My first DIY kiln controller

red bowl
I learned how to fuse glass in a John C. Campbell course (link here) taught by Beverly Fuller (she’s excellent!). It was a great experience, during which Beverly emphasized the importance of understanding the firing schedule, and how to work with both built-in kiln controllers and the stand-alone digital controllers that some of the older studio kilns were plugged into.

For those not familiar with glass fusing, it differs from ceramics firing in that glass requires a multi-step firing schedule, with controlled heating (often at several different rates for different steps in the process) and carefully controlled cooling to relieve the stress introduced in the fusing.

When I got home from the course I was faced with a choice: buy a glass fusing kiln with a digital controller, or build a digital controller to use with the manual kiln I had inherited from my Grandmother. Grandma’s kiln was an 11 inch Paragon hexagon which she had used for several years to fire her painted china. After finding several instructional pages on the web I decided to build my own controller to use with Grandma’s kiln. The kiln was probably 20 years old when I inherited it, and it had three power settings (low/medium/high) and was controlled by a Paragon “kiln sitter”. The kiln sitter was a mechanical device that you armed by lifting a trigger, placing a pyrometric cone of the proper rating in between two contacts, and then releasing the trigger. The cone held the trigger open, allowing current to flow to the kiln. When the target temperature was reached the cone slumped, allowing the trigger to close and killing power to the kiln.

I opened the switch box, disconnected the wiring, removed the kiln sitter mechanism, and reconnected the wires to bypass the unit. At that point “all” I needed was to build a digital controller to plug it into. I could then set the kiln on high and let the controller turn the power on and off.

I found several tips on the web, and a clear set of instructions written by John Tobler. I couldn’t find the Fuji controller John used in his build, but I found another manufactured by Auber Instruments (a Georgia company!) that seemed perfect for my needs. After quite a bit of study and planning I bought some components locally, and ordered the rest. I chose the Auber SYL-2342P, which is a 1/16 DIN ramp/soak controller that can hold up to 30 program steps. At the time I wasn’t sure how to work with solid state relays and heatsinks, (they’re easy, I just wasn’t sure how to mount the heatsink correctly and thought I could save money) so I bought the relay output model and a simple SPDT relay (Zettler AZ2280-1C-120AF). I also bought an enclosure, toggle switch, LED power indicator lamp and a NEMA 5-15R panel mount socket.

I struggled a bit with the wiring diagram, but finally came up with a plan that worked. For those unfamiliar with electronics (I’m a rank beginner), the controller turns current to the relay on and off based on it’s programming and the thermocouple input, and the relay then switches the 110V 15A circuit on and off. Using the relay allows the switching of the heavy current load (the kiln) with the low amperage circuitry of the controller.

The enclosure I bought already had an opening for the 1/16 DIN controller, and I drilled the other holes needed with a step bit (essential for holes in sheet metal).

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After about an hour of drilling and fiddling around I finally got everything mounted in the box and ran all the wiring. I used 14GA wire for the circuit that would carry the load of the kiln, and 18GA stranded wire for all the other connections. Once everything was hooked up I crossed my fingers, plugged it in, and flipped the power switch. The controller display lit up, and I realized a moment later that I didn’t need the LED power indicator lamp, since the controller display is only lit when the power is on. Oh well.

I then plugged in the kiln (with it’s power control turned to high), and slipped the thermocouple into the kiln peep hole, padded with a bit of fiberfrax. I programmed the controller to ramp from room temp (70F) to 500F over 30 min. After setting the controller to “run” the relay clicked and the kiln came on, stayed on for a minute or so, and cycled back off. No sparks, no smoke, good. It kept cycling on and off, with the temperature reading rising, and after 30 min it was within a degree or two of 500. Success!

A few photos of this build:

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