Kiln Question

[Leothwyn]

Hi,
I had an issue with my kiln yesterday, and am wondering if anyone can shed any light on what might have happened.
I was on the torch when the lights started flickering and went dim. As soon as I realized that it was a brown out I shut off the kiln and ran to shut off other things that would be affected. The power went completely out for a while, then came back on a couple of hours later. I went into the glass studio and could immediately see glowing orange around the edges of the kiln door. The kiln was switched off, and the digital display was dark, but the kiln was running! I unplugged it. I now know that I should have done that from the start, but I really thought that the toggle switch in the off position meant that no power was getting past the switch. The kiln (AIM digital) has an old fashioned manual toggle switch - up for on, down for off.

So, the work that I had done yesterday (not much luckily) was turned into a pancake. The kiln seems to be working just fine now, and it's holding a steady temperature, but it makes me nervous. I'm worried that something got messed up, and it's going to go crazy again.

EDIT: After working fine for a bit, the kiln has started doing the same thing... heating non stop, whether the switch is on or off. I have to unplug it to turn it off.

EDIT #2, for anyone who might find this to be useful. I've talked to a couple of people who confidently say that I need a new relay. AIM kilns was really helpful on the phone, and I'll get a new relay from them in the next few days.

[PyroChixRock]

Your relay went out! It's never fun but doesn't happen often. It's not hard to change out.

[AxisWolf]

I wonder if those AIMs can take a mercury relay? Those last a very long time.

-J

[PyroChixRock]

I've heard they can, but there is some converting of some sort we have to do. Doug was talking to me about it recently. I'll see if I can get him in here.

[Greymatter Glass]

I wonder if those AIMs can take a mercury relay? Those last a very long time.

-J

Aim kilns, like any other kiln, can certainly be run on a mercury relay but it really depends on the controller.

For decades AIM really only sold the Fuji PXR3 and it's various predecessors. Now they sell several controllers and so the information you'd need is what's called the "coil voltage"

For the PXR3 and it's ilk (Fuji) that is usually 120vac, but they can be configured at the factory for other voltages so you really just have to know what you need.

You'd also need to know the switch voltage (you need something rated for main voltage AC, typically this will show as 300vac or 600vac on the relay) and current. Most kilns will typically need a 30A relay but some smaller kilns you can get away with a 20A - you don't want significantly more than your kiln is rated for, but typically want a 10-15% cushion if the closest size it within a few amps go one size up.

You can usually get all this info from the relay already in your kiln, there will be a data panel on the relay with this info, but over time this can wear away or if the relay fails burn off. If in any doubt, call the manufacturer.

Now, a mercury relay is not just a drop in part either - you may need to modify your kiln to make it work. While a normal mechanical relay will generally work in any position a mercury relay has a gravity component to it and has to be oriented right side up. They also tend to be more temperature sensitive than a mechanical relay, so they're often placed in a ventilated shell on the exterior of the kiln rather than under the kiln. Many people have made stand alone boxes mounted on the wall next to the kiln with heavy power cables from the relay to the kiln.

But all that to say, yes it can be done.

Another option, what I run, is an SSR (Solid State Relay). Some controllers can make use of PWM mode and cycle your kiln 120 times a second (or more) - the result is your elements run cooler and maintain a much more stable temperature. Even without PWM a SSR can be more reliable than a mechanical relay. They have no moving parts and ir properly sized can last decades in use. They do require a cooling fan and a bit more work to properly spec the part depending on what features you're trying to make use of. If you're going to modify a kiln for a mercury relay an SSR is an equally viable option and if your controller supports PWM it's worth it 100%.

My kiln runs on an SSR (old Living Glass Works Antares) on a Digitry GB-8 board. The PWM keeps my elements barely glowing, runs stable and have for about 15 years. I did replace the stock SSR with a high quality Omron relay because the stock relay they used were cheap garbage.

Also, I think this is my first new post here in like 4 or 5 years, glad to see the forum is still alive and kicking!