How often do you change relays on your kilns, and over-temp protection questions

[Piedmont Pottery]

I had my first ever relay stuck closed on one of the kilns this week.  Fortunately I was here when it happened.  New relays arrived today and I will be installing them tomorrow.  I had been planning on ordering new relays as I was up to about 250 firings on the current set.  So a couple of questions for the group:  How often do you change the relays on your kilns, and are there any reasonably priced over-temp protection devices that I can instal inline with my controller?  The kiln in question is an L&L eFL2635, which is an 80 Amp kiln.  As far as I know, Dawson kiln setters aren't able to handle that much current.  I'm using a Genesis controller, but the relays are pretty much a separate issue from the controller.  I am concerned because I am often firing while I'm not here, and concerned about the potential for destroying a load of pieces, especially student pieces.  I know it's not a great idea to fire while not present in theory, but I've never actually encountered this until now., after decades of firing.  I have no problem with changing the relays more frequently, but an overtemp cut-off would be a nice to have feature.  I know that there's an option from L&L, but it's about $1k, and I was looking for less costly suggestions, like maybe a temperature controlled circuit breaker, although I've not yet found one that will accept type K or S thermocouple probes.

[neilestrick]

If one relay sticks, the kiln will not over-fire. It will simply cool slowly and get stuck at around 1800F. The odds of two relays getting stuck is very, very small. I've never seen it happen. If you really want some sort of over-firing protection, you'd need to install a master relay that can handle the entire amperage of the kiln, or a second relay in line with each of the existing relays. There may or may not be space in the kiln for either of those options, though. You could rig up an external box to house it. The safety relay(s) would be controlled by Output 4 on the controller.

[Piedmont Pottery]

28 minutes ago, neilestrick said:

If one relay sticks, the kiln will not over-fire. It will simply cool slowly and get stuck at around 1800F. The odds of two relays getting stuck is very, very small. I've never seen it happen. If you really want some sort of over-firing protection, you'd need to install a master relay that can handle the entire amperage of the kiln, or a second relay in line with each of the existing relays. There may or may not be space in the kiln for either of those options, though. You could rig up an external box to house it. The safety relay(s) would be controlled by Output 4 on the controller.

Thanks, Neil.  I think I can live with a risk of holding at 1800.  I may look into the master relay idea, though.  Any rule of thumb about how often to replace relays?

[neilestrick]

21 minutes ago, Piedmont Pottery said:

Thanks, Neil.  I think I can live with a risk of holding at 1800.  I may look into the master relay idea, though.  Any rule of thumb about how often to replace relays?

It really depends. To stay 99% safe, do them every 200 firings, or even every time you change elements. They're pretty cheap if you source them online. 250-ish firings seems to be a pretty common lifespan, although I've had them last as long as 700 firings. It all depends on how cool they stay. In my L&L DaVinci I don't think I ever replaced the small relays (about 900 firings), but they weren't carrying any real current- just switching the big relays- and they were in a detached control box, so they never got hot. Mounted on a big kiln and pulling a lot of amperage they're going to run hotter and not last as long.

[neilestrick]

1 hour ago, neilestrick said:

If one relay sticks, the kiln will not over-fire. It will simply cool slowly and get stuck at around 1800F.

To be clear to everyone out there: If you have a two section kiln and are using low fire glazes, if one relay sticks it is theoretically possible fore that section of the kiln to over-fire a little bit depending on how you loaded it and how powerful the kiln is. I've never seen a 3 section kiln over-fire from one section staying on. No kiln system is 100% fail-safe, so you always want to check it to make sure it has turned off properly.

[Min]

3 hours ago, Piedmont Pottery said:

I know it's not a great idea to fire while not present in theory, but I've never actually encountered this until now., after decades of firing.  I have no problem with changing the relays more frequently, but an overtemp cut-off would be a nice to have feature.

Yeah, in a perfect world, but if not then a baby monitor with the camera facing the controller might be something to give a little peace of mind.

[cadenrank]

33 minutes ago, Min said:

Yeah, in a perfect world, but if not then a baby monitor with the camera facing the controller might be something to give a little peace of mind.

I have an old smart phone that has a cracked screen that I don't use anymore, and I plug it in on a charger, and use an app called Alfred to monitor both my digital and manual kilns through the old smart phone's camera. 

Of course, baby monitors are relatively cheap too, but I already had the old phone, and the app is free and I can view it from anywhere, so it's a good option if you meet the criteria of already having an old spare phone. 

[Bill Kielb]

On 2/11/2022 at 2:28 PM, Piedmont Pottery said:

I may look into the master relay idea, though

I think the easiest economical way to do this with a very very high degree of reliability is to add that same 12v type relay in series with the present but drive the new safety relays from the safety output of the controller. So no need for a separate temperature device as the controller has this built in and the safety relays last forever because they only cycle on once at kiln startup and remain on until shutdown or controller error which ought to mean,  tens to hundreds of thousands of cycles before failure. Basically the life of the kiln. The cost: add three relays and some wiring. Also maybe enable the safety output of your control.