The Oven

[bpiphany]

Don't you hate being plain old average?

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Then do something about it. Sum up some stuff.

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And be awesome!!

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oven2.JPG (226.16 KiB) Viewed 1925 times

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oven4.JPG (227.9 KiB) Viewed 1925 times

[bpiphany]

The story

Thinking it was about time to move on from my toaster re-flow oven, I bought a mini oven (aka toaster oven) from one of the big Swedish hardware chains. It came with one baking plate and one grate (and a nifty tool to grab them when hot). I figured the plate would be good for spreading the heat more evenly. So I thought about buying another one just for the plate, and the extra power would come in handy as well. Sadly the combined amperage of two ovens would be slightly more than a 10A fuse can handle. So I decided I better get two extra and wire them up to a more powerful power source =D

The ovens come with four heating elements, two in the bottom and to in the top. They are 1380W combined (I presume that is at 240V and 5.75A). There is no insulation around the inner compartment, and the bottom and back of the oven is only a single plate.

I took the oven apart completely and drilled extra holes for the heating elements, they are now six each in the bottom and top. They are wired in their original configuration of two groups of two elements in series. Each group is connected to it's own phase. The total 4kW should be relatively easy to handle for the 3x16A three phase outlet.

The power inlet is a regular cable plug which I cut down a bit. It has a sort of bayonet assembly which let me jack it into a properly sized hole. I had to put it in the lathe to make some extra room for the plate, but after that it fit perfectly.

Since the back plate will become hot from being in direct connection with the oven compartment and I am planning to mount the relay onto it (along with the controller and other stuff) I extended the case backwards a few inches. Glass fiber insulation will be added when finishing up the last bits and pieces.

I don't quite know what to use the knobs for. The power indicator light will of course be used just for that. I hope the Oven will be overkill enough to require some sort of LCD display for temperature and power display.

[seebart]

can´t wait to see "The Oven" in it´s modded state!

[bpiphany]

I'm waiting for the relay, and some glass fiber insulated wires to finish it up. Other than that it's more or less finished. I haven't added insulation yet, don't want to mess around with that until I screw it together the final time..

The most interesting parameter to find out about is what temperature change rate will be possible to achieve, and if I will be able to control the temperature curve in a good way. I've started messing around a bit with temperature data logging and PID controllers.

[bpiphany]

From PCB to char in 120 seconds...

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With a similar setup as in http://deskthority.net/workshop-f7/toas ... ml#p210768 I made a test run of the oven before adding the relay or any insulation. I pulled the power when I the thermocouple reached 250°C. I should have realized it would overshoot by quite a bit. I was in a rather well ventilated room separate from the rest of the building, but the smell spread everywhere, even to nearby buildings =P

Since then I received the relay. Unfortunately it didn't work. Amazingly it popped open easily and with some luck I was able to repair it. One of the terminals for the control voltage had no connection to the internal circuitry, and even though the whole thing is filled up with epoxy I was able to patch it with a jumper. Unfortunately it (probably not even if ever functional) doesn't meet the 3-32V specification, so I had to figure out a way to supply 12V from a separate power supply controlled by a 5V Teensy..

Now I just need to trim in a PID controller to have a useful oven. And take more photos...