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I'm hoping someone could help me out with this one final issue with my project.

I have an ESP32 that controls a magnetic starter. The issue is when the magnetic starter hits the off switch, the esp32 restarts. This happens even if I hit the external off switch (not via the ESP32 gpio to relays).

The wires from the magnetic starter come onto the PCB, pass through the relays, and then exit without actually going into any of the circuitry.

This even happens when the ESP is powered by a separate power source rather than through the power coming from the magnetic starter.

Any advice on what I could do to solve this would be greatly appreciated.

Relays I'm using

Schematic PCB MagneticStarter

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  • \$\begingroup\$ I’d suggest you refrain from using that pcb design as there is insufficient clearance between the mains tracks and the extra low voltage circuitry. There is a real possibility of electrocution. As well, the layout is not very good. I’d suggest adding a varistor across the contactor coil and maybe three across the motor phases. \$\endgroup\$ Commented Jul 2 at 14:22
  • \$\begingroup\$ Based on your feedback, I completely separated the relays and power source from the PCB. I'm still having an issue though. When the motor starter starts, everything is fine. When the off button is hit, it causes some issue with the arduino and causes it to reboot. The wires from the motor starter don't come in contact with anything on the pcb. They go into the relays and out, never touching the PCB. I checked the voltage going through the wires, and it's only 8 VDC, so the relays should be able to handle it just fine. \$\endgroup\$ Commented Jul 9 at 0:10
  • \$\begingroup\$ I see no Arduino board, do you mean the ESP32? Try running the ESP32 from batteries in order to determine if the interference is coming from the mains supply through the psu module. You could also try putting a 14mm varistor of the appropriate voltage across the contactor coil. \$\endgroup\$ Commented Jul 9 at 13:19
  • \$\begingroup\$ Yes, I'm using and esp32 running arduino. I tried powering the esp32 through my laptop rather than the mains, but it still restarted. I have a schotty diode across the contractor coil. Is a varistor better? \$\endgroup\$ Commented Jul 9 at 14:25
  • \$\begingroup\$ What voltage is the contactor coil? A Schottky diode is probably not the preferred choice. You might need to add varistors across the motor. \$\endgroup\$ Commented Jul 9 at 15:55

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So I kind of solved it. I was going to try to use completely different relays as I read someone else having a similar issue and they just used different relays. But then I saw that I had a relay module lying around that is opto-isolated from the signal currents, and figured, let's try that.

From closely looking at the module, it seems like it's fairly similar to what I was doing before. It has a mosfet or npn transistor to power on the coils and it has a diode (not a varistor) across the coils. The relays are 5v rather than 3v that I was using, but I don't think that made a difference (I was driving the old relays with 3v, and this new one with 5).

The only difference I see is the different relays and the optoisolator. So that seems to solve it. It still doesn't quite make sense to me that when remotely turning off the motors (not using my circuits), that surge goes through the relay, but not the coils, but still causes issues with the esp32.

enter image description here

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  • \$\begingroup\$ The optos on those boards tend to do very little. It could be more due to wiring layout than the relays themselves. The core issue is most likely the inductive spike generated when the contactor opens - thus my suggestion of adding a varistor across the coil to manage this. Putting varistors across the pushbutton switches might achieve a similar result - depends on the ‘magnetic’ starter whatever that entails. Sounds like the classic DOL starter to me. \$\endgroup\$ Commented Jul 10 at 5:01

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