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Build Your Own Temperature Controller for Yogurt in the Crock Pot

A temperature controller is a very handy device on the homestead. We use them to control our heating system, hot water heater, crock pot (for yogurt), greenhouse fan, and maybe other things that I have forgotten. They are easy to make and can be programmed for heating or cooling. I have used Honeywell brand thermostats for these, but my favorite is the Ranco ETC. You can buy these on ebay for around $50 - search for Ranco ETC.

NOTE: If you attempt this project, you assume all risks and rewards of both the electrical hazard and and control hazards that may occur. In other words - don't come running to us if you fry yourself or your aquarium fish building or using this controller! On the other hand if you solve one of the world's great problems with one of these - we aren't going to ask you for anything either!

You will need a few parts:

1. the controller - Ranco ETC 111000-000 (search ebay)
2. Short extension cord (you will use both ends - available at Lowes or Home Depot)
3. Strain relief cable connector (1/.2" knockout, available at Lowes or Home Depot)
4. Yellow wire nut (or any one that will fit - available at Lowes or Home Depot)

 1. First, cut the cord ends , leaving 10" to 18" ends.

 2. Strip the cord sheath about 4" and strip each wire end.  Cut a 4" piece of black wire from the left over cord and strip both ends of it.

3. Remove the 4 screws on the controller and pull it apart. Lift the cardboard wiring protectors out of the way.

4. Remove nut from strain relief. Push the strain relief through the bottom knockout hole on the controller. Run the nut from the strain relief over the end inside the box and secure it by screwing it tight.

5. Push the cords together into the controller. Leave some slack for working room.

Here's how to think about the wiring: The prong end is supplying power to the controller through the upper terminals. The plug end is receiving the same white and green wires through the terminal and wire nut. The black wire is "switched" on and off by the lower terminals.

3. Wire the controller as shown by twisting the neutrals together and putting them in the upper right terminal. Twist a short piece of extra black to the prong side and insert them both in the upper middle slot. Run the output (plug side) black to the middle bottom. Run the short piece from the middle upper to the right hand lower terminal. Finally twist the green (grounds) together with a wire nut. Tighten the screws on the strain relief. Tighten all terminal screws and tug them gently to make sure the wires won't slip out.

6. Screw the controller back together and you are ready to program it.

7. Plug the controller in. It should come on and display the current probe temperature. You scroll through the simple menus with the SET button. The arrows change the values and you press SET to make the changes.

8. The HI is for heating and LO for cooling.. Use the arrows to select and the SET to enter the selection.

9. I use F, you can also use C.

10. The temp differential is set depending on what you are using the controller for. I use 1 degree for yogurt.

11. I use 116F for yogurt (actually Michelle makes the yogurt - I did the controller so she could use the crock pot and not have to store 2 appliances - crock pot and yogurt maker- in our kitchen) 

 8. Here is the set up - plug the controller into the wall and then the crock pot into the plug on the controller. Turn the crock pot on. Drop the temperature probe into the water in the crock pot. The controller will turn the crock pot off and on to maintain whatever temperature you have the controller set for. We use 116F for yogurt.

Simple! and takes about 15 minutes.


  1. Run the nut from the strain relief over the end inside the box and secure it by screwing it tight. Furnace Repair Edmond


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