From the show notes of Amp Hour #221, Chris mentions he is starting a reflow oven project.
some notes for Chris and all on what I made a year back or more. Uses electric imp to make a head-less design and gui interface super easy.
- Convection: I assume it helps. I never tried it an other way and others have stated it is necessary for even heat
- Feedback: I place all boards on a copper sheet that I blackened. One spare board has a thermocouple soldered to it.
- Power: I boosted mine by shortening the heater wires. It's a bit of labor but it worked well. Mine went from 1200W to 1700W
- GUI. I use a web page and so I did not have to design and build any buttons on the hardware. What a relief.
- Safety: Wire the mechanical timer in series with everything. Regardless of any software, this mechanical timer will shut it down after n minutes.
- Control: I control slope of the temperature in the PID loop directly instead of Temperature. I think this results in much more stable control.
- state 1 preheating at super low duty cycle until you reach 40C (perform error checking at the end of this)
- state 2 Drive upward at 1.5C/second
- state 3 At ~100C change your target slope to one that will get you to 150C after 70 seconds (example)
- Continue re-computing the target slope in the loop and you will smoothly turn the corner into the soak
- state 4 After appropriate time expires for the soak, drive upward at 1.5C per second to flow.
- remove from oven at temp you like: for example 215C
By constantly computing the slope and using that as the loop instead of temperature, the web page can extrapolate and continue to update the screen at a higher refresh rate than the data that comes in. This gives you precise real-time display of the temperature with no lag by virtue of how much inertia the oven has.
I shared everything I could about my project but...
of course I realize everyone makes their own oven, no two are alike and that is the fun of it!One possible oven:
on Amazon, this Black & Decker model - TRO4075B - is only $54 and is 1500Watts. about as high as it goes these days.
I made mine from a similar $40 model that seems to be discontinued now.
Soldering thermocouple to the sense pcb with extra high-temp solder
http://mjkuwp94.tumblr.com/SolderingTarnishing the copper
http://mjkuwp94.tumblr.com/tarnishingPID Constants
http://mjkuwp94.tumblr.com/PIDSlopeMain page containing documentation of the whole project
http://themzlab.tumblr.com/reflowoven