Reflow Oven Build – Part 1

There are many tutorials, instructables and youtube videos about DIY reflow ovens. I have checked out some of them myself before deciding to make my own. This however is not a tutorial or a set of instructions on how to build a reflow oven. This is a just a record of the steps I took to build my reflow oven in case some of my (crude but cheap) methods suits you.

Parts used:

  1. Rival 4 slice toaster oven – I got this from Walmart for $23 (CAD). The main reason for choosing this other than it being cheap is that it has quarts type heating elements, which warm up fast and cool down fast unlike the thin grey type heating element found in most regular ovens
  2. Arduino Micro – I already had one of these lying around that wasn’t being used for anything else.
  3. K-type Thermocouple – $4.50
  4. MAX31855 thermocouple amplifier breakout board from Adafruit – $14.95. This was a rather expensive choice. But this breakout board accepts 5V inputs and outputs the temperature in digital, making the coding and the rest of the circuit fairly simple.
  5. Solid state relay (SSR) – $19.95. input: 3-32 VDC, output: 24-380 VAC, 25A
  6. Heat sink for SSR – scavenged from an old project
  7. Computer fan – rescued from an old PC power supply unit
  8. 12V DC power supply – Burrowed from my Music and Lights project

Total spent for parts above: $62.40 (CAD)

I broke the design of this reflow oven into three Major parts:

  • oven
  • controller
  • user interface

The oven

The oven must be capable of heating up and cooling down at a rate sufficient to follow a reflow temperature profile. A slow oven that stays too long in the critical zone of the reflow profile (above 217 °C) could potentially end up damaging the components.

Most of the home made reflow ovens I have seen started out as typical toaster ovens. But typically a toaster oven manual does not say how fast it can heat up or cool down. So which one to choose? Some sources suggest to use a toaster oven that has quartz heating elements. Since this type of toaster oven was proven to work in the R&TPreppers video, I decided to get the cheapest toaster oven I could find nearby that had quartz heating elements.

The quartz heating elements of the toaster oven
The quartz heating elements of the toaster oven

Step 1: Open the case and strip all the knobs and dials (2 in this one) that are no longer necessary. That job will be taken over by the reflow oven controller.

Remove the existing controls of the toaster oven as they are no longer needed
Remove the existing controls of the toaster oven as they are no longer needed

Step 2: Cut a hole on the side of the oven to attach the cooling fan. This fan keeps the electronics (most importantly the solid state relay) inside the reflow oven cool. It needs access to fresh air, so I had to cut a 6 cm diameter hole on the side of the cover. The metal case was thin so I was able to cut it with a heavy duty scissor (not a very clean job, but got the job done).

Attach the PC fan to the side of the cover to bring cool air inside to keep the electronics cool

Step 3: Attach the SSR to a heat sink and mount the heat sink on the other side of the hole so that it is in the direct path of the cold air coming from the fan.

SSR attached to a heat sink and mounted directly opposite the cooling fan inside the oven cover

Step 4: Drill a small hole into the oven chamber to feed one side of the thermocouple wire.

A small hole drilled to the side of the oven chamber brings in the thermocouple

Step 5: Wire everything up that goes inside the cover of the oven. This includes all the connections shown in the wiring diagram below

Wiring diagram for the components inside the reflow oven.

Once all the wiring is done and the cover is put back on the reflow oven is built! But without a controller, this oven is pretty useless. So in the next post I will cover the controller. Most reflow ovens I have seen integrate the controller inside the oven as well. But since I have no idea how hot it will get inside the cover when the oven is running, I thought it is better to have the controller outside. Also having the controller outside makes it easier to program it.

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