revchris

teeka had kiln problems earlier this week because the control relay welded itself closed. This causes the kiln to hold temp at 957C, which is hot enough to puddle any glass in the kiln. Fortunately, she hadn't done anything yet when I noticed it. I shut down the main power to the controller, and then I cleaned the contacts with some 400 grit sandpaper, and turned it back on to cool down, with no problems.

Last night, she made more beads, and everything was worked properly. When I got up this morning, I noticed that her shop was at 82F, so I figured she'd left the heater on, and I'd turn it off on my way to work. Then I looked out the window above my computer, where I can see her kiln. It's power light was on continuously (the light comes on when the controller supplies power to the furnace, so it should be blinking), and the kiln was glowing bright orange around the bead door.

At some point during the cool down part of the cycle, after she had gone to bed, the relay welded itself again.

I just ordered a new relay to replace the current one, and I ordered a second relay to wire into the alarm circuit of the controller to act as an overtemperature limiting relay and cut the power when the controller goes above the specified alarm temp. Mechanical relays are only good for about a million cycles. We're going to start replacing the main relay every year as a maintenance item, and I'm going to try to clean the relay contacts every three months to help limit contact resistance.