DIY Induction Coil Design

Written by brendan conuel
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DIY Induction Coil Design
Induction coils were a critical component in the first generation of x-ray machines. (x-ray image by Claudio Calcagno from

An induction coil is a device consisting of two separate, unconnected coils of wire wrapped around a single metallic core. When current is run through the inner coil, a magnetic field is created. Then, when current is rapidly shut off, the collapse of the magnetic field induces a voltage in the second wire that is proportional to the ratio of how tightly wrapped the two coils are respectively. If the difference in coil wrapping is substantial, this voltage can be enough to create a spark that will jump across a small gap.

Skill level:

Things you need

  • Iron rod
  • 2 long spools of insulated copper wiring
  • Battery
  • Wire stripper
  • Light switch

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  1. 1

    Connect one end of your first spool of insulated copper wire to one terminal on your battery.

  2. 2

    Wrap the remainder of the first spool of wiring around the iron rod. This coil should be wrapped moderately tightly - a couple hundred turns in total should be ideal.

  3. 3

    Run the free end of the first coil of wire through your light switch set to "off" and then connect it to the open terminal on your battery.

  4. 4

    Wrap the second spool of insulated wire around the iron core as well, on top of the first spool. This coil should be wrapped very tightly - a couple thousand turns in total should be ideal.

  5. 5

    Strip half an inch worth of insulation off both ends of the second coil of copper wire using your wire stripper.

  6. 6

    Position the two stripped ends of the second spool of copper wire next to one another and separated by about half a centimetre or so.

  7. 7

    Flick the light switch on and off rapidly. This rapid variation in current through the first coil of wire, and by extension its magnetic field will produce a voltage that ideally will be sizeable enough to cause a spark to jump the gap between the two stripped ends of the second coil.

Tips and warnings

  • Different applications and different wire winding configurations will lend themselves to different battery voltages. Experiment with a variety of different batteries, and judge for yourself which yields the best results.
  • If switching the power on and off manually proves to be too much of a hassle, consider buying or building a device called an "interrupter," which will rapidly switch the current for you.
  • Be careful not to situate your spark gap near anything flammable or where it may come into contact with human skin. A well-built induction coil can produce quite high voltages capable of being painful or dangerous.

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