Ben's Home-Brew Solder Reflow Oven 2.0 Episode -- Episode 116

hi,

do you have the temperature profile graph for this code? how long is it supposed to wait at each stage?

That's kinda what I thought. I did find some further information after digging some more and it appears that the "ramp" phase is supposed to increase temperatures no faster that 2-4°C/sec, which this oven had no intention of doing even at 100% power (Ben's program was trying to do that at about 30% - probably right for the oven but a little more info in the video or in text would have been nice). I also found out that in spite of my oven implying with the dial it would reach 230°C, it never got above 147°C. That means it would ramp & soak but was never going to spike. Unfortunately that killed the project, but I was able to talk my employer into buying a real reflow oven after that (Prices have come down a LOT recently).

In case it helps anyone else, if it takes more than about 30-60 seconds to heat to the 140° point, you should change the profile of

75,140,45,125,205,20

to something more like:

255,140,45,255,205,20

and if your oven is really slow getting to the soak level, it may never reach the spike.

Thanks, Karen!

I consulted Ben and this is what he explained to me. You have to bring it up to temperature at a certain rate, then hold it at a certain temperature for a certain time, then spike the temp, then bring the temp back down.  The theory behind that is warming the parts up first then spiking the temp to flow the solder, but only for as long as needed, then allowing the whole thing to cool. Parts have a rating that will tell you how hot they can get before being damaged. Does that answer your question?

Yeah, I'm a couple years late on this, but I was wondering if anyone could explain the reasoning for the "ramp" value in the profile. I'm putting together one and it will not heat beyond around 112°C. My oven is a bit larger (needed to fit the boards I plan to do), which I suspect is part of the issue and was wondering how and why the ramp value was determined. I'm assuming that part of the reason is not to heat things too quickly, but how those numbers were decided upon, I haven't a clue.

It appears that when the variable 'state' is 1, it uses the PWM value for warming up, then transitions to state 2 where it just uses the relay pin as a digital to maintain the temperature for the soak period. States 3 & 4 do what 1 & 2 do but for the reflow. Problem is with the values in the profile, this oven is not going to heat up enough to get to state 2. let alone 3 & 4.

I know I'm probably going to end up solving this myself, but if anyone can give me any pointers so I'm not over cooking the boards.

Is there any kind of schematic and parts list for the build ???

If I could do it again (and some day I might) I'd go with an analog sensor for the thermocouples, as well as get thermocouples with less mass so they respond quicker.  Then I could do proper PID and control ramp rates.  Also I'd probably have a zero cross detector to control the relay better.

I know i'm coming in on this late, but after reading the data sheets, you get 5 reads a second on the 31855 as compared to 4/sec on the 6675.  The biggest improvement I see is that it is harder to lose track if you're in a race condition.

I'm just beginning my oven as in waiting for fundage, etc.  Mostly ready though.

Has anyone tried the Max6675 boards? Would they require mods to the source code to make them work in place of the Max31855 (I'd guess yes). The Max31855 boards are nearly x2 the price, and I'm working on a limited budget

You might want to look at this one, it looks pretty good.  I wanted to upgrade our oven with it but didn't get in on the kickstarter

https://www.kickstarter.com/projects/1070729460/zallus-oven-controller

Thanks to this video and a bunch of people I know that own DIY reflow ovens, I got my head around making my own!

I bought a cheap mini oven : 14L, 2 heating elements on top and 2 on bottom for a total of 1300W (announced).

I'm still waiting for the electronic parts to start the transformation from toaster to reflow.

I really want it to be able to display the comparison of the profile and the actual temperature curve on its screen. So I'll have to use a small dot matrix screen.

Obviously, it needs to be as accurate as possible for the temperature readings and the control of the heating elements.

"Beta" version will be using :

• an Arduino Uno R3
• only one MAX6675 board with a thermocouple type K
• a cheap lcd color display with SPI interface, probably the one with a SPI touch layer (if I get it to work)
• a 25A SSR "noname" (hopefully it won't catch fire )

If it works well enough, it'll bake its own upgrade, as I plan on making my own reflow controller board.

"Final" version :

• for the mcu, a STM8 or a STM32 (I would like to start learning to use those arm cortex mcu)
• two or three thermocouples interfaces, using either MAX6675 or 81855 (I got free samples from Maxim)
• eventually a small fan to cool the controller board (I'll have to see if the "knob section" gets really hot or not)
• maybe a large fan to improve the cooling speed
• and probably a SD card reader to easily add thermal profiles without having to reprogram the mcu

The color LCD screen that you can find everywhere (ebay, adafruit, ...) are mostly screens that were designed for old mobile phones. Most of the time, they're cheap and easy to use since there are many hobbyist made libraries for those screens.