By Jason Thompson • Updated Mar 24, 2022
An electromagnet is a versatile device that emulates a permanent magnet’s behavior and offers the ability to adjust its magnetic field on demand. By winding conductive wire around a ferromagnetic core and supplying it with electric current, you can create a magnet that is as strong—or as weak—as you require. While building one at home is straightforward, overheating can become a serious issue if the wire is subjected to voltage or current beyond its capacity. With a thoughtful design process, you can avoid this problem and ensure a reliable, safe electromagnet.
Determine the coil’s diameter (the distance from one side of the coil to the opposite side) and multiply it by π (3.14). Then multiply that result by the number of turns in the coil. The product gives you the total length of wire needed for the electromagnet. Use the same units (inches or centimeters) that you measured the diameter in.
Refer to a wire gauge resistance chart and pick a gauge. Look up the resistance per unit length (ohms per foot or meter). Multiply that value by the wire length calculated in Step 1 to find the total resistance of the chosen wire.
Divide the battery voltage by the total resistance from Step 2. The quotient gives the current that will flow through the coil once it’s powered.
Compare the calculated current to the maximum current rating for the selected gauge on a current‑rating chart. If the expected current exceeds the gauge’s limit, choose a lower‑gauge (thicker) wire and repeat the calculations. Continue this process until you find a wire that can safely handle the current without overheating.
More coil turns and higher battery voltage increase magnetic strength, but you must also select a wire gauge that can carry the resulting current safely to prevent overheating.
