Adding a brain to a Kiln.

JimDawson said:
When working with 240V it is my preference to switch both sides of the line. That way the load, in this case the heating element, is completely de-energized, rather than still being electrically hot relative to ground. It would take 2 solid state relays to create a double pole relay to do the same thing. Also with a SSR there is always some leakage current, not much, but they really never turn off 100% thus could be a safety hazard under some conditions. An electro-mechanical relay is better in this regard, not 100% fool proof, but better.
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I always want a seperate two-pole mechanical switch or contactor upstream of and independent of the controller. Given that I have no problem with the controller switching only one line.
 
I like the sound of the relay that switches all lines for safety. I don't really feel comfortable reaching in the kiln with any power of any kind though. I'm new to this, but I think I can live without reaching in there live. Is there good reason to do so? If not, I can probably be happy shutting it all off before getting in there.
 
LEEQ said:
I like the sound of the relay that switches all lines for safety. I don't really feel comfortable reaching in the kiln with any power of any kind though. I'm new to this, but I think I can live without reaching in there live. Is there good reason to do so? If not, I can probably be happy shutting it all off before getting in there.
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You will also want a service disconnect switch to be able to manually kill all power to the kiln, or just a range plug would work also. Last I looked the big box hardware stores carry 30 and 60 amp disconnects for hot tubs and air conditioners.
 
LEEQ said:
I like the sound of the relay that switches all lines for safety. I don't really feel comfortable reaching in the kiln with any power of any kind though. I'm new to this, but I think I can live without reaching in there live. Is there good reason to do so? If not, I can probably be happy shutting it all off before getting in there.
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You could include a limit switch operated by the door or lid on the kiln. It would be wired in series with the controller output and the contactor or other device would drop out (turn the power off) when opening the kiln.
 
uncle harry said:
You could include a limit switch operated by the door or lid on the kiln. It would be wired in series with the controller output and the contactor or other device would drop out (turn the power off) when opening the kiln.
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I like the micro switch idea, but don't know why I would need to be in the kiln during operation. I would think that interrupting power during a cycle would be counter productive. I am hoping to construct a very simple control, adding such luxuries later if I decide they would be important additions.
 
LEEQ said:
I like the micro switch idea, but don't know why I would need to be in the kiln during operation. I would think that interrupting power during a cycle would be counter productive. I am hoping to construct a very simple control, adding such luxuries later if I decide they would be important additions.
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The opening of the kiln during a cycle could compromise the process in some instances. I had a "brilliant" lab assistant who opened a hot kiln some 20 years ago & in so doing blew a 2-day experiment & about a $ 1000.00 invested.

The limit switch would insure that any exposed heater coils are not energized when the kiln is opened when cold.
 
I was thinking of using a big switch to kill all power to the unit if it is hard wired, kind of like a disconnect. If not, just pull the plug. After a cycle is complete, the unit doesn't need power until I use it again. I probably won't use it more than a half dozen times a year, so Flintstone simple circuits and a need for a safety protocol won't bother me. Adding the lid switch later if I decide to shouldn't be to big a deal.
 
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