There are several reasons for owning a home-made reflow oven these days.
1. Almost all worthwhile components are SMT now. Hard to hand-solder as I get older.
2. Circuit boards and stencils are dirt-cheap nowadays.
3. I find myself wanting to make my devices smaller and smaller so I must use SMT devices.
4. A reflow oven would be something cool to build.
I am fully aware that there are ready-made kits for something like this. I just want to try it myself. Maybe I learn something in the process.
So, as per my last log, the oven is not heating up fast enough partially due to thermal losses. I decided to do the best I can insulating it.
I insulated the inside using a self-adhesive mat that we use at work for engine heat rejection from the exhaust manifold. It is apparently rated for 300C so it should do. We'll see how it holds up. The back of this oven is a single piece of sheet metal so that's probably the worst area for heat loss. There is a piece of insulation on the bottom of the oven as well. I screwed the top pieces into the sheet metal. Even though the insulation may hold up, the glue might not and then it will fall on top of the heater. That clearly can't lead to anything good.
Then I took the cover off and used tin furnace tape to seal all seams between the "heat box" and the body of the oven. This was a rather tedious process but I can only hope that it will improve things as a whole.
Finally, before putting the cover back on, I noticed that there is a fair amount of air gap between the heating box and the cover. I suppose this was just more room where insulation could be added. Had to stick the insulation to the cover so that the shiny side was pointing towards the "heat box". No screwing down was necessary since once it is pressed together (the insulation was a bit thicker than the air gap) it will have nowhere to go.
Once it was bolted back together, it looked pretty good. I didn't like the fact that I can't see inside it now since I added insulation to the glass door. I supposes one can't help this.
So I roughly threw some stuff together and came to an unpleasant realization: the oven is VERY SLOW to heat up, even at full output on the heaters. Once it gets going thought it climbs fairly well but it becomes very hard to stop. One note that a colleague made is that the back and sides become extremely hot to the touch. This got me thinking that all my heat is escaping through the sheet metal and around the front door. I surmised that dealing with these losses should be my first course of action.
I'm going to need to control temperature and heating time a bit better than when I'm cooking a pizza pocket. So I took a look at a classic profile from ChipQuick. This is how it has to look like in the end.
My idea is to print a small box containing the electronics that can sit next to the oven, just like a 3D Printer setup. When not in use, the wires between the control box and the oven get disconnected and the box can be hopefully stored INSIDE the oven.
In order to start making this, I started rummaging through my basement.
Here's what I found (that was relevant to this project):
One Kenmore 110V 1000W toaster oven -> This oven is less than ideal for this because it has resistive elements. On the upside, it's basically free since I didn't use it in over a decade.
Arduino 2560 -> Good for this project - lots of memory.
TinyRTC sporting a DS1307 w/ AT24C32 EEPROM.
4x20 LCD display.
I2C to LCD piggyback adapter -> This is a really useful piece of equipment.
MAX6675 w/ thermocouple -> Cables are steel-braided and good to 600C.
SD Card Reader -> Full size SD - quite an old one.
Grayhill 62P series quadrature encoder. This is great for an input - just like a 3D printer. Unfortunately it does not have a feature for pressing a push-button so I will have to implement that separately.
One button for OK.
One piezo-beeper for user notifications.
I took apart an old power adapter to use as the power supply for the Arduino. 110VAC to 12VDC.
Several MOC3043s and some MAC12DG triacs. I have a serious disdain for relays so I'm avoiding them as usual.
A square 80mmx25mm 12V fan for cooling the heatsink for the triacs.
A quick brainstorming session yielded the below preliminary schematic.