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Need help figuring out AC wiring scheme in toaster oven

Discussion in 'General Electronics Discussion' started by Solidus, Sep 7, 2014.

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  1. Solidus


    Jun 19, 2011
    Alright folks,

    Recently I've decided to start doing some BGA rework in my spare time to make me a few dollars of side money for my other projects. As you are probably aware, doing this with any degree of sophistication requires a reflow oven, so I decided to use an Arduino, SSR, and thermocouple to provide for the reflow ramp and profiles and what not.

    The body of code, hardware setup and everything I've got very well figured out, but the issue is the AC wiring scheme in this toaster that I'm using. Being a college student, I happened to take over one of my dad's old microwave-convection oven combo units (nothing beats free!), and first order of business was to strip out the magnetron as well as associated circuitry.

    The wiring for the heater coils though for the convection that I'd ideally be putting through the SSR is more complex than I expected. It appears that there is a single coil, fed by a blue wire and a white wire. I'm assuming that this set of lines would be switched 115VAC. However, the blue wire tees off where it inserts into the heater coil into a fan, which makes me tend to think that the white wire corresponds to the 'hot' AC line, the blue being the neutral, and the heater coil being fed by a switched, lower-voltage AC source, most likely from the supply transformer, that is connected as inverse phase.

    I've drawn out the setup on a piece of graph paper. From clockwise, left is the heating arrangement as is in the oven currently, top right is what I presume the voltage sources would look like in terms of phase and what-not, and bottom is the block diagram of how all the systems are derived in the oven, from following the main line in to the outputs (magnetron/convection heaters).


    I decided to post this to see about getting your opinions because I would rather not take the first option that came to my mind, and that is probing the heater terminals while the oven is live checking for 115VAC. Is this a setup that makes sense? If so, I can simply pull the terminals to the heaters and rewire through the SSR, just having to generate a lesser voltage as well for the fan. If it isn't, I'll have to figure out some other options.
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    I think we need to see what's to the left of the three wires that enter at the top left corner. Without knowing that, I would assume that the blue wire is neutral, the orange wire is switched phase for the fan, and the white wire is switched phase for the element.
  3. Solidus


    Jun 19, 2011
    Okay. I'll try later today to get some photos and what not of the wiring bundle that it is a part of.

    I originally tried to make a judgment based on that section of wiring only without needing to disassemble the part of the housing containing the logic boards and controller elements. But, as I'll work on it later as well as mock up a better-looking schematic.
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