Hey Y'all,

I'm pretty new to this stuff but am currently working on a project. I think I have actually figured out all the harder stuff but now need to find a way to build a cheap, simple and small thermostat or thermal switch. The accuracy of the temperature is not all that important. The project box contains a Raspberry Pi and a few other boards and 4 SSRs so I expect it will get pretty warm. I am converting some of the power to 5V @3A so plan to use this for the fan. I would like to be able to run power straight through some sort of thermal switch that will kick the fan on around 90-110F or so and just run it until its below that.

Does anyone have any recommendations for thermal switch, thermistor/potentiometer or small relay setup? Again, the emphasis is on small and cheap and I'm not too concerned with absolute accuracy. Just need it to run when warm and not when cool.

 

Oh, and, thanks in advance!

 

Not sure if this helps but I have these laying around I could use if I need to.
1 5V DC relay
1 50K Potentiometer
1 non-descriptive temperature sensor
1 S8050 NPN Transistor
1 2N7000 MOSFET Transistor

 

http://klixon.com/klixon/thermostats-thermostat.htm

Do some interweb searching. There are hundreds of temperature sensors by dozens of manufacturers.

 

http://klixon.com/klixon/thermostats-thermostat.htm

Do some interweb searching. There are hundreds of temperature sensors by dozens of manufacturers.

There are quite a few temp sensors there for sure. Some quite expensive. Does the voltage of my source and load not matter? I couldn't find any there for 5V. I would like to continue using this as a teaching lesson if possible as well.

Ive come across this which looks like it would work great but says it 12v so I wasn't sure it would work and I couldn't find a 5V one.

http://www.amazon.com/Single-Channel-Thermal-Control-Sensor-Temperature/dp/B00VFD08RQ

 

You run into trouble trying to use a 120V sensor for a 5 volt application because the 5 volts will not pierce the oxide layer. I don't think you're going to find anything rated for 5 volts, so use 12 volts rated. If you absolutely have to make it reliable for years and years, avoid all moving parts by building a solid state thermostat.

 

There are quite a few temp sensors there for sure. Some quite expensive. Does the voltage of my source and load not matter? I couldn't find any there for 5V. I would like to continue using this as a teaching lesson if possible as well.

Ive come across this which looks like it would work great but says it 12v so I wasn't sure it would work and I couldn't find a 5V one.

http://www.amazon.com/Single-Channel-Thermal-Control-Sensor-Temperature/dp/B00VFD08RQ

I think it needs 12 volts for the relay, but if you check out ebay you can probably find some like #12 posted pretty cheap.
http://www.ebay.com/itm/Two-2-Therm...Your-Choice-/331245272819?hash=item4d1fc1bef3

 

Do you have a spare AD input channel on the Pi?

If so, a thermistor and a resistor to create a temperature-dependant voltage-divider tied to the AD input, a little code, an output port-pin, and you are done.

Here are a few of them to consider.

 

Have a look for velleman kits mk138


http://www.velleman.co.uk/contents/en-uk/p64_mk138.html

 

Since accuracy is not important, why not just use an actual thermal switch?

 

Thanks for everyones input!

I think the thermal switch will probably be the simplest option. Something like what @ronv mentioned.
http://www.ebay.com/itm/Two-2-Therm...Your-Choice-/331245272819?hash=item4d1fc1bef3

Basically just a normal open switch that will work with any voltage and close the circuit above a certain temperature.

I also came across this:
http://www.radiolocman.com/shem/schematics.html?di=47949

I have all of those parts so maybe make one of those.

Seriously appreciate all the help!