Works - Oven Selection is Critical
by Constantin von Wentzel on July 21, 2012
I bought this shield a while back to enable my $30 toaster oven to do reflow under more controlled conditions. The board arrived, it works, though the 1.1 firmware did not support the fan output (even though the hardware does).
I added software support for the fan, also put in an alert if the oven temperature is too high to start the next reflow session - now an error message appears instead of the unit aborting silently. The other button now allows the unit to switch from leaded solder temperature profiles to lead-less ones and back. See my fork on github (CvW) titled version 1.2
A couple of observations: I used a Crydom D2425D Dual 25A SSR. They work great but they also require a heat sink if you want to use them all day. I gutted the oven instead of using an external approach per rocketscream, which makes for a slightly cleaner installation. However, I overlooked a diode on the return wiring, which disabled the SSR/Triac. Once the Diode was gone, the rig worked great.
Another observation re: toaster ovens. Try to find one with a very high output but a tiny interior volume. Otherwise, achieving the desired 3*C rise rate is difficult, if not impossible, especially on 115V circuits like in the USA. I ended up insulating my oven inside and out to reduce heat loss. Insulated areas include the walls inside the oven cavity, the dead space between the cavity wall and the exterior of the unit, etc. Eventually, I will also get much of the glass door covered. Reducing the thermal mass not only reduces cycle time, it also decreases your electricity bill.
by Constantin von Wentzel on July 19, 2012
I bought a standard toaster oven with a convection feature and opened it up. Once inside, I was able to remove all the controls and preserved the wiring for later reuse. I bought a Crydom D2425D SSR on e-bay to run the heaters and the fan. The heaters consist of four quartz elements, which are arranged in series-parallel. I added a terminal block to allow the use of ring terminals on the Neutral side.
I mounted the Arduino in a box on the outside of my oven. Feeding the cables through existing holes was painless, I bought some pre-crimped wire assemblies from Pololu, which made making a custom pin header for the Crydom SSR really easy.
One thing to consider is heat, i.e. the SSR will heat up while it operates. I made it into reflow before the unit got warm. I subsequently bought a heat exchanger for the SSR - It has the added benefit of encapsulating the screws I used to mount the SSR inside the oven.
I also added a lot of 2000*F rated insulation to the oven to allow it to heat faster and to reduce the exterior temperatures. I placed insulation in the dead space between the inner oven surface and the outer oven surface as well as on the bottom between the quartz elements and in front of the back wall (which had no dead space!) I may add more insulation on the inside to cover the inner side walls, the area between the top quartz lamps, and much of the window. However, I believe I'll need to use rigid insulation for that task, something I'll have to order.
Unfortunately, I didn't realize that I had the orientation of the Arduino wrong - the LCD is thus upside down. If I find myself with too much time on my hands, I'll investigate if the font can be turned upside down or if I will have to come up with a custom font.
Additionally, I am surprised that rocketscream elected not to document the fan pin explicitly, either in the Arduino code or the Wiki. I'll have to look at the schematics to figure that one out. As you may guess, the fan has yet to get a role also. I'd like to see the fan running during heat up, soak, and reflow, perhaps turning off during the cooldown phase?
Last but not least, could the rocketscream team also include a leaded reflow profile for the oven? I think it would be great if the user could switch between profiles using SW2. Just a suggestion. Anyhow, this is a great product, I wish I had installed it sooner.
by Kerry Veenstra on June 17, 2012
My Reflow Oven Controller Shield is working well and has reflowed several boards using leaded solder paste.
The oven modification was simple: I inserted a solid-state relay in series with the oven's existing thermostat using two pieces of high-temperature appliance wire. Setting the oven to bake at its highest temperature turns on the convection fan and energizes the thermostat in preparation for reflow soldering a board.
I ended up using a simplified version of the provided control software. The simplified software does not use the PID library. Instead it just turns on the oven 100% except between two temperature points where it cycles the oven at 50%. At a final, highest, temperature point the controller turns the oven off and beeps to alert me to open the door for cooling. This form of open-loop control has been adequate with the toaster oven that I have.
Remember to use a K-type thermocouple or else the temperature measurements will be inaccurate. I needed to remove a stainless-steel sheath from the thermocouple, exposing it directly to the air, to improve its response to temperature changes.
When this kit will be for sale
by Jesus Carrillo on February 24, 2012
Hey, I would like to have a kit like this, I'm not from the US but I will be going in the next weeks and I would like to buy one of this and get shipped to my Hotel is posible to have one of this??
Thanks! jesuscarrillo8 AT gmail