2024 · great-grandmother's china kiln
Ceramic kiln retrofit
High-school pottery turned into a basement studio. This is my great-grandmother's Paragon china kiln, upgraded from about 1700°F to 2300°F with new elements, a fume hood, and automated firing. The interesting work is the electrical and safety stack — not a from-scratch PID written for 240 V.
Garage testing phase — barrier, extinguisher, and the controller UI on a tablet.
How the controller behaves
Firing curve
A sped-up model of what the LAN dashboard is doing: a schedule of setpoints, a thermocouple that lags the brick, and SSR duty from the error. Over-temp trips abort. This canvas is original to the site — the Pi runs jbruce12000/kiln-controller.
Hardware I specified
- Replacement coils: 2500 W, 240 V, channel 102 × 0.5 × 0.5 in, target ~23 Ω, surface loading ≤ 15 W/in², 1300°C application.
- Basement install with a fume hood interlocked to element power (double-throw — both legs of the coil disabled unless the vent is on).
- SSR on a heatsink with a cooling fan in a wall-mounted box, Unistrut on concrete.
- Cinder-block barrier and metal gate, thermal fuses in the original knob enclosure, GFCI breaker, fire blanket and extinguisher in reach.
Firing controller I commissioned
On a kiln this size, writing a new control loop would have been the wrong risk. I put a proven open-source stack on a Raspberry Pi with a static LAN address and wrapped it in the electrical and mechanical safety above. The project is jbruce12000/kiln-controller (GPL). I did not author that PID or its web UI; I selected it, hosted it, and made the plant it talks to safe.
What that stack actually does on this kiln:
- GPIO 23 → zero-cross SSR; MAX31855 K-type thermocouple; ~2 s duty window.
- PID with a control window and anti-windup; schedule holds until the kiln catches the setpoint.
- Abort on over-temp or lost thermocouple; optional brownout resume.
- LAN web UI (sensor vs target, cost estimate, schedule editor) — the tablet on the stand in the photos.
Thermodynamics of element durability, PID in a noisy thermal plant, and redundancy: a software abort is not a substitute for fuses, GFCI, and a blanket on the wall.
Build photos
