How to Wind a Toroid

Cut a 6-inch piece of magnet wire using the cutting edge of the electrical pliers. Insert one end of this wire into the center of the core and tightly loop the wire around the core once. Mark where the loop begins and ends using the permanent marker.

Unwrap the wire from the transformer core and straighten the wire until it lies flat. Measure the distance between the marks and write this measurement down; this measurement represents the amount of wire it takes to make one turn around the transformer core.

Multiply the number of windings you wish to wrap around the core by the measurement obtained in the previous step, and add 4 inches to that measurement to obtain the wire length needed to wind the toroid. For example, if one turn takes up 1 inch of wire and you wish to wrap the wire 30 times around the core, multiply 1 inch by 30 turns to get 30 inches. Add 4 inches to this measurement to obtain 34 inches, which is the length of wire needed.

Hold the toroid in one hand using your thumb and index finger so half the toroid hole is exposed. Insert half the wire length through the toroid hole using your other hand, and tightly loop the wire around the core. Do not allow the wire to scrape on the inside corners.

Repeat the previous step with the second and subsequent loops around the core until the wire has been wrapped around the core. Leave 2 inches of slack at each end of the wire. After all the turns are on the toroid, spread the turns evenly with the tips of your fingers until the wire turns cover about 90 percent of the core.

Use the sandpaper or emery board to gently file off 1/2 inch of insulation from each end of the wire.