I have Googled the net for an hour now looking for a source of one or two surface-mount thermal snap switches to no avail. I'm looking for a cheap (operative word--cheap)unit the will close on drop to about 30F and open somewhere above 30F. Lots of Airpax and Honeywell stuff out there, but I'm interested in building a freeze-protection system and not to instrument the space shuttle.
Can anyone out there point me to a small-quantity source?
TIA
Terry--WB4FXD Edenton, NC
There aren't many snap switches that operate at that temperature. It is difficult to get consistent operation below ambient temperature. Most of the ones you will find operate at much higher temperatures and are designed to provide high temperature limit.
There are some filled bulb type thermostats known as "cold controls". They are used in icemakers, refrigerators, etc. for the exact type of thing you are doing. The bulb is a small cappilary tube that you can mount to a surface or hang in the air. I think Grainger carries some as replacement parts. They are relatively cheap.
Ben Miller
=>Terry wrote: =>> I have Googled the net for an hour now looking for a source of one or =>> two surface-mount thermal snap switches to no avail. I'm looking for a =>> cheap (operative word--cheap)unit the will close on drop to about
30F =>> and open somewhere above 30F. Lots of Airpax and Honeywell stuff out =>> there, but I'm interested in building a freeze-protection system and =>> not to instrument the space shuttle. =>>=>> Can anyone out there point me to a small-quantity source?
=>There aren't many snap switches that operate at that temperature. It is =>difficult to get consistent operation below ambient temperature. Most of the =>ones you will find operate at much higher temperatures and are designed to =>provide high temperature limit. =>
=>There are some filled bulb type thermostats known as "cold controls". They =>are used in icemakers, refrigerators, etc. for the exact type of thing you =>are doing. The bulb is a small cappilary tube that you can mount to a =>surface or hang in the air. I think Grainger carries some as replacement =>parts. They are relatively cheap.
Thanks, Ben. I guess that's why I'm having the problem. I'll try new parameters for a search per your suggestions and see what comes back.
Cheers-- Terry--WB4FXD Edenton, NC
=>There aren't many snap switches that operate at that temperature. It is =>difficult to get consistent operation below ambient temperature. Most of the =>ones you will find operate at much higher temperatures and are designed to =>provide high temperature limit. =>
=>There are some filled bulb type thermostats known as "cold controls". They =>are used in icemakers, refrigerators, etc. for the exact type of thing you =>are doing. The bulb is a small cappilary tube that you can mount to a =>surface or hang in the air. < snip >
Benn--Found just the part:
Thanks again--
Terry--WB4FXD Edenton, NC
Terry Glad you found it. A few pointers: The control responds to the coldest temperature anywhere along the capillary tubing. If you are measuring a surface temperature, attach at least 6" of the tubing to the surface, and be sure the rest of the tubing, and the control itself, stays at least slightly warmer. Have fun.
Ben Miller
I think these are commonly used in refrigerators and perhaps heat pumps to terminate the defrost cycle.
Don Young
Terry used his keyboard to write :
You need a simple variable thermostat. a Danfoss UT-72 will do the job. I have used lots of them and they are very reliable.
Any HVAC supply that stock danfoss will have them.
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