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I'm converting a 1500W toaster to a reflow oven with PID control, but I'd like to focus on the hardware aspect.

I've pulled the switches and controls out of the oven and I'm left with something like this as if the oven is in bake mode which is all heaters and the convection fan:

schematic

simulate this circuit – Schematic created using CircuitLab

At the bottom is the "new circuit". Is this a "good circuit" for the controlling the top and bottom heating elements? Anything to look out for? I'm open to suggestions for improvement of the design as well.

I'd like to keep the convection fan intact as to keep the top and bottom more evenly heated.(It's a shaded pole motor like this)

I'll be using all of the correctly rated hardware electrically and thermally speaking. Heatsinks and cooling fan will be used on the SSRs.

Update: The second, modified, circuit with the SSRs works.

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  • \$\begingroup\$ Your first schematic diagram is not complete and we can't see what you are working on. I don't think that anyone here can tell you where the diode goes - you have to trace it out and update your schematic with that information. We don't like doing GIGO here (Garbage In, Garbage Out). \$\endgroup\$ – Dwayne Reid Sep 1 '15 at 22:58
  • \$\begingroup\$ @DwayneReid The Diode is only used for the "keep warm" mode and does not seem to be connected when in bake mode. See the updated circuit. \$\endgroup\$ – GisMofx Sep 2 '15 at 1:29
  • \$\begingroup\$ Did you calculate the heat dissipation in the SSR yet? Might want to check that before you get too much farther. Most of the ones I have seen have fairly high resistance compared to relays. \$\endgroup\$ – mkeith Sep 2 '15 at 3:45
  • \$\begingroup\$ @mkeith I'm using 25amp SSRs and the total power consumption is 1500watts. Roughtly 6.25amps through each the top heater and bottom heater individually(less whatever the motor draws). A healthy safety factor. The SSRs have heatsinks and don't get warm. I plan on adding a case fan as well. \$\endgroup\$ – GisMofx Sep 12 '15 at 21:22
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Your new circuit (2nd diagram) should work just fine.

You need to calculate how much power the SSRs will be dissipating. Assume that there is a 1 Vac drop across each SSR. Because you didn't mention in your question how much current the oven is supposed to draw, we can't estimate how much heat you need to get rid of.

You may also want to put a SSR or relay on the convection fan.

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  • \$\begingroup\$ It's a 1500watt unit. I've got 25amp zero-cross SSRs. I'm not sure of the motor wattage, but I'll assume 750 watts for each top and bottom, to 6.25amps. In the original diagram, do you know why in the the hot line was connected to both ends of the heater "array"?..Something I don't fully understand with AC circuits. \$\endgroup\$ – GisMofx Sep 2 '15 at 12:14

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