acswitches
I'm replacing the motor control switch in this toaster and wanted to be certain about how it should be installed. It's a normal SPST neon rocker switch with A, B and C for terminals, and B-C being for the neon. It would simply be 1-A, 2-B, 3-C, correct?
Hopefully I wasn't too vague and I can provide more details if needed. Thank you for your help!
Yes it can be used to switch 220V. Viable? Well, cost and complexity could be issues for static switching applications. It's rarely done, which may be an indication.
Yes, you can detect and prevent destruction with a short (even if the short occurs at peak mains voltage) however you need a short-circuit-rated IGBT and you need to detect and turn off the IGBT quickly enough (and, strange as it may sound, not too quickly). Follow the recommendations of the manufacturer. These IGBTs are designed for use in VFD (Variable Frequency Drive) motor inverters.
I don't know offhand of other devices rated to survive a short-circuit on the mains- perhaps some beefy MOSFETs. Aside from that, an NPN transistor, an NPN darlington or a MOSFET could be used. In the latter case, in your first circuit, the body diode will share current with the external diode so you may see some additional heating in the MOSFET on top of (forward) conduction losses.
Edit:
Here is the spec from a typical short-circuit rated IGBT datasheet:
As you can see it can withstand a direct short-circuit for 10\$\mu\$s under realistic conditions (hot, with 300V across it).
For more on IGBT behavior under the stressful conditions of a direct short circuit, see this reference. Slowing the turn-off of the IGBT somewhat (especially during short-circuit conditions) can reduce the voltage spike due to inductance in the load circuit and the rapid change of current.
In my experience, it's usually not a good idea to directly mount parts that will be subject to repeated stress to a mounted PCB. After enough presses (hundreds?), the solder joints will crack, or pads can be lifted from the PCB itself.
You can avoid this by making a separate section of your pcb that will snap off for the button/switch to be soldered into. Then use flex or ribbon cable connector to connect it to your 'main' pcb.
For your LEDs, you can use dark translucent plastic windows so that the LEDs can only be seen when turned on.
Best Answer
To the schematic: JEEZ! Way to make a maintenance schematic that invites making stupid errors.
To your assumption/question/check: Yup. (after what felt like a year tracing hoppy black lines)
The top, 1, comes from mains White through the relay. The middle, 2, goes to the motors to turn them on. The bottom, 3, is connected to the mains Black. Since your motors are also directly connected to mains black, it's not a reversal switch. So you only need SPDT if you need to hard-brake them, which seems unlikely to me in the case of butter and bread transport (low inertia).
So the bottom pole is most likely for the Neon light, which turns on then A and B (1 and 2) are connected by the switch itself.