Turn on 120V Box Fan on temperature rise?

[MikeMl]

I can dream up all kinds of elaborate thermostats using thermistors or LM34/35 and an opamp driving a small relay to turn on a fan in a power supply I am building.

However, it is all getting too complicated. Anybody have any suggestions for where to get a simple make-on-rise thermostatic switch. I thought I had some in the junk box, but they turned out to be normally closed, and they open on temp rise. Also, they trip at 80C, and I would like about 50C.

 

[Sceadwian]

Check digikey, I doubt you'll find a single device that will switch full load current, but you should be able to find a NO thermal switch that can trip a 120V relay low current relay to drive the real load. If you search for a while and come up blank let us know, me or someone else might have better luck hunting through their search engine, which can be quiet blind.

 

[Sceadwian]

oh yeah, almost forgot to ask. What's the current? By box fan I'm asuming you mean this generic consumer models, so just a few amps?

 

[MikeMl]

About 1/4A at 120Vac. Its just a 8"x8" Muffin Fan.

 

[Hero999]

Replace R2 with a thermistor and (assuming the thermistor NTC) is swap the positions of R1 and R2.

 

[nathan]

This is a rather late reply, but I found the thread googling and thought it would be useful for someone else. I have a water cooler/warmer which has a single component 120V temperature switch to control the hot water heater, so I knew the part existed I just wanted to find the appropriate part. A CanTherm B12 series part should do the trick. They have several models that switch at different temperatures and cost just under $10 from Digikey.

 

[Reloadron]

Maybe something **broken link removed** Small disk type thermostats that close on rise and handle more current than you need to worry about for about 13 bucks. I linked to Selco as a manufacturer and am sure besides Allied they are distributed by other parts houses. Close at 140 F and open at 110 F. or a collection of others.

<EDIT> Nevermind as I just caught the date. I would guess it is running by now and sorry for a necro post. </EDIT>

Ron