Comments: How to Build a Remote Kill Switch

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  • You might want to put a flyback diode on the main relay; when I built the circuit I had a lot of problems with the input pins on my microcontroller getting flipped by the switching noise from the relay. Moving the microcontroller further away from the relay also helps.

  • The rating on the main relay there seems a little low (28VDC for a 48V supply, and that's before talking about back-EMF from the motor...). You may want to try testing its ability to break the motor's operating current safely - a safety system that welds its contacts closed at the worst possible moment is no good to anyone.

    • It is indeed a 24V (contacts rated to 28V) relay but after significant testing it's done the job well. Worked great when our motor controller failed unsafe (100% throttle). That was exciting. Luckily, Alicia was watching and noticed something was wrong so hit the remote kill and I was able to brake to a stop.

      I had a hard time finding a solid, reasonably priced, readily available 48V relay. Please feel free to post other options/solutions.


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