Introduction: DIY Anti-Spark Switch

About: After a degree in micro-engineering in Switzerland, I moved to Russia to discover new landscapes

I made an electric bike and each time I connect the battery, I feel like the guy in the movie who is stealing a car and trying to start the engine by touching the wire he just ripped: I have spark between my fingers. I imagine that the same happens inside the switch when I turn it on. I decided to react.

It should have a capacitor at the input of my electronic speed controller (ESC) and I guess that it is responsible for drawing such current when I plug the battery. So the idea was to limit this current briefly and then return to a simple connection with no resistance. This is the purpose of this system.

Step 1: Get the Components and Solder Them


  • soldering iron
  • third hand or vise
  • multimeter (not required)


  • relay ( 24V, 240VAC 10A in my case)
  • switch
  • connectors
  • 10ohm resistor
  • heat-shrinkable sheath
  • nail polish (not required)

The key part of this system is the relay. Find one who works at the battery voltage (24V in my case). When I turn the switch on, the ESC capacitor is charged through the 10 ohms resistor. The relay remains open until the ESC capacitor voltage reach 18V. Then the relay closes and bypass the 10 ohms resistor.

I used the heat-shrinkable sheath for insulation and some nail polish for the small part. Any conducting part has to be covered.

Once the components soldered according to the schema, test with a multimeter that there is no short circuit. Double check that the minus connector goes to the minus battery pole and to the minus pole of the ESC. I know that the circuit is not complicated but any mistake will probably lead to a smoked drama. This is why I insist so much on the verification.