How to make a homemade coil tester

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In this article mechanical girl explains how to make a simple coil tester based on a relay oscillator. Very simple to do at home.

How to make a homemade coil tester with reley


Following the wave of testers for equipment in our car, here I bring you a proven invention of how to make our coil generate the sparks. Without further ado, I show you below:

 diagrama probador de bobinas

It is based on the popular relay oscillator, modified a bit by adding a capacitor and a rectifier diode. The materials are the following:


Power supply of 12V and 10A at least.

RL1 - NO and NC double contact relay of Bosh type or for printed circuit.

D1 - Rectifying diode 1N4007

C1 - Polyester capacitor 0.33 uF

C2 - 22uF electrolytic capacitor

Push button normally open.

And of course a coil dry, or in oil.


Consideraciones importantes:

Do not use electrolytic or tantalum capacitors for the C1 (which goes on the coil) because this type of capacitors are polarized and do not support the high frequency variations of the coil (Do not use it because they heat up and explode hahaha).

Use it with 12V and 10 A power supplies at least. The coil consumes a lot of power. If you use less current, the coil will not have enough power to spark or make one or two sparks and the supply voltage will drop.

Do not mount it in the car, or directly to a battery that is connected to the vehicle. Remember that we are generating high voltage, this passes through the insulation of automotive cables (these insulators only support 1,000 V and the coil produces 30,000 V) very easily, and if a spark jumps to one of them DAMAGE THE CAR COMPUTER u some other electronic element. So VERY CAREFUL WITH THAT.

USE A SPARK PLUG CABLE for the high voltage output of the coil. In my video I use a normal cable for the high voltage terminal of the coil, but it is because I am doing experiments and I know that the spark will not jump through the insulation because I separated it enough from the ground wires.

Be very careful with HIGH TENSION, if you use a pacemaker or any other electrical device that supports you, please do not do this experiment.

Here I show you a video how the tester is made.

 Well, that's all for the moment, I hope you like it.

Do you have questions or doubts?

Questions or suggestions can use the form below and I will gladly answer them.


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Written by Dennis García.

Mechanical Girl


Muy buen trabajo

Gracias Dennis por este otro probador.

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    How to make a homemade coil tester

    How to make a homemade coil tester

    In this article mechanical girl explains how to make a simple coil tester based on a relay oscillator. Very simple to do at home.

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    4 Question(s) answered

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    • Asked by Edgardo
      on 04/01/2020
      No entiendo como cierra el circuito Answer:
      Mmmmm, ¿donde no cierra el circuito Edgardo?
    • Asked by Edgardo
      on 04/07/2020
      Analice el circuito y si esta cerrado pero cuanto es el pulso de duración, deseo hacer uno con pic, y saber como haces con los capacitadores para saber el tiempo. Vi el video y tienes en la regla de prueba un filtro electrolítico. Gracias Answer:
      Escribeme por email la duda que tienes a y yo te respondo por allí con más calma.
    • Asked by Ángel Manuel
      on 04/09/2020
      Buenas una pregunta este circuito se puede usar para encender un vehículo con distribuidor a platino en caso que se halla dañado el condensador y nos quedemos varados Answer:
      Si, es posible sustituir el condensador por este que indico. Tendrá menos potencia, pero podrás arrancar el motor y salir del apuro.
    • Asked by Joycee
      on 11/22/2020
      Buen dia saludos desde mexico. Solo quiero saver de que valor y wataje es la resistencia que uso Answer:
      ¿Cual resistencia? ¿Te refieres a la de la bobina? esa la trae ella, es de 10 ohms y los vatios...caramba, esa es como de 50W o más.

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