AGAIN - Leaving Kiln w/Bartlett 3 Controller

[Tony Smith]

I would agree with the comments that they SHOULD have a breaker on the kiln and I would also add that I still think it is irresponsible that they do not have a redundant overtemp kill circuit. I just priced what I need to do from available off the shelf parts and it will cost just north of $300 to put a reliable overtemp circuit on my 24" Paragon. This is about a $2400 kiln so doing a way over kill job I can do it for about 10% of the cost. I know for a fact you could accomplish this with about $20 to $30 in real manufacturing cost so if you figure things tend to retail for about 4x the bill of material it could be offered to people for around $100. For the price of a commercial kiln this is cheap insurance and I think that a lot of customers would pay this if it were available to them.

BTW, my controller design will have main breakers with 10' of the kiln and on the control panel itself each element will have a separate breaker to allow me to individually turn on and off elements, in addition to a totally separate and redundant overtemp kill circuit.
Phil

Phil,

I believe that the European electrical code requires that the kiln elements disconnect (electrically) when the door is opened or the lid is lifted. Again, this is all part of the safety systems built into the kiln. For the extra $100 to $200 it would be worth it. I have a tendency to leave the lid up on my kiln when it is empty. (No, I don't leave the lid up on the toilet. With three women in my house, there'd be hell to pay.) It would be my luck that the kiln would turn itself on with the lid up and really heat up the place.

Tony

[Phil Hoppes]

Tony,

Actually I'm not talking about a door kill switch I'm talking about an overtemperature runaway kill circuit. Most larger kilns have a door switch (my Paragon has one). The $20 - $30 cost I'm talking about is you could put a VERY simple limit controller using something like a PIC microcontroller with an A/D input, display controller, keypad controller and 5vdc relay controller output all on one device. In kiln production quantities these would probably be a whopping $3-$4 for the controller manufacturer. Throw in a thermocouple and an SSR with a display or feed to the main keypad and display and you are still talking peanuts. This is a VERY cheap circuit to implement. One can run the numbers but the probability of a failure of multiple relay's/thermocouples/etc. is pretty low so having a redundant limit switch to shut things down is really cheap. It would be most effective if the main relays were Mercury displacement type as they only fail off and this overtemp kill was directly in series with the coil control of those merc relays, that way anything that broke further down the line from the coil control is moot.

Phil

[Tony Smith]

Phil,

I was giving the door kill switch as another example of a safety device that would be inexpensive to implement, but isn't even an option from most manufacturers.

I believe tha bartlett controllers have the capability built in to trip another relay (in addition to the audible alarm) that could be set up in a latching configuration to shut down all of the power to the kiln in the event of a runaway. So, for the cost of another non-cycling relay, you could have the protection we're talking about here.

Tony