Previously a glass blowing apprentice, I have been fusing for a short time. Up until this point I have had only small problems that I 've been able to figure out until tonight.
I went to my studio and turned on the kiln to fuse two small plates.
Schedule:
400 dph to 1250
200 dph to 1350 ( I was firepolishing the edges too)
hold 10 min
full pwr to 960 hold 30 minutes
100 dph to 700
I have used this schedule before and it has worked fine UNTIL tonight.
After holding at 1350 the temp began to climb. I watched in horror. I vented the kiln. And it just kept going up. I vented again...a few times.
It wouldn't stop. I reviewed my schedule, it was programmed right. I read the controller manual and it offered NO help.(Sentry Express 3.0 on a Skutt 24') And then I watched as the pieces shrunk up like the shrinky dink toys I made when I was young. I knew this would happen but had never seen it happen. It was like the kiln god was posessed and was sucking the precious life out of the pieces. What do you think happened? Should I call a priest, get some holy water ? The power had gone off in the studio earlier in the day. Could that have affected the controller?
even though i am still in the process of building my kiln, my local kiln heating expert told me this sort of thing happens. the controller just loses itself. somehow. to stop this from happening to my kiln i've been told to fit 2 controllers. 1 main controller and the second is a "over tempreture" controller. if the tempreture goes over a said limit, the second one cuts in effectivly overiding the first. it is programed to basically turn it off stopping a potential melt down. i am running 2 shinko's one big one and then the smaller one. has any one else used this method? my kiln is quite big, it is a 24kw. 3 phase.
hi jennifer, i do not understand the full power to 960 part of your schedule. but when in doubt, pull the plug. works for computers too! lol. gotta love those opposable thumbs. rosanna
Rosanna, I think she probably meant AFAP (as fast as possible) to 960.
But getting back to Jennifer's problem, it soulds like your relay contacts fused closed. It does happen, not often, but it does. Like Rosanna said, pull the plug or throw the circuit breaker (which is a better idea). A runaway kiln can be a mess to clean up. As John said, you can set up a second controller to stop runaways, or you can (depending on your controller) wire in a second relay that will trip at the alarm temperature and shut off all the power to the kiln.
With that said, it's rarely the controller that goes whacky. It's either a programming error or a relay. You might consider replacing the existing relay with one of a higher current rating/life cycle... especially if your kiln hasn't been used a lot.
Tony
Last edited by Tony Smith on Thu May 08, 2003 4:13 pm, edited 1 time in total.
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
John wrote:even though i am still in the process of building my kiln, my local kiln heating expert told me this sort of thing happens. the controller just loses itself. somehow. to stop this from happening to my kiln i've been told to fit 2 controllers. 1 main controller and the second is a "over tempreture" controller. if the tempreture goes over a said limit, the second one cuts in effectivly overiding the first. it is programed to basically turn it off stopping a potential melt down. i am running 2 shinko's one big one and then the smaller one. has any one else used this method? my kiln is quite big, it is a 24kw. 3 phase.
My friend Jack Bowman is building his own kiln currently and is using the very kind of over-ride system you are talking about. Or at least I think that's what he is talking about with me. If I understand correctly, it's like a fail safe switch that if the kiln temp rises above a set temp it shuts everything down. Once he described this to me and told me how inexpensive adding this particular switch would be, it made me wonder why that isn't a standard relay on all controllers...
You can find his contact info for private messaging in the member list if you want to get in touch with him about it.
Thanks Tony! You were right, the relay is broken. I called the manufacturer and they are sending a new one as it is still under warrenty.
I too, am wondering if this is such a common problem then why don't they install the overide as a standard on all kilns.
Thanks to everyone for their input.
They don't because it costs money. And with any company, the bottom line is very important. Many controllers have safety features and relay drivers built into them, but they are not used because of the effect on the bottom line. It's really shortsighted since most glass artists value their studios and homes and wouldn't mind payuing a few extra dollars for the additional safety features.
Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
Jennifer wrote:Previously a glass blowing apprentice, I have been fusing for a short time. Up until this point I have had only small problems that I 've been able to figure out until tonight.
I went to my studio and turned on the kiln to fuse two small plates.
Schedule:
400 dph to 1250
200 dph to 1350 ( I was firepolishing the edges too)
hold 10 min
full pwr to 960 hold 30 minutes
100 dph to 700
I have used this schedule before and it has worked fine UNTIL tonight.
After holding at 1350 the temp began to climb. I watched in horror. I vented the kiln. And it just kept going up. I vented again...a few times.
It wouldn't stop. I reviewed my schedule, it was programmed right. I read the controller manual and it offered NO help.(Sentry Express 3.0 on a Skutt 24') And then I watched as the pieces shrunk up like the shrinky dink toys I made when I was young. I knew this would happen but had never seen it happen. It was like the kiln god was posessed and was sucking the precious life out of the pieces. What do you think happened? Should I call a priest, get some holy water ? The power had gone off in the studio earlier in the day. Could that have affected the controller?
One solution is 2 have a heat fuze which is wired in so if U get 2 hot it will burn out cutting the power
But the one I got works from the relay
But I think U can get mains ones which work B4 the relay
Relays do fail but not often
I think U got a faulty one
A few years back the was a good disacudssion on this will B in the achives
As one who has extra relays on hand (guess who's been burned), I thought I would forward the information that you can find them at Grainger's... I'm switching out to mercury relays in the bigger kiln next month.
I just went to Jack Fielder's class on kiln building last month. (Good class, I recommend it to those interested.) A couple of things I would mention here. 1) If you are going to spend $1000 or a lot more on a kiln, invest in mercury displacement relays. They typically come in two sizes, 30A and 60A. This type of realy does not have contact surfaces that can fuse. Both mechanical and solid state relays fail in the closed position so when they do fail you will have a runaway kiln. For overtemp protection the best thing to do is put a kilnsitter in series with the relay control connection. Put a cone in there that will be 50 to 100 degrees hotter that what you would ever want your kiln to go. If the controller fails or relay's fail once the temp gets to the cone temp the kilnsitter will kick in and shut the kiln down. Remember, even with mercury displacement relays you can still have a run away kiln as the their are relays, mechanical or solid state, on the controller board too and they could fail.
It really ticks me off that this is the most common failure point probably next to element failures on kilns and for cost of a second cheap relay on the controller board and a little more expensive relay for the main elements that the manufacturers don't put this in. The lack of an overtemp shutdown is inexcusable. But I digress.........this is one of may reasons why every kiln I get from now on, I'm going to make myself.
