram that I can use to build a temperature controller.

 

Are you happy with on/off control or would you like some sort of proportional control?

A Thermistor for temperature measurement would be idea due to the large resistance change with temperature compared to the more common Thermocouple and RTD.

A Schmidt Trigger can then be used to turn the fan on and off. Using a Schmidt Trigger permits enough hysteresis to prevent constant on/off cycling.

The actual selection of resistors for the reference pin on the Schmidt Trigger will depend on what Schmidt Trigger you use and the Thermistor you obtain.

 

Maybe this.

http://forum.allaboutcircuits.com/blog.php?b=532

 

Are you happy with on/off control or would you like some sort of proportional control?

A Thermistor for temperature measurement would be idea due to the large resistance change with temperature compared to the more common Thermocouple and RTD.

A Schmidt Trigger can then be used to turn the fan on and off. Using a Schmidt Trigger permits enough hysteresis to prevent constant on/off cycling.

The actual selection of resistors for the reference pin on the Schmidt Trigger will depend on what Schmidt Trigger you use and the Thermistor you obtain.

An on off control will be ideal. I am basically trying to move hot air out of a housing, so when it gets to hot, then the fan can come on and blow the hot air out the box. When it cools down, then switch the fan off.

 

An on off control will be ideal. I am basically trying to move hot air out of a housing, so when it gets to hot, then the fan can come on and blow the hot air out the box. When it cools down, then switch the fan off.

Just need a bimetal temperature switch.. no other components needed for that..
Just buy one with the desired on temp and done

 

A comparator watching a LM35 thermometer is more complicated but would be the most versatile, allowing adjustment of the target temperature and the amount of hysteresis.

How is the fan powered, is it AC or DC?

 

An on off control will be ideal. I am basically trying to move hot air out of a housing, so when it gets to hot, then the fan can come on and blow the hot air out the box. When it cools down, then switch the fan off.

Another thing to consider in enclosure cooling is the environment it is in, if it is dusty or otherwise contaminated, rather than go with negative pressure, is to place a filter on the fan and bring air in, = positive pressure.
This way the interior stays clean.
Max.

 

Good point. Easier to filter the fan that trying to filter all the places air can get into the box.