DIY: How to Make Your Own 12Vdc Electromagnets

Written by doug leenhouts
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DIY: How to Make Your Own 12Vdc Electromagnets
Current running through a coil creates an electromagnetic field. (coil image by Alison Bowden from

Electromagnets can be created using a conductive wire and a 12-volt battery. They can be used to magnetise tools or other metallic devices that are not naturally magnetised. These magnets are often preferred to permanent magnets because you can simply disconnect the battery and the magnetic field is removed. The strength of the electromagnetic field can be controlled by adjusting the number of coils in the wire; adding coils increases the field strength and, conversely, unwinding a few coils decreases the field strength.

Skill level:

Things you need

  • 1-inch-diameter iron bar
  • 14-gauge insulated copper wire
  • 12-volt battery
  • Wire stripper
  • Wire cutter
  • Screwdriver
  • Electrical tape
  • 1-inch metal screws
  • Knife switch

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  1. 1

    Wrap the insulated wire around the iron bar in a coil. Keep the windings as close together as possible. The iron bar will become magnetised and add to the strength of the electromagnetic field. The more windings the coil has, the stronger the resulting electromagnetic field will be. The equation for determining the magnetic field strength of the solenoid is B = (u)(n)(I), where "B" is the magnetic strength, "u" is the permeability of the iron bar, "n" is the number of windings divided by the length of the coil, and "I" is the current flowing through the coil.

  2. 2

    Strip the ends of the wire about an inch from the ends with the wire stripper. Twist the copper strands for a better connection to the battery terminals. Cut a short section of wire with the wire cutter, and strip both ends.

  3. 3

    Connect one end of the coil to one of the terminals of a simple knife switch. Connect the second terminal of the switch to the positive terminal of the battery with the short wire you previously cut. Bend the exposed wire ends in a hook and wrap them facing clockwise around the terminal screws, and secure them with a screwdriver.

  4. 4

    Wrap the other end of the coil wire around the negative battery terminal. Secure it in place with electrical tape.

  5. 5

    Move a screwdriver close and parallel to the coil for a few seconds. Then move the screwdriver near some small screws to verify that the electromagnet magnetised the screwdriver.

Tips and warnings

  • You can disassemble a car alternator to find sufficient lengths of insulated wire.
  • A magnetised screwdriver is handy for holding onto screw heads when working in hard-to-reach spaces.

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