I am working on a thermostat project and I have passive bimetal temperature switches built in in case of electronics failure.

Right now I have these types of switches ( http://m.ebay.com/itm/KSD301-Temperature-Switch-Thermostat-65-C-NC-Normal-Close-KSD-301/251120845289?_trksid=p2053742.c100465.m3226&_trkparms=aid=555014&algo=PL.DEFAULT&ao=1&asc=20150608111723&meid=b62a2786bce948e4aed6ac45b9a5ef43&pid=100465&rk=1&rkt=1& ) which are quite bulky. Can any one point me to a smaller kind?

 

Smaller? Compared to what dimensions? Do you really think I will keep digging the internetz for dimensions when you could have told me what they are from the start?

 

These are small but they are not cheap.

 

Those are the standard bimetal kind. There are some wax based ones which are a lot smaller but they are one time devices. If they overheat they break the circuit permanently and must be replaced.

 

Smaller? Compared to what dimensions? Do you really think I will keep digging the internetz for dimensions when you could have told me what they are from the start?

24mm(.945in)x 20mm(.787in)

 

Hum... this doesn't look promising. In the case that a smaller one can't be found, does anyone have any other interesting ideas for replacing these switches with something else? They need to be in the design as the relays are switching, so the heat or ac could get stuck on.

 

@Kalli Vahrenkamp
Are you related to Jeffery or just happen to look like him?

 

blah, just signed in with my wifes google...

 

You could certainly use a thermistor and a circuit to control a relay.
Would that work?

 

blah, just signed in with my wifes google...

Well then a warm welcome to AAC to you and Kalli and the baby.

 

You could certainly use a thermistor and a circuit to control a relay.
Would that work?

Right now I have an ESP8266 board switching two relays turning the heat and ac on and off. Between the COM and the HEAT pins I have a bimetal switch that breaks the connection at 35C. I also have a bimetal switch between the COM and the HEAT to turn it on when the temperature reaches 5C. The power on that circuit would be AC 24V. I have no idea how I'd make a circuit to turn that on or off with a therm resistor, though I am open to suggestions.

I did find these ksd9700 switches which are much smaller, but can't find any 5C NC switches.

 

What is the relay coil voltage and is that AC or DC?
A complete schematic of the total system would be very helpful.

 

What is the relay coil voltage and is that AC or DC?
A complete schematic of the total system would be very helpful.

@crustchow
The smaller traces are 3.3V (run from an esp8266 breakout board). The larger traces are the 24VAC circuit for the HVAC system.

 

The relays are double pole double throw. Trying to replace the large switches at the bottom which are bimetal switches.