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Hey all, Finally have a chance to throw up some photos and info about my curing oven. This isn't anything special, function was the priority and specifically energy efficiency and low capital cost. I thought about doing a steel or ali body, but not only does this work out exponentially more expensive and time consuming to build, but it actually has poorer heat transfer properties - meaning it leaches energy. In the end I decided on a timber frame (the front of the frame is aluminium for extra strength and to prevent wear from opening and closing the doors all the time), 16mm MDF as the external structure and 3mm fibreboard as the internal structure. The timber frame provides the 42mm spacing between the internal and external structures, and I filled this space with 'Kingspan' type fibreglass insulation, giving me a total wall thickness of 63mm. Some pictures:      As for the electronic side of things, the element is a 2000W element off ebay and the SSR is your standard AC/DC SSR mounted on a heat sink. There is a 130 degree cut-off switch mounted inside on the roof for safety. I used an Omega CN7800 Series PID controller, and this was the most expensive thing about the entire build. I decided the controller was the important piece of the puzzle, so I splash on a good one and I'm glad I did - it works very very well. The only thing I regret about the PID was that I didn't realise Omega have various models within the CN7800 series; one of which has a built in power supply on the output and one which does not - I bought the one that does not. This required me to wire up an external 9v battery to provide the input voltage to the SSR. Not a big deal in itself, however it does make things a little messier (and I now have a battery that I need to replace every so while), and it did provide a lot of confusion when it came to getting the oven to work. One trap for young players: Don't believe the spec sheet of your SSR when it says it needs a 3-12v input to switch the relay. I originally wired up a 5v phone charger as the power supply, and it took me days of playing around to figure out that although this 5v input was enough to switch the LED light on on the relay, it wasn't actually enough to switch the relay and turn the oven on. It needs a 9v supply minimum. The biggest challenge however was with the doors. I routed a channel into the frame of the oven body, and used 3mm silicone automotive hose as a seal. This is 'glued' in place in the channel with silicone gutter sealant. This works really well, but as I discovered, the silicone tubing doesn't compress quite as well as I had hoped, meaning there is a lot of pressure at the hinge-end of the doors, and no pressure at all where the doors meet in the middle. Whilst the insulation structure on the doors made it a bit of an interference fit and helped, the pressure from the seal meant the doors would pop open about 30mm, which is obviously no good. It took me a lot of thinking and a bit of an experiment to come up with a solution for keeping the doors closed, starting with this not-so-aesthetically-pleasing sliding bolt method:  Not only did this look rubbish, but it didn't work 100% either as there is a bit of movement in the bolts themselves, meaning the door could still pop open about 5mm. This probably wasn't so critical, as it didn't leak a lot of heat out of that gap, but seeing as one of the main criteria for me was energy efficiency I wasn't happy about it. Eventually, I came up with the simplest and best solution:  This keeps the doors 100% closed against the seal, preventing any heat loss at all. It's perhaps not the most aesthetic option either, but again it was function over form for me. As for functionality, the oven works very well. It's incredibly efficient, with 0 heat transfer anywhere except the exposed aluminium frame at the front. I have run the oven up to it's cut-off temperature of 130 degrees, and the outside of the oven remains at room temperature - I could quite happily use it as a seat while it's at that temperature. The internal temperature is fairly constant, the edges run a touch hotter than the middle of the oven for the first hour or so of running time, but once it has had a chance to soak then everything stays within 1 degree. Total cost was about $450, $230 of which was for the PID controller and another $50 for the SSR.
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Hi thanks for this interesting thread.
I am wondering if an inexpensive bi-metallic or capillary thermostatic switch would not suffice, eliminating both the controller and relay? There would be fluctuations in temperature of <10°c but couldn't the cutoff temp be increased slightly or the time be extended to compensate for that? Do you use the Omega's PID control function?
If the fluctuations of a bi-metallic/capillary thermostat are too wide then a simple thermocouple, an Arduino and a few lines of code could be used to control the relay for consistent temperature control at a small fraction of the cost of a PID controller.
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