Water Bath Thermostat

Controls both heating and cooling!

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This project was inspired by Cooking for Geeks author Jeff Potter's quick DIY sous-vide hack. My plan, initially, was to just hack the controller into an enclosure with an A/C outlet, the idea being that you could just plug any heater you wanted into the outlet.

Looking around for cheap temperature controllers, however, I happened across the STC-1000 on eBay for $25. It's not PID, but I was betting it would still be accurate enough for almost any practical purpose. And since the STC-1000 has both heating and cooling functions built-in, the logical next step seemed to be to split a single A/C outlet so that you could plug a heater or a cooler (or both) into it and use it for all kinds of stuff.

The STC-1000 will regulate at any temperature between the freezing and boiling points of water, which opens up potential applications in chemistry, aquaculture, zymurgy, hydroponics, cooking, etc., etc.

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Add Note Edit Step 1 — Prepare sensor jumper cable  ¶ 

  • Cut a 4" length off the end of the STC-1000's bundled temperature sensor cable, and separate and strip the cut wire ends.

  • Remove the ring terminals from the binding posts and bend each at a 90-degree angle using two pairs of pliers, as shown.

  • Twist the stripped wire through the holes on the bent up leg of each ring terminal, forming a strong mechanical bond before soldering.

  • Flux and solder the ring terminals to the ends of the cable.

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Add Note Edit Step 2 — Prepare A/C outlet  ¶ 

  • Break off the "ears" on the outlet mounts with a pair of pliers. They are scored for this purpose.

  • Also break off the metal connecting tabs on the bus bars on the sides of the outlet so that each socket can be controlled separately.

  • Remove the screws from the mounting flanges. They will not be used for this project.

  • "Decora" outlets have additional ears on the mounting flanges for the faceplate screws. Cut these off with large side-cutters and file the cut ends smooth.

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Add Note Edit Step 3 — Apply power connector template  ¶ 

  • Print the PDF template attached to this project onto an adhesive-backed mailing label.

  • Cut out just the power connector template, for now, and peel off the protective backing.

  • Apply the template to one of the two sides of the junction box that is without a mounting ear. Center the template vertically, and align it horizontally with the bottom edge of the box, about 1/4" up.

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Add Note Edit Step 4 — Install C14 power port  ¶ 

  • Drill 3/16" holes aligned to the inside corners of the template. Start by marking the indicated centers of the holes with a sharp punch, then drill starter holes with a 1/16" bit.

  • Rotate the box 90 degrees, as shown, and clamp the mounting ears to the edge of the bench top with the drilled side facing out.

  • Thread the blade of your coping saw through one of the upper two holes. Assemble and tighten the saw.

  • Rotate the saw blade as necessary and cut out each of the four sides of the opening.

  • Test the power connector's fit in the opening, and file the sides as needed to expand it.

  • Once the C14 port fits in the opening, use the mounting holes in its flanges as a template to drill two small holes in the side of the box. Install the C14 port mounting screws and tighten into hex nuts inside the enclosure.

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Add Note Edit Step 5 — Apply panel cutting template  ¶ 

  • Use a pair of scissors to cut around the outside edge of the panel template. Cut to remove the line.

  • Peel off the label backing.

  • Carefully align the template with the lip on the underside of the junction box lid and press it down.

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Add Note Edit Step 6 — Cut panel openings  ¶ 

  • Use a 3/16" bit to drill twelve holes in the lid where indicated on the template.

  • Thread the blade of a coping saw through one of the corner holes and assemble and tighten the saw. Saw as necessary to connect the four corner holes in each panel opening. One of these openings will hold the A/C outlet. The other will hold the STC-1000.

  • Use a file to finish out the edges of the openings you just cut. Smooth out any rough spots and flatten each edge, being careful to keep the corners round. Test the component fit occasionally to figure out when you're done.

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Add Note Edit Step 7 — Install A/C outlet  ¶ 

  • Fit the outlet into the upper opening. From the front side of the panel, insert the two retaining screws.

  • Holding the screws in place, turn the panel assembly over and set it on the bench. Add a split lock washer and a hex nut over each exposed screw end.

  • Tighten the screws with a flat screwdriver while holding the hex nuts with your fingers or a small wrench or socket. Tighten until the split washers are fully compressed, and no further.

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Add Note Edit Step 8 — Install binding posts  ¶ 

  • Remove all nuts and washers from the binding posts. Each post should have two hex nuts and two insulating washers. The washers are not needed for this project because the enclosure is plastic.

  • Insert the binding posts into the mounting holes from the front of the panel as shown.

  • Secure each binding post with a single hex nut tightened against the back side of the panel. A small socket may be helpful for this operation, as in the following step.

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